CDC’s Advisory Committee on Immunization Practices (ACIP) voted 15 to 0 to prioritize the Pfizer-BioNTech and Moderna COVID-19 vaccines over Johnson & Johnson’s.

One of the main reasons for the recommendation is a rare side effect associated with the Johnson & Johnson vaccine that results in low blood clots and blood-platelet levels.

CDC officials revealed that there had been 54 cases of the condition, known as thrombosis with thrombocytopenia syndrome.

FDA temporarily paused the use of the vaccine in April over blood clot concerns.

The J&J vaccine has lagged behind the mRNA-based Pfizer-BioNTech and Moderna vaccines in terms of demand.

To date, U.S. health workers have administered 17 million doses of the Johnson & Johnson vaccine compared to 286 million Pfizer-BioNTech doses and 187 million Moderna doses, according to CDC data.

The J&J vaccine also trails its rivals in terms of vaccine efficacy.

That said, it has found use in certain settings such as among homeless and prison populations.