First CDC signed off on a COVID-19 vaccine for adults, then teens. Now US children ages 5 to 11 are officially eligible for shots. Here’s the science on why each group needs to be considered separately.

It's normal for different people to mount stronger or weaker immune responses to a vaccine, but post-shot side effects won't tell you which you are.

Older coronavirus patients face grimmer outlooks. A virologist explains the aging-related changes in how immune systems work that are to blame.

If antibody levels drop dramatically after an infection, what does that mean for immunity? An expert explains how B and T cells contribute to immunity and why antibodies don't tell the full story.

Researchers discover clues to the origin of inflammatory bowel disease and a possible strategy for treatment.