Q and A


Why doesn’t everyone get the COVID-19 vaccines that are 95% effective?


I see that some vaccines are better than others. One might be 95% and another 70% and I don’t know why we don’t all use the best one?




Thanks, this is something we get asked a lot. You are right that it seems a good idea to just use the one with highest efficacy. This percentage though is not the only thing that is important. It might not even be the most important.

Other important factors include:

  • Effect against variants.
  • Effect in different populations.
  • Storage and transportation.
  • How long the protection lasts.

Each study was carried out at a certain time and place. Participants can also be very different.

For example, early studies were carried out before the new variants. Later studies will be tested against the more aggressive variants were around.

Or differences related to age. Older age is one of the most important risks for COVID-19. Studies in younger people will have fewer infections. But a study with more people older than 65 might actually be more effective, even if the percentage is lower.

Vaccines also make two types of immune response. The one measured in vaccines studies prevents early symptoms. The other though prevents severe outcomes.

Also, the top-line result relates to protection from COVID-19 symptoms. Actually, the most important result is whether the vaccine prevents the most serious events including death. Luckily, all the current vaccines are effective at stopping these most serious outcomes.

Then there are practical issues. How many shots are needed? How easy they are to store and transport? In some countries and regions, refrigeration to really low temperatures is difficult. Having a single shot vaccine makes a big difference to population health.

Finally, how long does vaccine protection last? Vaccines that have a slightly lower efficacy, might have much long protection.

In summary, the percentage misses out lots of things that might be more important.

But, all the currently authorised vaccines are highly safe and effective. Second-generation vaccines are already in studies to provide broader protection against variants.

This is why the UK recommends all HIV positive people can use the first available vaccine. We can then use different boosters in the future to cover variants.


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