New versions of the H5N1 virus are increasingly adept at spreading. Suggestions to either let it rip in poultry or vaccinate the birds could backfire.

Flu Shot in Pregnancy Tied to Fewer Infections in Young Infants — Protection appeared greatest when vaccination occurred in the second or third trimesters ...

The Food and Drug Administration on Wednesday approved a twice-yearly injection that provided a near-perfect shield against H.I.V. infection in clinical trials. The approval is among the most ...