How does the Johnson & Johnson vaccine work? When is it available? What to know about the new shot.

By | March 1, 2021

“You now have three highly efficacious vaccines, for sure, there’s no doubt about that,” Anthony S. Fauci, the nation’s top infectious-disease expert, said the day after the Food and Drug Administration authorized the Johnson & Johnson vaccine. “I think people need to get vaccinated as quickly and as expeditiously as possible.”

With the rollout starting soon, here’s what you need to know.

How is this vaccine different from the first two?

The first two vaccines approved for use in the United States — one made by Pfizer and BioNTech, the other by Moderna — require two shots, given weeks apart. The first dose offers partial protection and the second acts as a booster. The two-step system has prompted debate and complicated the vaccination effort.

Unlike traditional vaccines, those made by Pfizer and Moderna use messenger RNA technology to train the immune system to respond to the coronavirus.

Both the Pfizer and Moderna doses must be kept ultracold or frozen, a requirement that has presented challenges during power outages or technology failures when health workers have had to scramble to administer shots or risk the vaccine supply going to waste.

All in all, the Johnson & Johnson vaccine is less fussy.

For starters, it’s a one-stop shot. No waiting weeks for another appointment. No logistical headaches from keeping track of who needs their second dose and who’s still waiting on their first.

The Johnson & Johnson vaccine does not use mRNA. Rather, it’s what’s known as an adenovirus vector vaccine. It uses the more established approach of employing a harmless cold virus to deliver a gene that carries the blueprint for the spiky protein found on the surface of the coronavirus. The virus enters cells, which then follow the genetic instructions to construct a replica of the coronavirus spike. The immune system uses these replicas to recognize — and respond to — the real thing.

The coronavirus vaccine produced by the University of Oxford and AstraZeneca is also based on adenoviruses, as is a Johnson & Johnson-made vaccine for Ebola, which was approved by the European Medicines Agency last year.

The Johnson & Johnson vaccine “doesn’t give you covid, because it’s not the virus,” Fauci said in a recent public service announcement. “It’s just one protein from the virus that induces your body to make a good response against the whole virus.”

Finally, the shots can be stored for months at refrigerator temperature.

How effective is the Johnson vaccine?

The bottom line: All three vaccines are “highly efficacious and quite safe,” said Philip J. Landrigan, an epidemiologist and the director of Boston College’s Program for Global Public Health and the Common Good.

The Johnson & Johnson vaccine completely prevented hospitalization and death, including in South Africa against a more transmissible variant, and was 85 percent effective at protecting against severe cases of illness.

It was 72 percent effective at preventing moderate illness in the U.S. trials, a number that falls short of the Pfizer and Moderna vaccines, which were about 95 percent effective after both doses. However, experts say head-to-head comparisons among the vaccines cannot be made, because the trials were conducted at different times during the pandemic and in different countries dealing with different variants and transmission rates.

Scientists also note that the newest vaccine’s efficacy is far higher than the FDA’s 50 percent requirement.

Advisers to the Centers for Disease Control and Prevention strongly endorsed the vaccine’s effectiveness after its approval.

“Anything that keeps people from getting sick and anything that keeps people from going to the hospital and anything that keeps people from dying is a good thing,” Landrigan said.

When will it be available?

In some places, imminently.

The move from the FDA authorizes the vaccine for emergency use in people ages 18 and older, and the doses were set to ship out on Monday, within 48 hours of approval. They will go first to sites already receiving doses of the two other vaccines, including state health departments, pharmacies, federally qualified health centers and community vaccination centers.

Initial supplies of the vaccine will be limited, with about 4 million doses expected to ship during the first week of distribution. However, production will ramp up in the weeks that follow, and the company says 20 million doses will be delivered by the end of March and 100 million by the end of June.

Can I get more than one vaccine?

Current CDC guidance states that the Pfizer and Moderna vaccines “are not interchangeable with each other or with other covid-19 vaccine products.” So, the answer is: No, you shouldn’t get more than one type of coronavirus vaccine, and you shouldn’t mix the two-dose vaccines.

The CDC affixes its advice with the following disclaimer: “Recommendations may be updated when further information becomes available.” Scientists are probably still studying this question, and Landrigan said people should stick to what has been tested and approved.

“There’s always a possibility that there could be a cross-reaction between the two,” he said. “Nobody has data on that, but it’s a possibility.”

Can I choose which vaccine to get?

Across the board, vaccine supply is still scarce. Public health experts agree that, as the sports maxim goes, the best ability is availability.

It’s natural to compare medicines, Landrigan said, but at this point in the pandemic, being too choosy could be costly.

“People comparison shop all the time for everything,” he said. “But my advice to people is to get whatever vaccine first becomes available in your community. Don’t delay, because every day you delay is a day you’re unprotected.”

What does this mean for the pandemic?

This is good news. Very good news.

The demand for shots currently outstrips the supply, and another approved vaccine means more people will be able to get inoculated faster.

“It will help to finally quell this terrible pandemic,” Landrigan said.

It comes at an important time. When the Johnson & Johnson vaccine was approved, the downward trend in new coronavirus infections had plateaued, perhaps because officials relaxed public health restrictions too soon and more contagious virus variants were becoming more widespread. Experts say a vigorous vaccination effort is key to stamping them out.

At the pandemic’s outset, few would have predicted that Americans would have access to three vaccines within a year.

“It’s extraordinary. I’ve never seen anything like it,” said Landrigan, who spent 15 years at the CDC. “I don’t think any of us expected we would have one, let alone three vaccines, in a matter of 12 months. It’s unprecedented.”

He added: “So long as the virus doesn’t evade us, I think we’re on the right track.”

Lena H. Sun, Carolyn Y. Johnson and Laurie McGinley contributed to this report.

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