Johnson & Johnson’s (J&J) single dose vaccine is seen as an important tool in the fight against a pandemic that has claimed more than three million lives.
An advisory committee to the U.S. Centers for Disease Control and Prevention (CDC) will hold a meeting on Wednesday to review the cases linked to the J&J vaccine, and the U.S. Food and Drug Administration (FDA) will review the analysis, the agencies said in a joint statement.
All six recipients were women between the ages of 18 and 48, and the symptoms occurred six to 13 days after vaccination.
The CDC and FDA said the adverse events appeared to be extremely rare.
J&J said it was working closely with regulators and noted no clear causal relationship had been established between the events and the COVID-19 vaccine made by its Janssen unit.
As of April 12, more than 6.8 million doses of the J&J vaccine had been administered in the United States.
European officials have said J&J began delivering its COVID-19 vaccine to EU countries on Monday and had committed to delivering 55 million doses to the bloc by the end of June and another 120 million in the third quarter.
Europe’s drugs regulator continues to recommend the use of AstraZeneca’s COVID-19 vaccine, saying the benefits outweigh the risks. Several EU countries, however, have limited its use to certain age groups.