Vaccine Development: A Chronology

Vaccine development and usage over the past couple of decades has significantly reduced the number of infections and diseases affecting us today. As you will see, vaccine development is a difficult, complex and highly costly multi-step process that has saved numerous lives over the years.

The first-ever vaccine was developed, against smallpox, in England by Edward Jenner in 1796 [1]. Since his discovery, smallpox has been eradicated. Although his methods of recruitment would never pass any ethics board today, his work is regarded as the foundation of immunology [1]. Vaccine development has since changed quite a lot and has also become increasingly consensual.

A number of key issues need to be addressed to establish that a vaccine candidate has the desired properties.⁣⁠

It is only after a vaccine passes all safety and efficacy tests that it receives regulatory approval to enter the markets commercially.

Preclinical Research: ⁣⁠
The goal of preclinical research is to test a new vaccine product to demonstrate its suitability for use in humans. Preclinical research and development are carried out in the laboratory using in vitro techniques (studies are carried out in cell lines). At this stage, various checks are undertaken to ensure the vaccine candidate produces the desired effects in vitro (i.e. in cells in a petri dish). This stage involves studying the characteristics of the vaccine in development, indicators of safety and immunogenicity tests. This step must also include details of the development and production of the vaccine, which should be adequate to justify subsequent clinical trials in animals and humans [2].⁣⁠

At the Preclinical Stage of Vaccine Development, various checks are undertaken to ensure the vaccine candidate produces the desired effects in vitro (i.e. in cells in a petri dish)

Animal Studies: ⁣⁠
The animal studies must show that the vaccine candidate elicits the desired immune response. It also needs to protect animals against the disease the vaccine is intended for. Side effects of the vaccine are also studied here – for the vaccine to go through to human trials, it should be relatively free of side effects. The vaccine developer must also demonstrate that the vaccine can be produced in a consistent matter [3].⁣⁠

Animal studies must show that the animals are protected against the disease vaccinated against. For example, the vaccinated rhesus monkeys in the COVID-19 trials must not be infected when exposed to the SARS-CoV-2 virus.

Clinical trials in humans are classified into three phases: Phase I, Phase II and Phase III studies [2]. ⁣⁠
Phase I: ⁣⁠
A phase I studies generally includes fewer than 100 healthy volunteers. Here, escalating doses of the candidate vaccine are administered to study the properties of the vaccine, tolerability and other parameters concerned with safety [2, 3]. Phase I is considered successful if it demonstrates that the vaccine candidate is well tolerated or identifies any immediate safety concerns that will need to be closely monitored in future clinical studies [3]. Phase I studies also provide an initial indication of the optimal dose and number of doses required.⁣⁠

Phase I studies generally includes fewer than 100 healthy volunteers. Different doses of the experimental vaccine are administered to study safety and efficacy.

⁣Phase II: ⁣⁠
A phase II trial typically involves a larger number of subjects. Phase II studies provide additional safety data as they are tested on a larger number of individuals of the target population [3]. Immunological responses are also measured to ensure that vaccine recipients are at a decreased risk of infection/disease compared to the placebo group. Vaccines that produce a tolerable immunogenic response and show protective properties in recipients, can then advance to the next phase [3]. ⁣⁠

Phase II studies typically involve a larger number of volunteers from the target population i.e. the population the vaccine is being developed for. This could be kids, adults, or the elderly. This phase provides additional safety data.

Phase III: ⁠⁣⁠
Phase III studies include 10,000+ subjects [2]. This allows for the identification of rarer adverse effects, the establishment of definitive evidence of protective efficacy, and the establishment of the clinical consistency of the vaccine [3]. At the end of Phase III, the vaccine is released into the market for use by patients, barring regulatory approval by the FDA and the likes.⁠⁣⁠

A phase III trial recruits 10k+ subjects to identify rarer side effects, should they occur. If a vaccine passes this phase, it can be released into the market barring regulatory approval by the FDA.

⁠⁣Phase IV:⁠⁣⁠
Following the market release of the vaccine, Phase IV studies are a form of surveillance platform to track adverse effects [3]. The long-term efficacy of the vaccine is continually studied.⁠⁣⁠

Phase IV studies are a surveillance platform to track adverse effects after the vaccine is approved for use commercially.

Questions on vaccine development are now very frequent, given the pressure the COVID-19 pandemic has put on healthcare systems around the world. If you want to know more about the top COVID-19 vaccines, please do have a look at some of our previous posts. We have previously written posts on the Moderna vaccine, the Oxford/AstraZeneca vaccine, the CoronaVac developed by Sinovac, and the vaccine developed by Novavax.

Should you have any questions about vaccine development, or the COVID-19 vaccines, please do not hesitate to leave us a comment down below.






36 Replies to “Vaccine Development: A Chronology”

  1. Reblogged this on Fancy Comma, LLC and commented:
    Great post by The Shared Microscope about the clinical trials process and how each step works. Everyone should know about clinical trials in the era of COVID-19 so that they can keep tabs on when potential therapeutics and vaccines may be made commercially available.

    Liked by 1 person

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