Johnson & Johnson vaccine
Johnson & Johnson vaccineReuters

An advisory panel to the US Centers for Disease Control and Prevention (CDC) on Thursday unanimously voted to give a preferential recommendation to mRNA vaccines, like those made by Pfizer and Moderna, over the one-shot Johnson & Johnson vaccine due to rare but serious blood clots, Fox Business reports.

Rochelle Walensky, director of the Centers for Disease Control and Prevention, endorsed the policy several hours after the vote.

“Today’s updated recommendation emphasizes CDC’s commitment to provide real-time scientific information to the American public,” Walensky said in a statement.

The CDC temporarily halted Johnson & Johnson’s vaccine in April while scientists investigated the blood clots, which are known as "thrombosis with thrombocytopenia syndrome."

Regulators eventually decided that the benefits of the Johnson & Johnson vaccine outweigh the risks, but the FDA released new data this week showing that more cases have occurred in the summer and fall.

Only about 16 million doses of the Johnson & Johnson vaccine have been administered in the United States, compared to about 470 million doses of Pfizer and Moderna's vaccines.

The FDA cleared the Johnson & Johnson COVID-19 vaccine, which works with just one dose instead of two, in late February, but in addition to the blood clots, the vaccine has been plagued by problems, including stumbles at its US manufacturing plant.

In July, the FDA announced a new warning for the Johnson & Johnson coronavirus vaccine, saying the shot has been linked to a serious but rare side effect called Guillain-Barré syndrome, in which the immune system attacks the nerves.