Tackling common vaccine questions

How are vaccines tested, and do they have side effects?
21 May 2019

Interview with 

Clare Bryant, University of Cambridge


a scientist at a lab bench with samples


Adam Murphy and Izzie Clarke went back to immunologist Clare Bryant to ask her some common questions people have about vaccines. Starting with how vaccine schedules are decided...

Clare - There were three important factors to consider when designing vaccine schedules and these are thought about very, very carefully by the companies when they're making the vaccines. First of all, when you're a child you're born with antibodies which come from your mother and they drop over time so your protection against disease that is conferred by these antibodies, begins to disappear. And you need to have got rid of those antibodies in order for your own antibodies to be made in the body. But in order to make your own antibodies you also need to have your immune system to be competent, so it's a balance between getting rid of the antibodies from the mother and having your own immune system sufficiently active that you can generate your own antibodies. So those two factors are very important.

And then the third factor that's really important is when is a child most likely to encounter the disease; in other words when is the child at most risk. So there's those three factors are all calculated in when you're thinking about designing a schedule for vaccination for your children.

Izzie - We come across combination vaccines, so why are there combo vaccines and how are they tested?

Clare - Vaccines are all tested the same way. It's absolutely critical that a vaccine is safe and any vaccine that produces any kind of severe side-effect is never taken to market. And also this is tested afterwards so any vaccines that appear to induce some kind of effects postmarketing and post being released onto the market is actually taken out if there's any kind of severe side effect. So that's the first thing to say, there's a lot of testing involved.

Combo vaccines tend to be now vaccines that are important for childhood diseases - measles, mumps, rubella, for example, which will contain a mixture of live attenuated vaccines. We know that the children suffer from these diseases at a particular time in their life, all around the same time in your life so that's when a combo vaccine is produced. And testing schedules over the years have shown that actually you can give a combination of these vaccines together and they don't actually cause any detrimental effects to the children. So you're really being able to immunise against a number of diseases all at the same time, which is the most efficient way to go.

It is important to state that when you are testing for vaccines, particularly with combination vaccines or any vaccine actually, but combination vaccines are tested all altogether so that's a very, very important part of the safety regime.

Adam - Are there side-effects to vaccines?

Clare - Yeah, there can be side-effects to vaccines. And it's specific to each vaccine as to what the side effects can be. So if you're giving an attenuated vaccine you're giving a low dose of the disease so you can sometimes get side-effects such as fever, which is the common sort of thing you'll get with an infection. Some of the vaccines will have side-effects such as sore arm which you get sometimes with tetanus. These effects are relatively minor but they are quite common and they're very well documented.

Anything more severe than that takes the vaccine out of the market, but there is one exception to that. Anything that's made in an egg, if you're allergic to egg derived proteins then you can have a severe anaphylactic reaction by which I mean a very severe allergic reaction to vaccines made in egg. So under those circumstances those vaccines shouldn't be used in people that are allergic to eggs. But generally, the side-effects are really very, very carefully balanced and carefully tested for and considered relatively low grade.


Add a comment