FDA scientists did not reach a definitive conclusion in an online review. They cited shortcomings in J&J’s data and little information about protection against the extra-contagious coronavirus delta variant.

This review will take place ahead of Friday’s meeting when an FDA advisory panel will decide whether to approve booster doses of the J&J or Moderna vaccines. This is just one step in the government’s vaccine review process. Next week, FDA will make a final determination on authorizing these boosters and then the Centers for Disease Control and Prevention (CDC) will debate who should receive them.

According to health authorities, all vaccines in the U.S. provide strong protection against COVID-19-related death or severe illness. However, there are signs that milder infections protection may be diminishing. The government has already approved booster doses for some people who have had their last shot at Pfizer. This is six months after the last shot.

Moderna asked the FDA for uniform recommendations and requested that its booster dose be cleared at six months. J&J argued that the FDA should clear the booster dose at six months.

FDA reviewers stated that the FDA had reviewed the booster plan for two months and found “possible benefits.” However, they did not find any evidence of a large number of people who were able to get another shot at six-months.

The FDA’s reviewers concluded that the J&J vaccine “still affords severe COVID-19 death and disease protection.” However, data on its effectiveness are “consistently less” than those from Moderna and Pfizer shots.

J&J submitted data to the FDA from a real-world experiment that showed its vaccine is still about 80% effective against hospitalizations in America.

J&J’s single dose vaccine was highly anticipated due to its unique formulation. Its rollout was hampered by manufacturing issues and side effects, including a blood disorder and neurological reaction called Guillain Barre syndrome. Both cases were decided by regulators that the benefits outweighed the risks.

Moderna and Pfizer, rival drugmakers, have supplied the vast majority U.S. COVID-19 vaccinations. These two-dose shots have been used to fully immunize more than 170 million Americans, while the J&J shot has been used by less than 15million Americans.