Maria Cheng, Associated Press

Cases are confirmed among children and adults in more than a dozen countries, with few vaccine doses available on the continent.

In people with sickle cell — which is particularly common in people with African or Caribbean backgrounds — a genetic mutation causes the cells to become crescent-shaped, which can block blood flow and cause excruciating pain, organ damage, stroke and other problems.

Activists, doctors, politicians and at least five class-action lawsuits allege the practice has not ended in Canada.

The agency said a warning about the blood clots should be added to labels for the Johnson & Johnson’s vaccine and that these rare blood disorders should be considered “very rare side effects of the vaccine.”

The agency declined to impose any new age restrictions. Its U.K. counterpart, however, said it would offer people under 30 the choice of another product.

AstraZeneca said its experts did not identify any safety concerns related to the vaccine, including finding no increased risk of rare blood clots identified in Europe.

The agency said it “cannot rule out definitively a link” between rare types of blood clots and the vaccine, however, and experts recommend raising awareness among doctors and recipients of possible risks.

The decision should allow the U.N. agency’s partners to ship millions of doses to countries worldwide as part of a U.N.-backed program to tame the pandemic.

Scientists at Oxford University say their experimental coronavirus vaccine has been shown in an early trial to prompt a protective immune response in hundreds of people who got the shot.

The ship seemed to serve as an incubator for the new virus from China instead of an isolation facility meant to prevent the worsening of an outbreak.

An experimental Ebola vaccine tested on thousands of people in Guinea seems to work and might help shut down the waning epidemic in West Africa, according to interim results from a study published Friday.

At a public tasting in London Monday, Dutch scientists served hamburgers made from cow stem cells. Some questions and answers about the science behind the revolutionary patty.