U.S. health authorities said Friday that the use of Johnson & Johnson's coronavirus vaccine can be resumed immediately, emphasizing its safety after a few blood clot cases led them to recommend a pause on April 13.

Following a thorough safety review, the U.S. Food and Drug Administration and the Centers for Disease Control and Prevention said in a press release that they have "confidence that this vaccine is safe and effective in preventing COVID-19."

Photo illustration shows a silhouette of a man holding a medical syringe and a vial seen displayed in front of the Johnson and Johnson logo on a screen. (SOPA Images/LightRocket/Getty/Kyodo

The pause was recommended following reports of six cases of a rare and severe type of blood clot in individuals who had received the shot. At that time more than 6.8 million doses of the J&J vaccine had been administered in the United States.

The authorities said they eventually confirmed a total of 15 cases, including the six originally confirmed cases, among women between the ages of 18 and 59.

Symptoms occurred six to 15 days after vaccination. Three died, seven remain hospitalized and five have been discharged, according to the CDC.

"Based on the in-depth analysis, there is likely an association, but the risk is very low," CDC Director Rochelle Walensky told a press conference as she explained the reason for lifting the recommended pause.

In late February, the FDA granted the J&J one-shot vaccine emergency use authorization for individuals 18 years of age and older. It was the third COVID-19 vaccine approved in the United States, after one developed by U.S. pharmaceutical giant Pfizer Inc. and its German partner BioNTech SE, and another by U.S. company Moderna Inc.