Everything You Need to Know About Johnson & Johnson's COVID-19 Vaccine

On February 26, the FDA's vaccine advisory committee unanimously voted to recommend Johnson & Johnson's COVID-19 vaccine for emergency use. That means the vaccine — which requires only one dose — could be ready for use in the U.S. by the end of March, according to the Center for Infectious Disease Research and Policy (CIDRAP).

But, how effective is Johnson & Johnson's COVID-19 vaccine? And how does it compare to the other COVID-19 vaccines from Pfizer and Moderna? Here's what you need to know.

How does the Johnson & Johnson COVID-19 vaccine work?

If you're familiar with the COVID-19 vaccines created by Pfizer and Moderna, then you probably know they're both mRNA vaccines. That means they work by encoding a part of the SARS-CoV-2 virus's spike protein (the part of the virus that attaches itself to cells in your body) and using those encoded pieces to trigger an immune response from your body so that it creates antibodies against the virus. (See: How Effective Is the COVID-19 Vaccine?)

The Johnson & Johnson vaccine works a little differently. For one thing, it's not an mRNA vaccine. It's an adenovector vaccine, which means it uses an inactivated virus (in this case, adenovirus, which causes the common cold) as a vector to deliver proteins (in this case, the spike protein from SARS-CoV-2) that your body will recognize as a threat and create antibodies against, says Brittany Busse, M.D., associate medical director at WorkCare.

Now, you might be wondering if putting an "inactivated virus" in your body will inadvertently make you sick, but it won't. "An inactivated virus cannot replicate or cause you to be sick," says Abisola Olulade, M.D., a board-certified family medicine physician at Sharp Rees-Stealy Medical Group. Rather, the adenovirus in Johnson & Johnson's COVID-19 vaccine simply serves as the carrier (or "vector") of SARS-CoV-2's spike protein gene into your cells, causing the cells to make copies of that gene, she explains. Think of the spike protein gene as a set of instructions for how your body can fight off SARS-CoV-2, adds Dr. Olulade. "These spike proteins can be recognized by your immune system and cause you to generate antibodies that will protect against COVID," she explains. (FYI: The flu shot works in a similar way.)

While this vaccine technology is different from that of Pfizer and Moderna, it's not a novel concept. Oxford and AstraZeneca's COVID vaccine — which was approved for use in the EU and the UK in January (the FDA is currently waiting on data from AstraZeneca's clinical trial before considering U.S. authorization, the New York Times reports) — uses similar adenovirus technology. Johnson & Johnson has also used the technology to create its Ebola vaccine, which has been shown to be both safe and effective in producing an immune response in the body.

How effective is the Johnson & Johnson COVID-19 vaccine?

In a large-scale clinical trial of nearly 44,000 people, Johnson & Johnson's COVID-19 vaccine was shown to be 66 percent effective overall in preventing moderate (defined as having one or more COVID-19 symptoms) to severe COVID-19 (characterized by admission to an ICU, respiratory failure, or organ failure, among other factors) 28 days after vaccination, according to a press release from the company. (The data "will be submitted to a peer-reviewed journal in the coming weeks," states the press release.)

Johnson & Johnson also shared that its vaccine's level of protection against moderate to severe COVID was 72 percent in the U.S., 66 percent in Latin America, and 57 percent in South Africa (which, averaged together, gives you the overall 66 percent efficacy rate). If those numbers seem a bit underwhelming, it's worth noting that, by comparison, the flu shot is only 40 to 60 percent effective in protecting the body from influenza, yet it still plays a major role in reducing flu-related hospitalizations and deaths, says Dr. Olulade. (

Severe COVID-19 Illness and Death Data

At first, Johnson & Johnson's vaccine efficacy rate of 66 percent might seem somewhat low, especially when you compare it to the efficacy rates from Moderna (94.5 percent effective) and Pfizer ("more than 90 percent effective," according to the company). But if you dig deeper, Johnson & Johnson's data do show more promising results, particularly when it comes to the most severe COVID-19 cases.

Across all regions, the vaccine was 85 percent effective in preventing severe COVID-19, according to Johnson & Johnson's press release. In fact, the company noted that its vaccine showed "complete protection against COVID-related hospitalization and death" 28 days after vaccination, "with no reported cases" of COVID-related hospitalization or death among those who'd received Johnson & Johnson's vaccine.

In terms of side effects, Johnson & Johnson said its COVID vaccine was "generally well-tolerated" across all participants in the trial. The company's early data suggest that the vaccine may cause "mild-to-moderate side effects typically associated with vaccinations," including fatigue, headache, muscle soreness, and injection site pain.

COVID-19 Variants

Unlike Pfizer's and Moderna's studies, Johnson & Johnson's vaccine trial includes results across multiple regions — including those that have recently seen an uptick in COVID cases caused by emerging variants of the virus. "[These variants] may not have been dominant at the time when the previous vaccines were being studied," notes Dr. Olulade. Of course, researchers are now looking into how effective all COVID-19 vaccines might be in protecting the body from different COVID-19 variants. For now, Dr. Busse says the UK variant is "unlikely to be a concern for COVID vaccines." However, she adds, there is speculation that the COVID variants from South Africa and Brazil may "change the way antibodies interact with the virus" and potentially make those protective antibodies "less effective." (

That said, while the vaccine might not prevent COVID-19 infection altogether, it does seem to help people avoid the worst of the virus. "That also means that it has the potential to reduce the load on our overburdened health-care system and gets us closer to that light at the end of the tunnel," says Dr. Olulade.

"It's also important to remember that the sooner we can get people immunized, the fewer changes the virus has to mutate and replicate," adds Dr. Olulade. "That's why we need to get everyone [vaccinated] as soon as possible."

How many doses of the Johnson & Johnson COVID-19 vaccine do you need?

Aside from the efficacy of the vaccine itself, experts say Johnson & Johnson's COVID vaccine is also promising because it only requires a single shot, whereas Pfizer's and Moderna's vaccines each require two shots separated by a couple of weeks.

"This could really be a game-changer," says Dr. Olulade. "We do see that some patients, unfortunately, don't come back for their second dose," so this one-and-done approach could translate to more vaccinations overall.

Another major perk to Johnson & Johnson's COVID vaccine? The doses are apparently way easier to store and distribute than Pfizer's and Moderna's vaccines, thanks to J&J's use of adenovector vaccine technology. "Adenovirus [in Johnson & Johnson's vaccine] is cheaper and not as fragile [as the mRNA in Pfizer's and Moderna's vaccines]," the latter of which require storage at extremely cold temperatures, explains Dr. Busse. "The Johnson & Johnson vaccine is stable in the refrigerator for up to three months, which makes it easier to ship and distribute to those who need it."

How does Johnson & Johnson’s vaccine affect COVID-19 transmission?

"It's just too early to tell," says Prabhjot Singh, M.D., Ph.D., chief medical and scientific advisor of CV19 CheckUp, an online tool that helps evaluate your COVID-19 risks. That goes for all of the COVID-19 vaccines we've seen thus far BTW, not just Johnson & Johnson, notes Dr. Singh. "Early studies suggest that risk of transmission should decrease after being vaccinated, but a definitive answer requires a formal study," he explains.

Since the vaccines' effects on COVID transmission are still unknown, it's that much more important to continue wearing masks and maintaining your distance from people outside your home, says Dr. Olulade. (Wait, should you be double-masking to protect against COVID-19?)

Bottom line: All of these vaccines seem to offer significant protection against COVID-19, which is great. Still, "a vaccine is not a license to let down your guard," explains Dr. Olulade. "We have to unselfishly think about the health and wellbeing of others who have not yet been vaccinated and may not yet have protection from COVID."

The information in this story is accurate as of press time. As updates about coronavirus COVID-19 continue to evolve, it's possible that some information and recommendations in this story have changed since initial publication. We encourage you to check in regularly with resources such as the CDC, the WHO, and your local public health department for the most up-to-date data and recommendations.