The Johnson & Johnson Vaccine Explained

There are now three vaccines available to help protect people in the U.S. against Covid-19. That means there will be more vaccines to go around, increasing the number of people who can get vaccinated and bringing the world closer to the end of the pandemic.  

Late last year, the U.S. Food and Drug Administration authorized the use of two vaccines. The first was created by pharmaceutical companies Pfizer and BioNTech, and the second by Moderna (see “U.S. Authorizes First Vaccine for Covid-19,” Science World, December 11, 2020). Both of these vaccines require two doses, which must be taken a few weeks apart to be fully effective.

The most recent vaccine was created by the health-care company Johnson & Johnson. It works differently than the other two Covid-19 vaccines—and it only requires a single dose. That will help ensure people can get completely vaccinated faster.

The Pfizer-BioNTech and Moderna vaccines both rely on messenger RNA, or mRNA, to train the body to fight the SARS-CoV-2 virus that causes Covid-19. The mRNA molecules in the vaccines carry directions to make spike proteins found on the surface of the virus particles. The body’s disease-fighting immune system learns to recognize these proteins and attack any future SARS-CoV-2 virus particles it encounters (see “How Do Covid-19 mRNA Vaccines Work?” Science World, December 11, 2020).

Instead of using mRNA, the new Johnson & Johnson vaccine encodes instructions to make spike proteins using DNA molecules. Scientists packaged the DNA inside an inactivated and harmless form of the adenovirus—one of the many types of viruses that can cause the common cold. Once the vaccine is injected into a person, virus enters the body’s cells. The cells read the viral DNA and copy part of its code into mRNA, which is used to create spike proteins (see DNA vs. RNA). Just like with the Pfizer-BioNTech and Moderna vaccines, the foreign proteins trigger the body’s immune system to take action. The body’s immune cells will remember the invaders and respond to future exposures to the virus that causes Covid-19.

Experts see many advantages to the Johnson & Johnson vaccine compared with the others currently available. “Needing to take only one shot is an obvious plus,” says Sara Suliman, who studies immunology at Harvard University in Massachusetts. “This new vaccine is also a lot more temperature stable than the mRNA vaccines,” she explains. That means it can be stored in a standard refrigerator like one found in your home. Both of the mRNA-based vaccines, on the other hand, must remain frozen at ultra-low temperatures—Pfizer-BioNTech’s at -80°C (-112°F) and Moderna’s at -25°C (-13°F). That makes mRNA vaccines much more difficult to transport and store, particularly for rural or remote areas where doctors don’t have access to specialized freezers.

Johnson & Johnson’s vaccine is 72 percent effective in protecting against moderate to severe Covid-19. And even more important, none of the tens of thousands of volunteers who tested the vaccine were hospitalized or died of Covid-19. That shows that, so far, the vaccine is 100 percent effective at preventing the most serious Covid-19 cases. The Johnson & Johnson vaccine is also the first to be officially tested against one of the newer strains of the virus that causes Covid-19. The company found its vaccine to be 64 percent effective against a version of the virus that has appeared in places like the United Kingdom, South Africa, and the U.S.

Doses of Johnson & Johnson’s vaccine began shipping in March, almost immediately after it was authorized for use in the U.S. on February 27, 2021, for people age 18 and older. Government officials expect 100 million doses will be available by the end of June. But with so many people still waiting to be vaccinated, it’s likely they won’t be able to pick which version of the vaccine they receive. “If a person is able to get vaccinated, I suggest that they take whichever one is available, because all of the options work very well to limit severe Covid-19,” says Suliman.

While Covid-19 vaccines can prevent people from becoming seriously ill, it’s still not known whether the vaccines reduce the virus’s ability to spread from person to person. So doctors recommend that everyone who’s been vaccinated still practice social distancing, hand washing, and mask wearing.

On April 13, 2021, the CDC and FDA recommended pausing distribution of the Johnson & Johnson vaccine, after six recipients (out of 6.8 million total) developed severe blood clotting.

Update: As of April 23, 2021, the CDC voted to resume use of Johnson & Johnson’s vaccine, after reviewing the data and concluding that the benefits of the treatment outweigh the rare risk of blood clot. The FDA and CDC have issued a warning about the potential side effects, and will continue to monitor the safety of all Covid-19 vaccines.