US health authorities are calling for a pause in the use of the Johnson & Johnson Covid-19 vaccine, after reports of extremely rare blood clotting cases.
The Food and Drug Administration (FDA) said six cases in 6.8 million doses had been reported and it was acting “out of an abundance of caution”.
Johnson & Johnson said it was also delaying its vaccine rollout in Europe.
The US move follows similar rare cases in the AstraZeneca vaccine, which has prompted some curbs in its use.
The US has by far the most confirmed cases of Covid-19 – more than 31 million – with more than 562,000 deaths, another world high.
The picture for the virus in the US is complicated, though, with some areas in the north seeing surges in infections, the south less, and with the figures not always reflecting inoculation numbers.
The Johnson & Johnson jab was approved in the US on 27 February and its use has been more limited so far than that of the Pfizer-BioNTech and Moderna doses.
Nevertheless, the government had hoped for hundreds of thousands of vaccinations of the jab every week as it is single-shot and its storage at common refrigerator temperatures makes it easier to distribute.
It is also known as the Janssen vaccine, named after the Belgian company that makes it.
South Africa became the first country in the world to administer the jab, and nearly 300,000 health workers have received it since mid-February. Health authorities there have not yet decided whether the roll out will continue.
The vaccine is yet to be approved in the UK, although 30 million doses are on pre-order. The Department of Health said the rollout delay would not affect vaccine supplies in the UK, or derail the aim to offer a jab to all adults by the end of July.