How are vaccines developed anyway?
What’s up with vaccine development? What do the different stages mean and how do they test them? I know that vaccines aren’t dangerous, but...how do we actually know?
All vaccines, not just COVID, go through a very specific process of development. It’s the same across countries, companies, and research teams. Here’s what it looks like:
Early development. Looking at what we can learn from existing vaccines, considering what kinds of approaches could be used.
Laboratory testing. Once a vaccine candidate is found, it goes through laboratory testing. First “in vitro'' testing, which means looking at individual cells and cellular responses. Then “in vivo” testing, - testing in a living being - which generally involves mice. There is a lot of safety testing here, to make sure the vaccine isn’t harming the animal subjects. If it’s safe and it works in animals, then the vaccine candidate goes to a Phase 1 study.
Phase 1 A phase 1 study involves testing the vaccine in a small group (100 or less) of adult volunteers. It monitors them closely for safety and for side effects. It is also designed to find the most effective dose level for producing an immune response in humans.
Phase 2 A phase 2 study brings the number of participants up to several hundred people. It checks to see if the vaccine consistently produces an immune response in vaccinated people. This larger group lets researchers look for rarer side effects.
Phase 3 This is where things get serious. Phase 3 requires a big study size - several thousand people at least. And in addition to checking whether the vaccine produces an immune response in people who’ve been vaccinated, it checks whether vaccinations actually reduce the spread of the disease. This is where malaria vaccines have historically run into trouble, and we’ve seen with COVID vaccines that they’re losing their ability to stop the spread of the disease.
Licensing Go time! If a vaccine passes Phase 3, then it can be evaluated by government regulators, licensed, and brought to market. People then start getting vaccinated.
Phase 4 Once the vaccine is in regular use, we still pay attention. First for safety reasons, to uncover allergic reactions or side effects. And secondly to track the epidemiology - is the vaccine continuing to reduce transmission? Severity of disease? Hospitalization rates in infected people? The phase 4 data is used to improve the vaccine and inform the development of other vaccines in the future.
Next week I’ll talk about the COVID vaccine and how we developed it so fast.
This post is a response to a question from a paid subscriber