As of Tuesday, 7.2 million people in the United States had received the vaccine without any other serious adverse reactions reported.
Experts have yet to determine to what extent, if any, the vaccine is responsible for the clots. But the investigation follows actions by European regulators who concluded that a vaccine made by AstraZeneca may also be the cause of a similar, extremely rare clotting disorder.
U.S. and European public health experts have emphasized that for most people, the benefits of the Covid vaccines far outweigh the risks.
Several countries in Europe last week restricted use of the AstraZeneca-Oxford vaccine to older adults because rare cases of a blood disorder were occurring in younger people. The AstraZeneca vaccine has not been authorized in the United States.
Fewer than one in a million J&J vaccinations are now under investigation. If there is indeed a risk of blood clots from the vaccine — which has yet to be determined — that risk is extremely low. The risk of getting Covid-19 in the United States is far higher.
People should not be concerned about mild headaches and flu-like symptoms in the first few days after vaccination. Those are common, harmless side effects brought on by the immune system’s production of a defense against the coronavirus.
For people who received the vaccine a month or two ago, the issue being raised about clots “doesn’t mean anything,” Dr. Fauci said. The six cases occurred within a “pretty tight window” of six to 13 days after people received the shot, he said.