I put together an infographic to help parents understand and talk with their children about the possible side effects. Not surprising that pain at the injection site was the most common side effect. Fatigue and headache followed.
Swelling at the injection site was much higher in vaccine than placebo — that is also expected. The vaccine will trigger an immune response, and swelling at the injection site is just the immune system responding to the vaccine. So, it’s completely expected.
By the way, when I look at side effect (or even treatment effects) I always look at it in the context of the placebo response. It is important to be able to compare the responses between treatment and placebo to see what may just be a result of injection, and not necessarily a vaccine response.