(Reuters)

The United States can immediately resume use of Johnson & Johnson’s COVID-19 vaccine, top health regulators said today (April 23), ending a 10-day pause to investigate its link to extremely rare but potentially deadly blood clots.

The Centers for Disease Control and Prevention (CDC) and Food and Drug Administration said the risks of experiencing the syndrome involving severe blood clots and low platelets as a result of the vaccine was very low. They found 15 cases in the eight million shots given.

“We are no longer recommending a pause in the use of this vaccine,” CDC Director Rochelle Walensky told a news briefing. “Based on the in-depth analysis, there is likely an association but the risk is very low.”

DECISION EFFECTIVE IMMEDIATELY

Top US FDA officials said the decision was effective immediately, clearing the way for shots in arms as early as Saturday. The agency said it would warn of the risk in an updated fact sheet given to vaccine recipients and providers.

The agencies made the decision following a meeting of outside advisers to the CDC who recommended that the vaccine pause be ended.

In an analysis presented at the meeting, CDC staff said that the cases of the syndrome that they had found occurred at a rate of seven per one million doses in women under age 50, with the highest risk occurring among women ages 30 to 39.

For women over age 50 and for all men, the clots appeared at a rate of one per one million doses, the analysis showed. In all, there were three deaths, officials said.

After a day-long meeting, the CDC panel voted 10-4 that the J&J vaccine be used as recommended in people 18 years of age and older, the parameters of its current FDA authorisation.

Dr Jesse Goodman, an infectious disease expert at Georgetown University in Washington and a former chief scientist at the FDA, said the risk was not trivial, but still small.

“But we should keep it in perspective. I mean the risk of dying from a car accident in your life is something like one in 100, the risk of being struck by lightning is something like one in 15,000,” Goodman said.

Unlike the highly effective vaccines by Pfizer Inc and Moderna Inc, which require two doses and must be kept frozen at ultra-cold temperatures, J&J’s vaccine can be given in a single dose and stored at regular refrigeration temperatures, making it a better option for hard-to-reach areas.

Johnson & Johnson shares closed up 0.2 per cent at US$165.52.

EARLY IDENTIFICATION

“We will collaborate with health authorities around the world to educate healthcare professionals and the public to ensure this very rare event can be identified early and treated effectively,” J&J’s Chief Scientific Officer Paul Stoffels said in a statement after the agencies made their announcement.

When the agencies first announced the pause, they urged doctors to avoid using the blood thinner heparin, commonly given to patients to break up blood clots, in people who had received the J&J vaccine and were experiencing blood clots and low blood platelets.

In the cases of the vaccine-induced blood clots, however, heparin appears to make the condition worse. Walensky said doctors heeded that warning, noting that the drug had not been used in any of the cases identified after the pause began.

The US decision follows a similar one by the European Medicines Agency, which on Tuesday said the benefits of the J&J shot outweighed its risks and recommended adding a warning about unusual blood clots with low blood platelet counts to the vaccine’s product label. J&J resumed its rollout there.

The J&J probe followed an investigation in Europe of the AstraZeneca PLC vaccine, with which similar cases of blood clots were first identified. Dr Peter Marks of the FDA said the cases appear so similar that a doctor would not be able to tell which vaccine caused them.

Both the J&J and AstraZeneca vaccine use different versions of a cold virus to deliver instructions for making coronavirus proteins into cells to produce an immune response. Marks said studies are under way to determine whether the adenovirus or something else is behind the rare blood clots.

Dr William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, said the J&J vaccine will help advance the vaccination effort.

“Giving people the choice to receive a single-dose vaccine will help get more people vaccinated faster and will better protect some populations, such as those who are homeless or incarcerated,” Moss said by email.

J&J has faced several setbacks since its vaccine gained U.S. emergency authorisation in February, including drawing scrutiny over production shortfalls.

In the United States, 35 per cent of adults are fully vaccinated and 53 per cent have received at least one shot, according to CDC data. The United States leads the world with roughly 570,000 COVID-19 deaths.