Experts call Johnson & Johnson's single-dose COVID vaccine 'very promising.' Here's what you need to know.

Rachel Grumman Bender
·6 min read

Johnson & Johnson’s single-dose COVID-19 vaccine candidate looks promising based on initial results from the ongoing trial published in the New England Journal of Medicine.

The phase 1-2a trial, which started in July 2020 in the U.S. and Belgium, includes a total of 805 study participants — healthy adults between 18 and 55 years old and those 65 and older — who were randomly assigned high or low doses of the COVID-19 vaccine candidate or a placebo.

Early data shows that after a single dose of the vaccine candidate, neutralizing antibodies against COVID-19 were found in 90 percent or more of study participants at day 29 of the trial, regardless of the vaccine dose given, and 100 percent of participants ages 18 to 55 years old by day 57, according to the study. A Johnson & Johnson press release on the study stated that the antibodies “remained stable through Day 71” — the length of time measured so far in the ongoing trial.

Data on how long the immune response lasts in trial participants over age 65 will be available in late January, according to the press release, which also noted that the researchers plan to do “longer-term follow-up to one year” as well. According to CNBC, “the company is expected to release results from its 45,000-person phase III trial later this month.”

An illustrative image of medical syringes in front of Johnson and Johnson logo displayed on a screen. On Friday, January 8, 2020, in Dublin, Ireland. (Photo by Artur Widak/NurPhoto via Getty Images)
Early data shows that after a single dose of the vaccine candidate, neutralizing antibodies against COVID-19 were found in 90 percent or more of study participants on day 29 of the trial, regardless of the vaccine dose given. (Photo by Artur Widak/NurPhoto via Getty Images)

The study found that the vaccine candidate was “generally well tolerated” in all study participants. The most common side effects included fatigue, headache, muscle ache and pain at the injection site, as well as fever.

Dr. Purvi Parikh, allergist and immunologist with the Allergy and Asthma Network, tells Yahoo Life that the vaccine candidate is “very promising if it proves effective” in the next phases of the trials. “So far from early data on 800 participants, it seems that 90 percent of the participants mounted immunity one month after the shot and all had it two months after. Now we need to see how reproducible this is in the larger phase III studies with 30,000 to 60,000 people. We also need to see how this prevents infection and spread.”

Dr. Philip Grant, infectious disease doctor and lead investigator of the Johnson & Johnson COVID-19 vaccine trial at Stanford University, tells Yahoo Life that the study results are “encouraging,” adding: “I’m optimistic.”

Grant says that the early trials show “a good immune reaction” from the vaccine without many side effects. “I think it’s encouraging that it’s well tolerated,” Grant says.

It’s not yet known how protective the Johnson & Johnson vaccine is against COVID-19 (both Pfizer and Moderna are about 95 percent effective). Grant explains that the phase III trial will show what the percentage of effectiveness will be.

How does the Johnson & Johnson COVID vaccine candidate work?

Johnson & Johnson’s vaccine candidate uses an adenovirus (a common virus that causes coldlike symptoms) that has been modified so it can’t replicate and make people sick. “The adenovirus carries a gene from the coronavirus into human cells, which then produce the coronavirus spike protein, but not the coronavirus itself,” according to a release from Johnson & Johnson. “This spike protein is what primes the immune system to fight off a subsequent infection by the virus.”

Adenoviruses have been used for years in other drugs — for example, Johnson & Johnson used it in its Ebola vaccine, stating in the release that there’s “a lot of long-term safety data for it.”

Pfizer’s and Moderna’s COVID vaccines, on the other hand, use mRNA technology, which gives “instructions for our cells to make a harmless piece of what is called the ‘spike protein,’” according to the Centers for Disease Control and Prevention, which is found on the surface of the virus that causes COVID-19. “Our immune systems recognize that the protein doesn’t belong there and begin building an immune response and making antibodies. ... At the end of the process, our bodies have learned how to protect against future infection.”

How else is the Johnson & Johnson COVID vaccine candidate different from Pfizer’s and Moderna’s vaccines?

Johnson & Johnson’s COVID-19 vaccine candidate requires only a single shot — what Grant calls a “huge” advantage over Pfizer’s and Moderna’s vaccines, which both require a second dose spaced 21 days and 28 days apart, respectively.

Another advantage: Johnson & Johnson’s COVID vaccine “can be stable for several months in just routine refrigerators,” says Grant. “So distribution will be similar to most other [non-COVID] vaccines.” Pfizer’s vaccine, however, needs to be shipped at extremely cold temperatures (-70°C) and can be stored for only five days at a refrigerated temperature of 2°C to 8°C. Moderna’s vaccine also needs to be stored in a freezer between -25°C and -15°C.

What would a third vaccine mean for vaccine rollouts in the U.S.?

Both Grant and Parikh agree that a third vaccine option would potentially help speed up vaccinations in the U.S. “It would definitely help reach herd immunity faster, as there would be more vaccine supply,” says Parikh, “and with only one dose we can get people vaccinated faster.”

More than 9 million Americans have been vaccinated just one month after the first COVID-19 vaccine was administered in the U.S. Grant says that if the goal is to get at least 150 million people vaccinated by summer, “you can see we’re way behind on that pace to get to that number. … Unless there’s another vaccine, it doesn’t seem like it’s going to happen.”

Grant adds: “Based on the current pace, it looks like we wouldn’t be out of the woods until October, if we’re being optimistic. I think this [third vaccine] would potentially get us to the point where, by summertime, we’re in a much better place than we are now.”

What happens next?

If Johnson & Johnson’s single-dose COVID vaccine candidate is shown to be safe and effective in its phase III trials, the company will submit an application for an Emergency Use Authorization (EUA) with the U.S. Food and Drug Administration, according to the press release. Grant estimates that the earliest the vaccine could get a EUA is in February, with the first person potentially getting the vaccine in late February or early March at the very earliest.

For the latest coronavirus news and updates, follow along at According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.

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