Erin Kissane, a co-founder of the COVID Tracking Project, rolled up her sleeve for the Novavax Covid-19 vaccine in mid-October soon after it was finally recommended in the United States. Like many people with autoimmune diseases, she wants to protect herself from a potentially devastating Covid infection.

Kissane’s autoimmune arthritis seems to make her susceptible to unusual vaccine side effects. After getting an mRNA booster last year, her joints ached so painfully that her doctor prescribed steroids to dampen the inflammation. She still considers the mRNA vaccines “miraculous,” knowing Covid could be far worse than temporary aches.