The U.S. Is Getting a Crash Course in Scientific Uncertainty

As the pandemic takes an unexpected direction, Americans again must reckon with twists in scientific understanding of the virus.

Maker of Popular Covid Test Told Factory to Destroy Inventory

One of the leading producers of rapid tests purged supplies and laid off workers as sales dwindled. Weeks later, the U.S. is facing a surge in infections with diminished capacity.

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

Federal health officials said the new data justified a campaign of booster shots. But some scientists disagreed, saying not every American needs another dose.

Vaccines’ protection against virus infection is waning, C.D.C. studies suggest.

Some scientists pushed back, saying the new research does not indicate that all Americans need boosters, as federal officials have said.

In a Handful of States, Early Data Hint at a Rise in Breakthrough Infections

With the arrival of the contagious Delta variant, Covid hospitalizations and deaths among vaccinated Americans also may have increased, according to preliminary figures.

C.D.C. Panel Recommends Third Dose of Covid Vaccine for Immunocompromised

A day after the F.D.A. authorized third doses of the Pfizer-BioNTech and Moderna vaccines for some immunocompromised people, an independent expert panel advising the C.D.C. recommended the move.

Why Not Just Tell Everyone to Wear Masks?

The C.D.C.’s advice about masking up again was not easy to parse. Some experts think simpler would have been better.

What to Know About Breakthrough Infections and the Delta Variant

Scientific understanding of the coronavirus variant is changing quickly. Here’s a recap of the most important findings.

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

Worried about a vulnerable population as the Delta variant surges, administration officials are taking a new tack.

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

Worried about a vulnerable population as the Delta variant surges, administration officials are taking a new tack.

Nursing Homes Confront New Covid Outbreaks Amid Calls for Staff Vaccination Mandates

With the vaccinated elderly susceptible to breakthrough infections, inoculation of workers is becoming more urgent.

F.D.A. Aims to Give Final Approval to Pfizer Vaccine by Early Next Month

The Food and Drug Administration’s move is expected to kick off more vaccination mandates for hospital workers, college students and federal troops.

Is the Delta Variant Making Younger Adults ‘Sicker, Quicker’?

Many doctors on the front lines say unvaccinated patients in their 20s and 30s are becoming more severely ill, and more quickly. But comprehensive data is lacking.

Americans Suffer Pandemic Whiplash as Leaders Struggle With Changing Virus

An evolving virus and 18 months of ever-changing pandemic messaging have left Americans angry, exhausted and skeptical of public health advice.

The Delta Variant in Schools: What to Know

Classrooms are opening their doors to a different pandemic. Here is how to think about risk.

‘It’s Nowhere Near Over’: A Beach Town’s Gust of Freedom, Then a U-turn

Provincetown, Mass., the quirky community at the tip of Cape Cod, thought it was safe to return to prepandemic partying. It wasn’t.

Who Are the Unvaccinated in America? There’s No One Answer.

One segment of people who have avoided shots is vehemently opposed to the idea. But there is a second group, surveys suggest, that is still deciding.

Vaccinated People May Spread the Virus, Though Rarely, C.D.C. Reports

The agency cited an outbreak in Provincetown, Mass., in which most of the infected were immunized. An internal C.D.C. document paints an even more harrowing picture.

C.D.C. Internal Report Calls Delta Variant as Contagious as Chickenpox

Infections in vaccinated Americans are rare, compared with those in unvaccinated people, the document said. But when they occur, vaccinated people may spread the virus just as easily.

Biden Seeks to Revive Vaccine Effort With New Rules and Incentives

The president said those refusing to get a coronavirus shot should expect inconveniences as long as they decline a vaccine.