White blood cells swarm to the site, prompting inflammation that’s responsible for chills, soreness, fatigue and other side effects.
This rapid-response step of your immune system tends to wane with age, one reason younger people report side effects more often than older adults.A tiny percentage of people who got vaccines made by AstraZeneca and Johnson & Johnson reported an unusual type of blood clot.
That’s why you’re asked to stick around for about 15 minutes after getting any type of COVID-19 vaccine — to ensure any reaction can be promptly treated