Why different immune responses among different individuals against COVID vaccine?

The Oxford vaccine trial at the centre of safety Concerns this week highlights the idea that people's immune systems respond to vaccines differently.

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We don't yet know whether reports of immune complications in one or two trial participants have been linked to the COVID-19 vaccine itself, or if they were given the placebo vaccine.

But it does highlight the importance of phase 3 clinical trials in many thousands of people, across continents. These not only tell us whether a vaccine is safe, but also whether it works for people of different ages or with particular health issues.

So what are some of the immune factors that determine whether any of the 180 or so COVID-19 vaccine candidates being developed around the world actually work?

Our immune responses are all different

An effective vaccine should generate long-lasting protective immunity against SARS-CoV-2, the virus that causes COVID-19.

This can be by generating antibodies to neutralise the virus and likely also by helping the immune system memorise and quickly respond to infection.

We know, from developing vaccines against other viruses, that people's immune response to a vaccine can vary. There's every reason to believe this will also be the case for a COVID-19 vaccine.

Dr Paul Gill, Postdoctoral Researcher (Gastroenterology and Immunology), Monash University, Melbourne, Australia.

Menno van Zelm, Associate Professor, Immunology, Monash University, Melbourne, Australia.

1. Vaccine type and how it's delivered