Why the Johnson & Johnson Vaccine Should Reduce COVID-19 Transmission

Not only is the Janssen/Johnson & Johnson COVID-19 vaccine able to prevent the symptoms of the disease, it is also able to curb person-to-person transmission, according to data released by the U.S. Food and Drug Administration (FDA) on February 26. The findings bode well for federal, state, and local efforts to slash infection rates in the coming months. 

“A decrease in transmission is critical from a public health standpoint in that it will curb the spread of SARS-CoV-2 to others. So, rapidly vaccinating the general population will get us to herd immunity sooner,” Phyllis Tien, MD, professor of medicine in the division of infectious diseases at the University of California, San Francisco and a member of the National Institutes of Health’s COVID-19 Treatment Guidelines panel, tells Verywell. Tien was involved with a clinical trial of the new vaccine; she is not related to the author of this article.

One day after the transmission news broke, Johnson & Johnson’s Ad26.COV2.S vaccine followed Moderna’s mRNA-1273 vaccine and Pfizer/BioNTech’s BNT162b2 vaccine in becoming the third shot to receive emergency use authorization in the United States.

While all three of the vaccines significantly reduce symptomatic COVID-19 infection risk, their effects on asymptomatic COVID-19 infection risk have been little studied, hence the Centers for Disease Control and Prevention’s (CDC) recommendation that you continue to wear a mask, practice social distancing, and wash your hands frequently even after you’ve been fully immunized.

The new FDA data, however, suggests the risk of spreading COVID-19 after vaccination is low because the risk of asymptomatic infection is low. After all, you can't unknowingly transmit what you don't carry.

In a study by Janssen, the pharmaceutical division of Johnson & Johnson, the Ad26.COV2.S vaccine proved to be 74% effective against asymptomatic disease within 71 days compared to a placebo shot. When it comes to severe to critical disease, it is 77% effective within two weeks and 85% effective within four weeks.

What’s more, the Johnson & Johnson vaccine probably isn’t the only one capable of stopping the spread of COVID-19. In a study preprint seen by Reuters, Pfizer/BioNTech’s vaccine proved to be 89.4% effective against both asymptomatic and symptomatic disease and 93.7% effective against symptomatic disease alone.

But both Tien and Paul Spearman, MD, director of the division of infectious diseases at Cincinnati Children’s Hospital Medical Center and a member of the FDA’s Vaccines and Related Biological Products Advisory Committee, discourage comparisons at this point in time. They say that it is difficult to calculate efficacy objectively because the vaccines were tested at different times and in different populations, among other reasons. 

“These are all very positive indicators,” Spearman tells Verywell of the FDA data. (He clarified that he was speaking on behalf of himself rather than VRBPAC.) However, he adds, “we need to see [the studies] published in order to fully evaluate the findings. The importance, once this is verified, would be that not only do the vaccines reduce symptomatic disease, but that they prevent asymptomatic transmission.” 

While COVID-19 causes severe illness or death in some, it doesn’t affect others at all. Experts currently estimate that a fifth—around 17 to 20%—of all infections are asymptomatic. In short, you could be shedding viral particles all over the place at any given time without knowing it. 

Spearman says the prevalence of asymptomatic transmission is one of the reasons that this virus has been so hard to control.

"If you don’t feel like you have a virus, you may not take the right precautions to prevent spreading it to others," he says. "So a strong effect on transmission [such as that potentially conferred by the J&J vaccine] would be a major advantage in fighting the pandemic."

But 74% effective isn’t 100% effective. Consequently, Spearman does not expect the CDC to lift masking or social distancing guidance any time soon.

“There will still be unvaccinated individuals in the community who are susceptible and who can spread the virus...We have to think about those who are still susceptible and continue to mask and distance until spread is no longer occurring," he says. "This issue may be re-addressed by our public health experts after vaccines have been fully rolled out."

While slightly later on the scene than vaccines from Moderna and Pfizer/BioNTech, Johnson & Johnson has several major advantages over its predecessors. (Spearman calls it “an outstanding addition to the tools we have to protect the U.S. population” and says that he recommends it “without hesitation" on the grounds that it offers "very strong protection against severe disease, hospitalization, and death.") 

First, the Johnson & Johnson vaccine is a single-dose shot, meaning you don’t have to come back for seconds. Second, it can be stored in a refrigerator rather than in a heavy-duty freezer, meaning it is easier to store and transport long distances. These features, Tien says, “will get us to our goal of vaccinating the general population even quicker.” But even if they weren’t in the picture, the new vaccine would, in all probability, have received a warm welcome.

“Having a third vaccine in the mix will definitely help get more people vaccinated faster,” Tien says.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.