WASHINGTON — The Biden administration said Friday that it did not know that a Baltimore factory had discarded millions of possibly contaminated doses of AstraZeneca’s coronavirus vaccine when President Biden last month released the company to ship vaccines manufactured there to Mexico and Canada.

Canadian and Mexican officials said on Friday that they had assurances from AstraZeneca that the millions of doses they received were safe. Some of the doses have been distributed to the public in both countries, the officials said.

TOKYO — Japan on Friday declared states of emergency in Tokyo, Osaka and surrounding areas in an effort to stem a widening coronavirus outbreak three months before the country plans to host the Summer Olympics.

The measures will take effect on Sunday, Prime Minister Yoshihide Suga said, calling them “a short and concentrated measure” to slow the virus’s spread during the Golden Week holiday, traditionally one of the year’s busiest travel periods.

The health effects of Covid-19 not only can stretch for months but appear to increase the risk of death and chronic medical conditions, even in people who were never sick enough to be hospitalized, a large new study finds.

In the study, published Thursday in the journal Nature, researchers looked at medical records of more than 73,000 people across the United States whose coronavirus infections did not require hospitalization. Between one and six months after becoming infected, those patients had a significantly greater risk of death — 60 percent higher — than people who had not been infected with the virus.