With the FDA’s granting of emergency use authorization (EUA) to Johnson & Johnson (J&J), there is now a third vaccine – and the first requiring only a single shot – against COVID-19 for adult Americans.

Though it packs less of an efficacy punch, the EUA allows J&J’s Ad26.COV2.S to join mRNA vaccines from Moderna Inc. and Pfizer Inc./Biontech SE as protection against the virus.

New York-based Pfizer and Biontech, of Mainz, Germany, gained EUA status for BNT-162b2 and Cambridge, Mass.-based Moderna has the same for mRNA-1273, both of which showed 95% efficacy.

The J&J vaccine, which the company said it would begin shipping immediately, has a range of effectiveness. The EUA is based on data that include an analysis of 39,321 participants in an ongoing randomized, placebo-controlled study in South Africa, South America, Mexico and the U.S. in which 19,630 people received the vaccine and 19,691 received saline placebo. There was about 67% efficacy in preventing moderate to severe/critical COVID-19 at least 14 days after administration and 66% efficacy in preventing moderate to severe/critical COVID-19 at least 28 days after administration.

McKesson Corp. began distributing the vaccine on March 1. The U.S. government selected the company in August as a centralized distributor for frozen and refrigerated COVID-19 vaccines. In December, it began distributing Moderna’s vaccine but is not distributing Pfizer’s ultra-frozen vaccine.

On Jan. 29, J&J reported data from its global phase III Ensemble study showing an 85% efficacy rate, according to an interim analysis. The study met all its primary and key secondary endpoints. The vaccine also showed complete protection against COVID-19-related hospitalizations and death 28 days after vaccination.

J&J’s Ensemble study included data from an emerging viral variant most prevalent in South Africa. While the vaccine was 66% effective 28 days after patients were vaccinated, the onset of protection began on day 14. In the U.S. patient group, protection was 72%, while Latin American patients had 66% protection and patients in South Africa had 57% protection 28 days after vaccination, according to the interim analysis.

The J&J vaccine, an adenovirus serotype 26 vector encoding a full-length and stabilized SARS-CoV-2 spike protein, begins shipping immediately, with plans to deliver more than 20 million doses in March and more than 100 million doses in the first half of 2021. The company has repeatedly said it is committed to making the COVID-19 vaccine available on a not-for-profit basis for emergency pandemic use.

The FDA’s Feb. 27 EUA approval swiftly followed the previous day’s Vaccines and Related Biological Products Advisory Committee meeting, which looked favorably upon the J&J’s COVID-19 entry. Much discussion hinged on one question: “Based on the totality of scientific evidence available, do the benefits of [Ad26.COV2.S] outweigh its risks for use in individuals 18 years of age and older?” The result was unanimously yes, with 22 ballots.

Jay Portnoy, acting consumer rep and a professor of pediatrics at the University of Missouri Kansas City School of Medicine noted an urgency to move forward.

“We’re in a race [with] the virus mutating, new variants coming out that can cause further disease,” he said.

The FDA noted that, at this time, data are not available to determine how long the vaccine will provide protection, nor is there evidence that the vaccine prevents transmission of SARS-CoV-2 from person to person.

The Ensemble trial was stopped in October following a serious adverse event but resumed when it could not be determined that the event was caused by the vaccine. The EMA has initiated a rolling review.

J&J recently submitted an application to the EMA and filed for an emergency use listing with the World Health Organization.

The vaccine was developed by the Janssen Pharmaceutical Cos. of Johnson & Johnson. The company said it plans to file for a BLA in 2021.