The president should keep his promise on vaccine patents.
The most common questions about vaccination side effects, answered.
Reports of reinfection instead may be cases of drawn-out illness. A decline in antibodies is normal after a few weeks, and people are protected from the coronavirus in other ways.
A company that makes internet-connected thermometers has followed the flu more closely than the C.D.C. can. Now the devices may be turning up cases of Covid-19.