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Here is what scientists know about the risk of breakthrough Covid deaths.

Multiple myeloma is a rare cancer that seems to strike at random.

If You’ve Had Covid, Do You Need the Vaccine?

Covid toes’ may be caused by an immune system overreaction, a new study finds.

Moderna vs. Pfizer: Both Knockouts, but One Seems to Have the Edge

In a new review, some F.D.A. scientists and others say boosters aren’t needed for the general population.

Second Dose of J. & J. Vaccine Gives Strong Boost, Company Reports

Second Dose of J. & J. Vaccine Gives Strong Boost, Company Reports

Vaccine Effectiveness Against Infection May Wane, C.D.C. Studies Find

The World Health Organization is testing three more drugs in a broad search for Covid treatments.

What to Know About Breakthrough Infections and the Delta Variant

F.D.A. Aiming to Speed Extra Vaccine Doses for Immunocompromised Patients

F.D.A. Aiming to Speed Extra Vaccine Doses for Immunocompromised Patients

Behind the Masks, a Mystery: How Often Do the Vaccinated Spread the Virus?

One Dose of J.&J. Vaccine Is Ineffective Against Delta, Study Suggests

You’re Missing Microbes. But Is ‘Rewilding’ the Way to Get Them Back?

Citing the Delta Variant, Pfizer Will Pursue Booster Shots and a New Vaccine

How does the Delta variant dodge the immune system? Scientists find clues.

Johnson & Johnson Vaccine Protects Against Delta Variant, Company Reports

Three Studies, One Result: Vaccines Point the Way Out of the Pandemic