By Thomas M. Burton and Eric Sylvers 

Europe's health agency said a warning should be added to the product information of the Johnson & Johnson Covid-19 vaccine that unusual blood clots are a very rare possible side effect, but that the benefits of taking the shot outweigh the risks.

In the U.S., the number of cases of blood-clot disorders linked to the vaccine has increased to nine, up from the six initially reported, according to a senior U.S. health official. The European Medicines Agency said Tuesday that it had looked at data from the U.S.

The nine U.S. cases are being investigated, the official said. Use of the J&J vaccine has been temporarily suspended on the recommendation of the Food and Drug Administration and Centers for Disease Control and Prevention.

The instances of clots overall is still very small given that about seven million doses of the vaccine have been administered in the U.S.

Last week, U.S. health authorities recommended pausing the rollout out of the J&J vaccine. They had considered only issuing a warning, but decided a pause would help make doctors aware of how to treat the rare condition. J&J then followed with the decision to pre-emptively pause the rollout in Europe, which had just begun.

An advisory committee to the CDC is scheduled to meet Friday to advise the U.S. about the next course of action. Federal authorities have been considering a possible age restriction -- the U.S. cases were all in people 48 years old or younger -- or adding cautionary language to doctors who use the vaccine.

The cases in the U.S. were similar to those that have occurred with the AstraZeneca PLC vaccine in Europe, something that the EMA said it took into consideration in making its recommendation. The two vaccines use similar technology.

In the U.K., where 20.6 million people had received at least one dose of the AstraZeneca vaccine by April 5, there has been about one case of the unusual clotting with low platelets for every 200,000 shots given. There have been 22 deaths out of 99 cases. The majority of cases and deaths have been in women under 60 years old, prompting many countries to restrict the use of the vaccine to older recipients.

The U.S. official noted that more cases could still arise. The cases so far involved blood clots in a major vein draining the brain, while the patients had sharp drops in their blood platelets and, in some cases, bleeding.

Because some of the patients got the wrong treatment -- the blood-thinner heparin -- U.S. authorities issued a pause on the use of the J&J vaccine.

The AstraZeneca vaccine, a similar type to the J&J one, is known as an adenovirus-vector vaccine, in which a virus causing the common cold is altered to cause human cells to grow spikes similar to those of the spike protein on coronavirus cells.

The changes in a vaccine recipient's cells cause an immune response to the coronavirus cells that protects a large percentage of recipients against the virus.

The AstraZeneca vaccine hasn't yet been authorized for use in the U.S.

Write to Thomas M. Burton at tom.burton@wsj.com and Eric Sylvers at eric.sylvers@wsj.com

 

(END) Dow Jones Newswires

April 20, 2021 12:46 ET (16:46 GMT)

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