Question: How do scientists know how to make a flu vaccine if viruses can be different every year?

Sive Finlay answered on 13 Nov 2013:

Hi Eamoo,

Great question! You’re right that viruses are changing all the time so it can be very difficult for people who design and make vaccines to keep up. There are scientists who specialise in using computer models to try to understand and predict the evolution of viruses. They study the changes which viruses have gone through in the past and then use that information to try to predict how the virus is going to change in the future. The World Health Organisation collects information on which flu viruses are circulating in populations at the moment and combines that with the models that predict how the viruses might evolve and also which strains of virus are most likely to infect the majority of the population. New vaccines are then designed based on this information. There can be a big variation in which strains of flu virus are found in different areas so each country decides which types of vaccine to give to their own population.
So really it’s all a big guessing game based on gathering as much information as possible. Vaccines have to be made in advance of the flu season when they’re actually needed so scientists and health experts have to do their best to predict which viruses are going to be the most common and how those viruses might change in the coming months. It doesn’t always work; some years flu vaccines are more effective than others, but as we get more information and experience with understanding how viruses evolve then hopefully we’ll get even better at keeping away the flu!
Sive