Experts at the agency that regulates drugs for the European Union say they have found a "possible link" between the Johnson & Johnson COVID-19 vaccine and very rare blood clots after a small number of cases were reported in the US.
They confirmed the vaccine's benefits still outweighed the very small risks of recipients developing the unusual clots.
The European Medicines Agency said a warning about the rare blood clots should be added to labels for Johnson & Johnson's COVID-19 vaccine.
The agency said these rare blood disorders should be considered as "very rare side effects of the vaccine".
Last week, Johnson & Johnson halted its European roll-out of the vaccine after US officials recommended a pause in the vaccine when they detected six very rare blood clot cases among nearly 7 million people who had been vaccinated.
European officials said they considered all currently available evidence from the US, which consisted of eight reports of serious cases of rare blood clots associated with low blood platelets, including one death.
Last week, J&J halted its European rollout of its one-dose vaccine after the US Food and Drug Administration recommended officials pause its use while the rare blood clot cases are examined.
Officials identified six cases of the highly unusual blood clots among nearly 7 million people who were immunised with the shot in the U.S.
Johnson & Johnson advised European governments to store their doses until the EU drug regulator issued guidance on their use; widespread use of the shot in Europe has not yet started.
The delay was a further blow to vaccination efforts in the European Union, which have been plagued by supply shortages, logistical problems and concerns over unusual blood clots also in a small number of people who received the AstraZeneca COVID-19 vaccine.
Experts worry the temporary halt on J&J's shot could further shake vaccine confidence and complicate worldwide COVID-19 immunisation efforts.