Lecturer of Immunology, Cardiff Metropolitan University
There are many reasons your immune system might react differently to vaccines.
Most vaccines have side-effects and COVID vaccines are no different. The public are being reassured that if they experience a sore arm where the needle went in, or tiredness, a headache, fever or nausea, these are merely signs that the immune system is working as it should. This has left some people wondering: if that’s the immune system doing what it’s supposed to do, does a lack of side-effects mean my immune system hasn’t been primed to protect me?
Rest assured, it means no such thing. The vaccine clinical trials conducted by Pfizer show that 50% of the participants did not experience significant side-effects during the trial, yet 90% of the participants developed immunity against the virus. And the advice on the Moderna vaccine says that common side-effects may be experienced by one in ten people, yet the vaccine protects 95% of those who take it.
This can be explained by considering the way the immune system develops protective immunity against viruses when triggered to do so by a vaccine. Most COVID vaccines, including several that have been authorised, use a viral protein found on the outer envelope of the coronavirus, known as the spike protein, to mimic a natural viral infection and initiate an immune response.
The branch of the immune response known as innate immunity responds almost immediately to the viral spike protein. It launches an attack against it by initiating inflammation, the cardinal signs of which are fever and pain. So it’s the innate immune response that causes the common side-effects that people experience a day or two after they’ve had the jab.
ong-lasting specific immunity, which is the ultimate goal of any vaccination, is achieved only by activating the second branch of the immune response: adaptive immunity.
Continue reading: Why some people don’t experience vaccine side-effects, and why it’s not a problem
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