Lecture 11 - Vaccines
mRNA technology
1) 1960s = mRNA discovery 2) 2005 = nucleoside modification reduced immunogenicity of mRNA 3) mRNA vaccine technology had been in development for a long time before COVID-19 surfaced
What are examples of adjuvants?
o Saponins (give immunostimulation) o Netural liposomes and microspheres (depot/carrier) o Mineral salts and aluminium (immunostimulation and carrier o Cationic liposomes (immunostimulation and carrier)
VZV vaccines
1) A live attenuated VZV Oka/Merck strain vaccine is available and is marketed in the United States under the trade name Varivax. 2) In 2006, the United States Food and Drug Administration approved Zostavax for the prevention of shingles. Zostavax is a more concentrated formulation of the Varivax vaccine, designed to elicit an immune response in older adults whose immunity to VZV wanes with advancing age. A systematic review by the Cochrane Library shows that Zostavax reduces the incidence of shingles by almost 50%. US also have an MMRV - like the UK MMR but also contains varicella zoster virus
What are the approaches for SARS-CoV-2 vaccine design?
1) Protein vaccines 2) Inactivated vaccine
Steps of vaccine development
1) Recognize the disease as a distinct entity 2) Identify etiologic agent 3) Grow agent in laboratory 4) Establish an animal model for disease (so you have a model to test your vaccine) 5) Identify an immunologic correlate for immunity to the disease- usually serum antibody (something you can measure so if you have that you know your infected) 6) Inactivate or attenuate the agent in the laboratory- or choose antigens 7) Prepare candidate vaccine following GOOD manufacturing Procedures 8) Evaluate candidate vaccine(s) for ability to protect animals
What are examples of correlates?
Examples of correlates (all correlated with protection for different vaccines for different targets 1) Neutralisation antibody: e.g. polio, measles, rabies 2) Binding antibody (ELISA titres) - e.g. hepatitis A, hepatitis B 3) Other correlates (persistence, ADCC, isotype etc.) - e.g. chickenpox (VZ), rubella
What are virus-like particle vaccines?
- Virus-like particles (VLPs): protein antigen prepared using modern GM, recombinant technology o Capable of assembly into VLPs intrinsically or as part of fusion-protein - Protein can be expressed (in e.g. E. coli, yeast or insect cells) o By itself (requiring adjuvant) or fused to an immunogenic carrier, which may even allow it to assemble into a "virus-like particle" (VLP), e.g. HPV vaccines Gardasil & Cervarix
What are the options for influenza vaccines?
1) - Whole virus inactivated vaccine - Split-virion influenza vaccine: o Treat virus with detergent giving a split virus - Live attenuated influenza vaccine - Subunit influenza vaccine
Conventional linear approach to vaccine development
1) 1% gets through the pre-clinical space into the phase I clinical trials 2) Commercial aspect: Big pharmaceutical companies need to be sure of the return on their investment, whether the vaccine will generate enough money before spending millions to develop a vaccine to a licensed product
What is the timeline for influenza vaccines?
- 1933: IAV isolated and admistered to ferrets. 1930s-1940s: early studies show importance of antigenic matching - 1940s: o 1942 - first clinical trial of inactivated vaccine o 1945: whole virus inactivated vaccine licensed - 1950s: o Egg based technology developed - 1960s: o Split virus vaccines developed in a method safe for children - 1970: o Subunit influenza vaccines based on HA and NA developed - 2003 o First LAIV (nasal spray vaccine) licensed - 2009 o H1N1 pandemic vaccine administered 4 months after pandemic declared - 2012 o Cell cultured vaccines first licensed
HPV vaccine
- HPV vaccine: o Good uptake around the world as it is promoted as a vaccine against cancer - but HPV is an STD - Production o L1 capsid protein produced (different serotypes of HPV) o Purification of L1 capsid protein
How does the HPV vaccine work against HPV?
- How does the vaccine work against HPV? o The HPV major capsid protein L1 can fold correctly and self-assemble into VLPs when expressed in eukaryotic cells. o VLPs aim to protect against the development of cervical cancer; protection would be mediated by the induction of high titres of neutralizing antibodies against the HPV genotypes in the vaccine that prevent the virus infecting the transformation zone, a metaplastic area between the squamous and columnar epithelia in the cervix, where most cancers arise.
Manufacture of influenza vaccines
- Influenza vaccine typically/usually has been grown in eggs - Influenza vaccine is becomingly increasingly produced in cell culture (more formulated fashion)
What are adjuvants
- Protein based vaccines (vaccine that isn't the whole pathogen ) requires an adjuvant - Adjuvant = helps stimulate more of an immune response by causing more inflammation, more antigen is picked up by innate immune resonse and so more of an adaptvei immune response is generated
What is the future potential for influenza vaccines?
- Targeting the HA protein - an anti-stalk vaccine o Chimeric HA vaccine: sequential immunisation with HAS containing identical stalk regions with globular HA head of other influenza virus o Mosaic HA vaccine: sequential immunisation of HAs immunodominant antigenic site on the globular head from other influenza viruses o LAH vaccine: expression of the LAH of HA2 only o Headless HA vaccine: stalk expressed in monomer, trimer or on nanoparticles
Why is it difficult to make an influenza vaccine?
- Three types of influenza: A, B, C o Type A is most dangerous and most complex (H and N on its surface), with 18 different Ha proteins and 11 different Na proteins IAV can make up to 144 different combinations of HA and NA proteins - Antigenic drift of influenzas means that a seasonal influenzas vaccine is required o Vaccine has to be formulated 6 months in advance/before the influenzas season using estimations about the type of virus expected to circulate § Decision has to be made EARLY - as the influenza vaccine production can take time o Most 9/10 predictions for strains to be in the vaccine are correct - COVID-19 will likely become seasonal like influenzas and require seasonal vaccination (for elderly and immunosuppressed)
Effect of an adjuvant for a vaccine
- Vaccines with adjuvants promote the maturation of more APCs, increase the interaction between APCs and T cells, promote the production of greater numbers and more types of T helper-polarizing cytokines, multifunctional T cells, and antibodies, leading to broad and durable immunity, as well as dose and antigen savings
Active immunity
1) Active immunity is protection produced by a person's own immune system. The immune system is stimulated by an antigen to produce antibody-mediated and cell-mediated immunity. Unlike passive immunity, which is temporary, active immunity usually lasts for many years, often for a lifetime. Accquiring active immunity 1) One way to acquire active immunity is to survive infection with the disease-causing form of the organism. In general, once persons recover from infectious diseases, they will have lifelong immunity to that disease (there are exceptions, e.g., malaria). 2) Another way to produce active immunity is by vaccination. Vaccines contain antigens that stimulate the immune system to produce an immune response that is often similar to that produced by the natural infection. With vaccination, however, the recipient is not subjected to the disease and its potential complications.
MMR debate
1) Andrew wakefield published that the MMR vaccine was causing autism in children. But the data was completely flawed and the study involved only a tiny population 2) Lancelet retracted wakefield's article 3) Raised public concern: Diagnosis of autism in children is around the time when the MMR vaccine is given to children (age 2 years) 4) Massive impact on global programme of MMR vaccination
Average to severe SARS-CoV-2 infection
1) Average/healthy individual 2) Impaired immune reponse - viral load is growing faster than immune response = severe disease
Vaccination today vs vaccination in 1960s
1) Balance between risk of vaccine and benefit was less prevalent because the disease was more prevalent. However now the risk of the vaccine/side effects of the vaccine outweighs the prevalence of the disease 2) Developing world will face an increasing problem of vaccinating an increasing population. Increased cost for annual campaign vaccination for babies is going up but not dramatically, no big adjustment to pay for new children as population size increases 3) Using vaccines to protect the individual OR protect the community (without a necessary benefit to individual)
Where do the worst epidemics come from
1) Bats: Ebola, Nipah, SARS-CoV-2 (bats as reservoir host -> intermediate host (pangolin, snakes) -> humans) 2) Lifestock: 2009 swine flu - pigs, Seasonal flu - chickens
What are the 3 commercially available HPV vaccines?
1) Cervarix: 2) Gardasil 3) Gardasil 9
What does global vaccine access depend on?
1) Cost 2) Availability 3) Temperature stability
What are the properties of an ideal vaccine?
1) Efficacy 2) Safety 3) Low cost 4) Potency (preferably as a single dose) 5) Heat stability - from storage into person (if vaccine can be kept stable at room temp then advantageous 6) [Genetic stability - for live vaccines only] 7) Ease of administration - needles and syringes need clinical administration, oral drugs are easier to administer 8) Abundance and availability
What are modern approaches to vaccine development
1) Immunotherapy 2) Adjuvants 3) Synthetic seeds for vaccine production 4) Structural vaccinology - design vaccines at a molecular level (changing parts of genetic code) E.g. RSV (virus) - mainly infects children, Ab against RSV decrease as you get older - grandchildren pass RSV onto grandparents. Vaccine is the spike glycoprotein (target for antibodies), but using structural vaccinology at a molecular level people worked out how to pin the virus into a pre-fusion conformation (this conformation stabilised the glycoprotein and hence prevented the glycoprotein from falling apart 5) Glycoconjugate vaccines 6) Reverse vaccinology 7) Recombinant DNA technology
Inactivated vaccine (2)
1) Inactivated ('killed'/'dead'): virus/antigen preparation chemically treated to inactivate infectivity and toxicity 2) Either inactivated whole virus (rabies), or Subunit (split) vaccines, specific proteins from virus (surface antigen for HBV, HA for influenza), peptides to important epitopes
Classifying vaccines, what diseases they can protect against and when they were first introduced
1) Live attenuated (weakened or inactivated) 2) Killed whole organism/inactivated 3) Toxoid vaccine 4) Subunit, recombinant, conjugate, and polysaccharide vaccines 5) Nucleic acid vaccines 6) Viral vector vaccines
Live attenuated vaccines
1) Live, attenuated form of virulent organism (yellow fever virus, or polio virus - extreme case is variola minor used in 'variolation') 2) Immunologically related, less virulent organism (vaccinia for smallpox) Immune response to a live attenuated vaccine is like that of the natural infection: 1) Attenuated strains continue to replicate giving lifelong immunity, continues to persist and patient can shed these attenuated pathogens for some time 2) Attenuation means the virus or bacterium has been weakened to reduce virulence so it cannot cause disease in healthy people 3) Immune system is constantly being exposed to attenuated pathogen - which maintains a immune response against the pathogen, acts like a natural infection and so elicits a good strong long-lasting immune response
MMR vaccine
1) Measles not eliminated anywhere in the world 2) Measles is easily transmissible Herd immunity is required , an important feature of vaccine-induced protection 1) Herd immunity - infection cannot spread in the population and susceptible individuals are indirectly protected by vaccinated individuals 2) To block transmission of measles need 80% of population to be immunised (so 20% unvaccinated or those immunosuppressed - an unvaccinated person may cause immunosuppressed harm)
Why did poliovirus require a vaccine?
1) Most infections are not problematic - so most cases are asymptomatic 2) Only ~1% of infections lead to paralysis 3) No effective drug treatment 4) Disease is controlled by vaccination 5) Need a trivalent vaccine for the 3 serotypes of poliovirus
Approaches for vaccine design - SARS-CoV-2
1) Multiple technologies, different timeslines, different strengths and weaknesses - race to create a vaccine 2) But SARS-CoV-2 is quite an easy virus to generate a vaccine against
What is the effectiveness of vaccines at preventing SARS-CoV-2 infection?
1) Not necessary to get subsequent COVID boosters if youre a healthy individual 2) Never going to get 80-90% of vaccination coverage globally - never going to get enough herd immunity to protect the vulnerable population against COVID-19 3) More economically to vaccinate the elderly and those at risk (e.g. immunosuppressed) 4) Not everyone in LIC has access to vaccine
What are the two types of methods of accquiring immunity?
1) Passive immunity 2) Active immunity
Vaccine development since the time of Jenner
1) Safety requirements are more stringent (risk/benefit) and acceptability more complex 2) Most new vaccine are intrinsically less immunogenic than whole-cell and/or live vaccines - less immunogenicity means the vaccines are less potent so adjuvants are required to stimulate immune system. Often based on subunits, Need for adjuvants 3) They may contain genetic material, i.e. DNA or RNA , need for special formulations 4) In the future, mucosal vaccines - adjuvants help get the innate immune response working well 5) Vaccines may be tailored for special groups of individuals. E.g. children, elderly subjects, pregnant women, individualized medicine (tumors - making vaccines against tumour Ags)
Problems of using immune globulin:
1) Short lived 2) Serum sickness 3) Immune responses to foreign proteins Solution = can make human Mabs to treat immunosuppressed etc
Vaccination impact
1) So far prevented >3.0 billion disease cases. >500 million deaths 2) 2011-2020 vaccines will prevent: 25 million deaths: 2.5 million/year, 7000/day, 300/hour, 5/min 3) Golden period in 1960s
Subunit vaccines
1) Subunit = purified protein, recombinant protein , polysaccharide, peptide 2) GM Subunit: protein antigen prepared using modern GM, recombinant technology 3) Protein can be expressed (in e.g. E. coli, yeast, mammalian cells or insect cells). By itself (requiring adjuvant) or fused to an immunogenic carrier
What are the types of bacterial inactviated vaccines
1) Suspensions of whole intact killed organisms e.g. whole cell pertussis, i Or 2) Acellular and sub-unit vaccines: Contain one or a few components of organism important in protection E.g. acellular pertussis vaccine contains between 2-5 components of the whole cell pertussis bacteria, e.g. diphtheria toxoid, e.g. Hib polysaccharide
Rabies vaccine
1) The human diploid cell rabies vaccine (H.D.C.V.) was started in 1967. Human diploid cell rabies vaccines are inactivated vaccines made using the attenuated Pitman-Moore L503 strain of the virus. 2) In addition to these developments, newer and less expensive purified chicken embryo cell vaccines (CCEEV) and purified Vero cell rabies vaccines are now available and are recommended for use by the WHO.
How do vaccines work?
1) Vaccine antigen is detected by PRRs on APCs - adjuvant adds to the immunogencity of this vaccine antigen 2) APCs (e.g. dendritic cell) pick up viral antigen (either expressed on cell or present in environment) 3) APCs present this viral antigen on their MHC class II to CD4 T helper cells and MHC class I to CD8 T killer cells 4) CD4+ T cells will signal to B cells, give them helper signal resulting in the proliferation of a b cell with the correct BCR for the viral antigen 5) After clonal expansion of B cells, b cells can differentiate into B memory cells or plasma cells (which produce soluble BCR)
Creating vaccines for new viruses...
1) Vaccines for recent pandemics have been generated (SARS, H1N1 (swine flu), Zika virus) however by the time vaccine is readily available/produced the virus is no longer spreading and is of less concern 2) New vaccines are needed to combat the treat of emerging and re-emerging infections
MMR debate - in depth
1) Wakefield, a surgeon who became a gut expert, first came to public attention in 1998 when he co-authored a study published in the Lancet medical journal. It suggested there was a possible link between rising rates of autism and a bowel disorder in children and the triple measles, mumps and rubella vaccine. 2) He suggested that the MMR vaccine should be 3 separate vaccines - Wakefield said he believed the combination of the three vaccines might overload the body's immune system, leading children to develop the bowel disorder, Crohn's disease, linked to autism. 3) Prior to Wakefield's warning, 91.5% of children in England had the MMR jab by the time they turned two. After the research came out, immunisation rates fell below 80% (need 95% for herd immunity) - between 2000 and 2004 vaccination rates fell 88% to 81% However we have reached 91% measles vaccination in uk 2021 - still 4% of herd immunity Wakefield, 1998
What are some considerations for vaccine development?
1) Which antigens should be used? 2) What type of immunity is needed? Antibody or cell mediated , or mucosal response. Secretory (IgA) or systemic (IgG) antibody 3) When is the immunity needed?: When does the pathogen induce disease? (rubella) Exposure in endemic areas (vaccination before travelling) 4) How should the vaccine be administered?
Severe disease vs no infection
Infection-preventing vaccine: 1) Very hard to generate an infection preventing vaccine 2) Hard to have a strong enough immune response in the upper respiratory tract to kill the virus and prevent infection Disease modifying vaccines: 1) Very successful in reducing symptoms from severe disease to asymptomatic infection
Protein vaccines (1): 1) About 2) Production 3) Examples 4) Advantages 5) Disadvantages
About: 1) Contain proteins from SARS-CoV-2 virus which are recognised by immune system to trigger a response 2) Can be whole proteins, protein fragments of many protein molecules packed into nanoparticles Production: 1) Take spike protein genetic code 2) Genetic code is Inserted into cells 3) Virus protein produced by cells 4) Virus-like particles purified and mixed with adjuvant = vaccine Examples: Ones for COVID-19 are still in clinical trial - e.g. novavax Advantages: 1) High antibody responses 2) Good safety profile Disadvantages: 1) Take longer to make, so less adaptable to variants 2) Requires correct antigen, 3) May need adjuvant and slow manufacture
Inactivated vaccines (2): 1) About 2) Production 3) Examples 4) Advantages 5) Disadvantages
About: 1) Contain the killed SARS-CoV-2 virus, Induce cellular responses to multiple viral proteins, antibody responses lower than for other technologies 2) Many COVID-19 vaccine uses a stabilized version of the viral spike Examples: In clinical trials: shifa-pharmed, chinese academy of medical sciences Advantages: 1) Rapid production 2) The stabilized version may promote the induction of neutralizing antibodies - that provide protection Disadvantages: 1) Risk of enhanced disease: Without stabilization the spike rapidly falls apart, inducing dominant non-neutralizing antibodies. This reduces protective responses and may enhance disease
Nucleic acid vaccines - mRNA (3): 1) About 2) Production 3) Examples 4) Advantages 5) Disadvantages 6) How do they work?
About: 1) Protein antigen expressed from synthetic or from 'self-amplifying' RNA virus replicon-based RNA construct mRNA (either one is directly injected/applied, often in lipid particle to protect RNA and allow uptake into cells) 2) All the technology for mRNA development was in the right place when COVID-19 emerged 3) Need to encapsulate the mRNA Production: (FAST) 1) Start with sequence 2) Order DNA oligomers to assemble into a plasmid 3) Grow plasmid up in bacteria dn tehn purify the plasmid 4) Plasmid used to copy the sequence from DNA to RNA 5) RNA is put into lipid droplet vectors and stored = vaccine Examples: Pfizer/BioNTech and Moderna vaccines Advantages: Safe, better than DNA as no electroporation required don't need to get delivered mRNA into the nucleus Disadvantages: Low cost, fewer antigens than pathogen, mRNA Is very unstable (digested by nucleases etc.) How do they work? 1) mRNA vaccines elicit immunity through transfection of antigen-presenting cells 2) mRNA vaccines translate into antigens that are displayed to T and B cells 3) Both the mRNA and the delivery vehicle enhance the immunogenicity and efficacy of mRNA vaccines
Live recombinant viral vector vaccine (7): 1) About 2) Production 3) Examples 4) Advantages 5) Disadvantages 6) How do they work?
About: 1) Use an unrelated harmless virus, modified to deliverSARS-CoV-2 genetic material (delivery device = viral vector) 2) Our cells use the genetic material to make a specific SARS-CoV-2 protein which is reocognised by immune system to trigger a repsonse Replication-defective recombinant vector: protein antigen expressed from safe, heterologous carrier virus (defectiveness might be partial and/or conditional) Adv: Advantage: as safe as carrier Diasdv: Fewer antigens than pathogen recombination, consumer resistance (?) Replication competent recombinant vector: protein antigen expressed from safe, heterologous carrier virus (or bacteria) Adv: Advantage: as safe as carrier, vector stimulates host responses Diasdv: Fewer antigens than pathogen recombination, consumer resistance (?) Examples: AstraZeneca/Oxford: Saved more lives than any other vaccine as it was made at higher scale at lower cost ($4 a dose). Adenovirus (Carries spike glycoprotein in its genome), gets into host cells and expressed glycoprotein (spike) on surface
Nucleic acid vaccines - saRNA (4): 1) About 2) Production 3) Advantages 4) Disadvantages
About: Synthetic vaccine without the complications of a packaging cell line, contamination with replication competent virus and anti-vector immunity Production: 1) RNA is enzymatically synthesized in vitro from a DNA template 2) RNA is delivered, e.g. in a liposomal formulation, to cytoplasm of host cells 3) RNA self-amplifies in the vaccinee and expresses vaccine antigen (or therapeutic molecule) Advantages: Potentially effective at lower doses than mRNA vaccines Disadvantages: Untested in humans before COVID
Live attenuated vaccines (6): 1) About 2) Advantages 3) Disadvantages
About: Requires viral gene knowledge Advantages: Immunogenic Disadvantages: Risk of reversion to virulent virus
Nucleic acid vaccines - DNA (5): 1) About 2) Advantages 3) Disadvantages
About: protein antigen expressed from DNA plasmid (directly injected, with additives to allow uptake into cells) Advantages: 1) Low cost 2) Additional components in vectors might stimulate host responses Disadvantages: 1) Fewer antigens than pathogen 2) Poorly immunogenic 3) For DNA vaccine to work need to get genetic material into cell and into nucleus (requires electroporation to prevent loss of genetic material at each membrane barrier)
Advantage/disadvantage of inactivated vaccine
Advantage: 1) Safety (as long as the inactivation is complete - disasters with polio [Cutter incident] and FMDV) Disadvantage: 1) Require multiple administration to achieve solid immunity 2) May require adjuvants 3) Protection for shorter duration 4) High cost 5) Reduced cell-mediated immunity
What are the advantages and disadvantages of the HPV vaccine
Advantage: Highly effective if given before sexual debut (prevents acquisition) Disadvantage: 1) Poor or no effect post acquisition (therapeutic) 2) Challenges in global rollout - finance and logistics
What are the advantages and disadvantages of bacterial vaccines?
Advantage: safe but may require carrier and adjuvant Disadvantage: 1) Poorly immunogenic in their own right 2) Often require conjugation to carrier proteins
Disadvantages and advantages of subunit vaccines
Advantage: safety (non-infectious), efficacy Disadvantage: fewer antigens than pathogen - doesn't have as many targets as the whole virus/bacteria itself (focusing immune rsonse only on one thing)
Examples of pathgoens for which attenuated vaccines are used for?
Virus: Oral polio, measles, mumps, rubella, yellow fever Bacteria: BCG, cholera
Advantages and diasdvantages of live attenuated vaccines
Advantages: 1) Local and systemic immunity produced 2) Low cost and ease of manufacture and administration 3) Single dose often sufficient to induce long-lasting immunity 4) Strong immune response evoked (induces both T cell and antibody responses) Disadvantages: 1) Heat lability 2) Virus may be shed into the environment 3) Takes long time to develop a pathogen to be attenuated enough to be SAFE to put into human (normally put into animals first) 4) Potential to revert to virulence (could cause serious infection in immunosuppressed) 5) Contraindicated in immunosuppressed patients 6) Interference by viruses or vaccines and passive antibody 7) Poor stability in liquid form 8) Potential for contamination
Polio eradication
Areas in world that are 'hard' to access/reach: 1) Geoegraphically 2) Politically unstable 3) Suspicision against manufacture in first world countries Serotypes: 1) PV2 WT serotype: Declared eradicated 2015 (last detected 2012) 2) PV3 WT: Declared eradicated 2019 3) Vaccine now only bivalent (against 1 and 3) 4) Recent cases/report: Only one WT poliovirus case in Pakistan in 2021 and only one WT case anywhere so far in 2022 (Afghanistan). Hard to eradicate all of polio every single case. Vaccine derived polio cases are still occurring
What are the two outcomes of a b cell in the germinal centre
B cell with a BCR with LOW affinity = no TFH help/signal = death (apoptosis) B cell with a BCR with HIGH affinity for antigen = TFH signal = survival and production of antibodies (with this antigen affinity). B cell will process antigen (if its antibody receptor has some affinity for the Ag), and present antigen to CD4+ T cell (follicular helper cell). The result is production of affinity matured antibodies
What are the problems with generating bacterial vaccines?
Bacteria are covered in polysaccharides, antibodies don't make good responses to these sugars and no T cell response is generated either
What are correlates?
Correlates: An immune marker statistically correlated with vaccine efficacy (equivalently predictive of vaccine efficacy) that may or may not be a mechanistic causal agent of protection
How accelerated was the vaccine development for SARS-CoV-2?
Didn't not do any of the stages in vaccine development - safety wasn't compromised 1) Pre-clinical testing for testing antigens and adjuvants was done on animal models. This normally takes 5-10 years but only took weeks-months for SARS-CoV-2 2) Clinical testing involving: Phase I trials: normally takes 3 years - took only 3 months for SARS-CoV-2 Phase II trials: normally takes 3 years - took only 3 months for SARS-CoV-2 Phase III trials: normally takes 3 years - took only 6-12 months for SARS-CoV-2 3) Monitoring - phase IV: mass vaccination
What are the generations of live attenuated vaccines?
First-generation - live attenuated 1) The first-generation vaccines are manufactured by growing live vaccinia virus in the skin of live animals (cows, sheep) 2) The development of freeze-dried vaccine in the 1950s made it possible to preserve vaccinia virus for long periods of time without refrigeration (scarification with bifurcated needle, significant side effects) Second-generation - live attenuated 1) The second-generation vaccines consist of live vaccinia virus grown in eggs or cells (MRC5 or Vero cells) allowing for vaccine production in a sterile environment 2) (While first-generation vaccine contains skin bacteria from the animal that the vaccine was grown on) The third-generation vaccines 1) Based on attenuated vaccinia viruses that are much less virulent and carry lesser side effects. The attenuated viruses may be replicating or non-replicating. 2) Understanding pathogen at molecular level and modification of pathogen at molecular level = even safer vaccine 3) Modified vaccinia Ankara (MVA, German: Modifiziertes Vakziniavirus Ankara) is a replication-incompetent variant of vaccinia
What are examples of polysaccharide and protein-polysaccharide conjugate vaccines?
Haemophilus influenzae type b vaccines 1) Polysaccharide vaccines for Haemophilus influenzae type b (Hib) were first used in 1985 but were rapidly replaced in 1989 by protein-polysaccharide conjugate vaccines containing the Hib polysaccharide chemically conjugated to a protein carrier, such as diphtheria toxoid, tetanus toxoid or meningococcal outer membrane protein. 2) These vaccines continue to be widely used, mainly among preschool children. Pneumococcal vaccines 1) A vaccine containing 14 different polysaccharides from Streptococcus pneumoniae was licensed in the United States in 1977 and was replaced by a 23-valent vaccine in 1983 for the prevention of pneumococcal disease in the elderly. 2) A protein-polysaccharide conjugate pneumococcal vaccine containing seven serotypes was first used in the United States in 2000 (and in the United Kingdom in 2006). 3) In this vaccine, the carrier protein is cross-reacting material 197 (CRM197; which contains a glycine to glutamic acid point mutation at position 52 in the A subunit of diphtheria toxoid). Meningococcal vaccines 1) A quadrivalent meningococcal vaccine containing serogroup A, C, Y and W135 polysaccharides of Neisseria meningitidis was first licensed in the United States in 1981, and a bivalent A plus C vaccine is also available in some countries. 2) Serogroup C (MenC) conjugate vaccines were first used in the United Kingdom in 1999 (conjugated to either tetanus toxoid or CRM197), and a quadrivalent A, C, Y and W135-diphtheria toxoid conjugate vaccine has been available in North America since 2005.
How was the vaccine for SARS-CoV-2 made so quickly?
Huge amounts of money/finance was available High demand for big pharmaceutical companies to develop vaccines, with governments paying big companies to develop vaccines
Advantages of passive immunity
Immediate protection
Immune repsonse and possible vaccine/treatments for COVID-19
Immune response: 1) Upon infection patient will have T cell responses against other components of virus - if glycoprotein changes you will still get infected but LESS likely to get sick 2) Will start to see more variants (like common colds - superficial infection but not that unwell) in healthy individuals adult population 3) High enough Ab in upper airways may block transmission, but preventing infection of the lower airways is more important in preventing hospitaliation
Founder of vaccinology
Live attenuated vaccines were the first vaccines - first introduced in 1798 (smallpox) 1) Before vaccinaton = variolation. 17ce 'variolation' by which pus is taken from a smallpox blister and introduced into a scratch in the skin of an uninfected person to confer protection (Lady Montague). Smallpox killed over half a billion people in the 20th century alone — three times the number of deaths from all of the century's wars combined. 2) Edward jenner: On 14 May 1796, Jenner inoculated 8-year-old James Phipps with cowpox lesion material from milkmaid Sarah Nelms. 3) Jenner faced criticism: Jenner was REJECTED for his beliefs, many people were making money from variolation against smallpox. Injecting of 'cow' unfavourable in opinion 4) Smallpox was declared eradicated by the World Health Organization in 1980
Primary vs secondary immune responses - attenuated vaccine
Not always the case - an attenuating vaccine (a pathogen that is attenuated, doesn't cause disease), because this pathogen is persisting it will do both these things Attenuated vaccine e.g. measles mumps - long lived antibody response which stays above protective threshold 1) Favourable lifelong protective antibody levels after first vaccination (initial primary immune response) 2) Vaccine only required ONCE = ideal
What are the objectives of vaccination?
Objectives of vaccination: Protection against infection, disease or both? 1) Protect the vaccinee (most vaccines) 2) Protect the foetus (e.g. rubella) 3) Protect the neonate (e.g. porcine rotavirus, [whooping cough]), Maternal antibodies can inhibit live attenuated vaccines e.g. measles given to infants too soon 4) Protect the community; "altruistic vaccines". Many vaccines offer benefit of "herd immunity" but it is the major objective of recently-introduced vaccination of infants using live, attenuated "Flu-Mist" influenza vaccine
Passive immunity
Passive immunity: 1) Passive immunity is protection by antibody or antitoxin produced by one animal or human and transferred to another Forms of passive immunity: 1) Immune globulin (rabies and infants born to HBV +ve mothers): Immune globulin products from human sources are primarily polyclonal; they contain many kinds of antibodies. E.g. Rabies: passive immune globulin treatment used to involve the transfer of Ab from animals infected with pathogen purifying this Ab and injecting into human 2) Maternal antibodies: The most common form of passive immunity is that which an infant receives from the mother. Antibodies, specifically the class of antibody referred to as IgG, are transported across the placenta, primarily during the last 1 to 2 months of pregnancy. As a result, a full-term infant will have the same type of antibodies as the mother. These antibodies can protect the infant from certain diseases within the first few months after birth. 3) Monoclonal antibodies: recombinant monoclonal antibodies. Monoclonal antibodies are better than immune golbulin as Mabs only target a specific antigen. New lease of life as recombinant, humanised Mabs (e.g. Zmapp plantibody produced in tobacco against Ebola virus, Regeneron's 'REGN-COV2' cocktail)
Examples of pathogens for which killed/inactivated vaccines are used for?
Polio, influenza, hepatitis A, rabies
Main principles of vaccination
Presentation to the immune system of pathogen "antigen(s)", or just "peptide epitopes", in a SAFE form 1) Antigens may be pre-produced or "expressed" in the body from "vectors" 2) Immune system has been prepared in order to raise a more rapid immune response, or have an immune response at a significant magnitude that it prevents infection or disease (most vaccines prevent DISEASE not infection, wont realise you will have seen that virus) Stimulation of the innate immune system, which recognises infection non-specifically (encoded in germline - use PRRs to detect PAMPs, no lifelong immunity), so that it will activate the acquired/adaptive immune system to proliferate b/t cells and lay down memory cells = lifelong memory of pathogen antigen 1) "Trick" the innate immune system that the body is under threat 2) Requires "danger signals" Provided intrinsically by intracellular replication of live, attenuated virus vaccines OR Provided extrinsically as adjuvants, including components of pathogens (LOOK UP "Freund's adjuvant"), alum or lipids OR Provided extrinsically or intrinsically as components of the host pathways that signal "danger", so that those pathways are switched on
How can you get a good immune response from a bacterial vaccine?
Protein-polysaccharide conjugate: protein carrier (to get T cell help) resulting in antibody production Examples = haemophilius influenzae type B, pneumococcal, meningococcal, typhoid vaccine Outer membrane vesicle - pathogen antigen on surface of a gram negative bacterial outer membrane 1) Easier to make than a protein polysaccharide conjugate 2) ADV - broader immune response 3) E.g. group B meninococcal
What are the different vaccines introduced for polio?
Salk vaccine (1955) 1) Salk developed his inactivated 'killed' polio vaccine by growing the virus in monkey kidney cells, then killing the virus with formalin. 2) IPV - injectable polio virus vaccine Sabin vaccine (1963) 1) Live attenuated virus vaccine developed after multiple passage in tissue culture - infectious for the gut, but devoid of neurovirulence 2) Studies of reversion in 1980s elucidated mechanisms of reversion, public confidence maintained 3) As eradication achieved regionally (and approached globally), need to transfer to use of killed vaccine to prevent generation and possible circulation of virulent virus 4) OPV - oral polio virus vaccine
Advantages and diasdvantages for each type of polio vaccine
Salk vaccine - advantages 1) No risk of infection 2) No reversion - assuming virus has been properly inactivated Salk vaccine - disadvantages 1) May carry live virus (inactivation wasn't always successful) - not really a problem after the cutter incident 2) Little intestinal immunity (virus does not replicate - so don't get as good intestinal immunity, so not getting T cell immunity - not getting all the types of immunity) 3) Cost 4) Safety (syringe use) - re-using of syringes and needles resulted in HIV etc. 5) Injections - ouch! Sabin vaccine - advantages 1) Oral delivery - easy to administer (sugar cube) 2) Cheap 3) Replicates in the intestine - good mucosal immunity 4) Easier to achieve passive/herd immunity Herd immunity - achieved because vaccinees will shed the virus for 3 months and can pass it on to non-vaccinees. However, this route of transmission all entails a risk of a real infection due to reversion Sabin vaccine - disadvantages 1) Vaccine virus is shed in stools up to 3 months post inoculation 2) Reversion to virulence may occur - vaccination may cause paralysis 1 in 530,000 in first time vaccinees 1 in 12 million for subsequence vaccinations 3) OPV no longer used in UK - to dangerous to give OPV to children due to reversion and paralysis (but US use salk vaccine for first two vaccinations then OPV)
Primary vs secondary immune responses - typical vaccine
Secondary immune response is FASTER and HIGHER than primary immune response 1) Memory cells/response is generated after first primary immune response enabling upon second exposure to pathogen , a faster and bigger secondary immune response (antibody titre increases more quickly and more greatly) 2) Antibody titre doesn't remain above protective threshold First vs second dose: 1) First dose: igM produced first but declines. IgG produced subsequently but declines 2) Second dose: IgM response similar to first dose. IgG response is bigger and the affinity of that antibody for antigen is stronger
Two key events that occur in the germinal centre
Somatic hypermutation 1) B cells acquire increased affinity for foreign antigens through somatic hypermutation (SHM) of their immunoglobulin variable-region genes. 2) Occurs in DARK zone Affinity maturation: 1) Positive selection of B cells with increased affinity for foreign antigens on the basis of enhanced CD4 T cell help 2) After entering the light zone, the high affinity GC B cells gain preferential access to foreign antigens that are expressed on the surface of follicular dendritic cells 3) The specific provision of T follicular helper (TFH) cell-derived helper signals to high-affinity GC B cells is proposed to be one of, if not the only, major drivers of antibody affinity maturation 4) Many variations of antibody are being produced, the b cell with the highest affinity for antigen will scrape off more antigen and present to the T cell and get the MOST help - Darwinian selection. Over time this antibody affinity grows with immune response
Start of the COVID-19 pandemic
Start of pandemic: 1) Patient zero - his symptoms started on 1 December in Wuhan China - could be earlier. 2) First sequence identified 24th December - China made sequence available globally very fast. Communication globally allowed scientists to work on developing vaccines using this sequence 3) Rapid spread around the world (even with lockdowns in Wuhan at time virus emerged) Global situation - 2023 1) 809 vaccine doses have been administered 2) 6, 961, 014 deaths 3) More infections and less deaths after vaccine produced Vaccine Spike glycoprotein binds to ACE2 receptor - can generate antibodies against the glycoprotein to block infectious process
What is the basic reproductive number (R0)?
The basic reproductive number (R0) represents the mean number of secondary cases that are expected to arise if an infectious individual is introduced into a completely susceptible population and is an important metric to compare the contagiousness of measles virus (MeV) to other viruses. The estimated R0 for MeV is 9-18, which contrasts with only 5-7 for smallpox virus and 4-13 for polioviruses.
