Research has shown that the biotech firm’s shot is effective at preventing people from getting sick with COVID-19, but there’s no hard evidence that it stops them from carrying the virus “transiently” and potentially infecting others who haven’t been vaccinated, according to Dr. Tal Zaks, Moderna’s chief medical officer.

improved efficacy and less vaccine.

The [rapid] test can detect more than 80 percent of infections found by the lab-based P.C.R. test. But when used to screen asymptomatic people, it detected only 32 percent of the positive cases identified by the P.C.R. test.

In April, as coronavirus cases multiplied across the country, the head of the U.S. Environmental Protection Agency rejected scientists’ advice to tighten air pollution standards for particulate matter, or soot.

In the next few weeks, EPA Administrator Andrew Wheeler likely will reaffirm that decision with a final ruling, despite emerging evidence that links particulate pollution to COVID-19 deaths.

There was enough evidence to support a stricter standard before the pandemic, said Christopher Frey, an environmental engineering professor at North Carolina State University who studies air pollution. The added threat from the coronavirus is like “icing on the cake,” he said, and should compel Wheeler to adopt an even more stringent limit.

Particulate matter kills people. “It is responsible for more deaths and sickness than any other air pollutant in the world,” said Gretchen Goldman, a research director at the Union of Concerned Scientists.