US regulators recommended resuming vaccinations with the Johnson & Johnson coronavirus vaccine on Friday, determining the single dose jab is "safe and effective".
The vaccine has been paused in the country since 13 April after reports of six women developing rare but serious blood clots following vaccination.
The US Food and Drug Administration (FDA) and Centres for Disease Control and Prevention (CDC) determined that the vaccine's "known and potential benefits outweigh its known and potential risks" in people over the age of 18.
"Above all else, health and safety are at the forefront of our decisions," said CDC director Rochelle Walensky in a statement.
"Our vaccine safety systems are working. We identified exceptionally rare events – out of millions of doses of the Janssen (J&J) COVID-19 (vaccine) administered – and we paused to examine them more carefully."
Countries in Europe have also begun rolling out the J&J vaccine, which will likely help to speed along vaccination campaigns as it only requires a single dose.
The European Medicines Agency (EMA) had determined that there was a "possible link" between the vaccine and rare blood clots but determined that the benefits of vaccination outweigh the risks.
"We appreciate the rigorous review of the PRAC [EU regulator's safety committee] and share the goal of raising awareness of the signs and symptoms of this very rare event to ensure the correct diagnosis and appropriate treatment,” said Paul Stoffels, Johnson & Johnson's chief scientific officer after the EMA review.
The J&J vaccine had been conditionally authorised for use in the European Union on March 11.
It was shown to be 67 per cent effective in clinical trials as there were just 116 COVID-19 cases out of 19,630 people who received the vaccine. In a similar-sized group of people who received the placebo, there were 348 COVID-19 cases.
The Johnson & Johnson vaccine uses an adenovirus vector, similar to the AstraZeneca vaccine, which has also been possibly linked to rare blood clots.
The EU regulator has said that one possible explanation for the rare blood clots is an immune response to the vaccine.
They warned people who have been vaccinated to seek medical attention if they experience symptoms such as shortness of breath, chest pain, leg swelling, abdominal pain, headaches, blurred vision or tiny blood spots under the skin.