Johnson & Johnson’s single-dose COVID-19 vaccine is cleared for use in the U.S.

Johnson & Johnson’s coronavirus vaccine was cleared for use in the U.S., making a third shot available that could plug gaps in the nation’s immunization campaign as concern grows over an influx of virus variants.

The Food and Drug Administration said in a statement today that it had granted an emergency-use authorization for the single-dose vaccine for people 18 and older.

The decision comes after the U.S. hit a sad milestone with 500,000 Americans dead from the virus, and at a time when health officials are raising alarms that recent declines in the number of new cases may be stalling.

The J&J shot is highly effective at preventing severe Covid-19, with no serious side effects, agency staff said in a report Wednesday. On Friday, a committee of outside advisers to the FDA voted unanimously that the vaccine’s benefits outweigh any risks. In the week ahead, J&J is prepared to ship 3 million to 4 million doses, Biden administration officials have said.

“We’re in a race between the virus mutating — new variants coming out that could cause further disease — and stopping it,” said Jay Portnoy, director of the division of allergy, asthma and immunology at Children’s Mercy Hospital, who supported an emergency authorization. “We need to get this vaccine out.”

The clearance marks another milestone in an unprecedented global scientific sprint. Since the World Health Organization declared the coronavirus a pandemic nearly a year ago, numerous vaccines have been deployed around the world, including shots developed in China and Russia. Worldwide, more than 231 million doses have been administered in 100 countries, according to data collected by Bloomberg.

J&J’s shot is expected to be easier to distribute and administer than the Pfizer Inc.-BioNTech SE vaccine and the Moderna Inc. shot that were cleared by the FDA late last year. To reach full effectiveness, the earlier shots require two doses several weeks apart. They must also must be kept at very cold temperatures, while J&J’s doses can be stored in a refrigerator for long periods.

Its simplicity could make J&J’s shot especially beneficial for hard-to-reach rural areas that have seen higher rates of virus cases and deaths.

The authorization comes as the inoculation drive in the U.S. has accelerated, with more than 70.5 million doses given as of Friday, according to Bloomberg’s Vaccine Tracker. At the same time, the rise of new coronavirus variants has increased the urgency to get more people vaccinated.

New fast-spreading mutations first reported in the U.K., South Africa and Brazil have appeared in the U.S., while domestic variants spotted in California and New York are raising new concerns among some scientists.

J&J is on track to supply 20 million doses to the U.S. by the end of March, and 100 million by the end of June, an executive said at a congressional hearing on Feb. 23. Globally, J&J expects to produce 1 billion doses this year. Regulators in the European Union could clear the shot in early March.

J&J’s shot is unlikely to be the last to come available in the U.S. Both Astrazeneca Plc and Novavax Inc. are expected to seek authorization in the coming months for their vaccines, pending results of big U.S. trials that are now fully enrolled.

DIFFERENT PLATFORMS

J&J’s vaccine is made from a common cold virus that doesn’t replicate in the body but triggers an immune response to fight off infection. In the U.S. portion of a more than 43,000-person global trial, it was found to be 72% effective at preventing moderate to severe Covid.

That is a lower overall efficacy rate than the Pfizer-BioNTech and Moderna vaccines, which are based on technology called messenger RNA that primes the body to ward off the virus. Each of those was found to be more than 90% effective.

Still, all three shots are extremely reliable at preventing hospitalizations and deaths. And J&J’s does that quickly, with protection against severe disease starting only seven days after vaccination, and ramping up over the course of about two months.

Public-health officials hope that as more people get them, they will greatly reduce the strain the pandemic has placed on the health-care system. Already, more people in the U.S. have received at least one vaccine dose than have tested positive for the virus.

VIRUS MUTATIONS

Policy makers are eager to get more people immunized before virus mutations can take firmer hold in the U.S.

J&J’s vaccine provided less protection against the new variants, trial data suggested. In Brazil, the shot was 68% effective against moderate-to-severe disease 28 days after vaccination, while in South Africa it was 64% effective. But across the globe, including in countries with emerging variants, the shot successfully prevented all hospitalizations and deaths.

Mathai Mammen, the head of global research and development for J&J’s pharmaceutical division, said in an interview last month that it’s impossible to compare overall efficacy levels between the vaccines, given that the trials were carried out in different locations at different times in the course of the pandemic.

“What people fear is getting sick, so sick they have to go to an emergency room, or hospital, and even die,” he said “This vaccine, in a single shot, protects completely from that kind of fear.”

J&J is still testing a two-shot regimen in a large, global trial that is expected to produce results before year-end. Like Pfizer and Moderna, the company is working on boosters tailored to the variants. And it plans studies soon in children, pregnant women and the immunocompromised.

J&J executives have said the company will charge no more than $10 a dose for the vaccine during the pandemic — a price at which it won’t profit. The Pfizer-BioNTech vaccine costs the U.S. $39 for the full regimen, and the Moderna vaccine costs $33 for both doses.

PANDEMIC PREPAREDNESS

New Brunswick, New Jersey-based J&J has spent more than a century combating infectious diseases. It created the so-called Epidemic Mask to prevent the spread of the 1918 Spanish Flu, and developed an Ebola vaccine that was approved in Europe in 2020.

Its Covid-19 vaccine uses the same adenovirus platform that is the basis of the Ebola shot. The company collaborated on its development with researchers from Harvard University and U.S. health agencies, including the Biomedical Advance Research and Development Authority and the National Institutes of Health.

Like the Pfizer-BioNTech and Moderna shots, J&J’s vaccine was one of six that was selected by the Trump administration’s Operation Warp Speed program, receiving some $1.5 billion in backing from the U.S. government, which has options to acquire additional supply.

J&J Chief Scientific Officer Paul Stoffels said he hopes it’s another hundred years before another pandemic sweeps the world, but realistically, the U.S. should have a heightened alert that it could happen at any time.

“A whole new field of science and pandemic preparedness is needed,” Stoffels said.