Medical Experts Weigh In: What to Know About Johnson & Johnson’s COVID-19 Vaccine

Update as of April 13, 2021: The U.S. Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) have recommended a pause in the use of the Johnson & Johnson (J&J) COVID-19 vaccine. The agencies are reviewing data tied to six cases of a rare and severe type of blood clot in combination with low levels of blood platelets among individuals who received the J&J vaccine. While these events seem to be extremely rare, the CDC and FDA are recommending a pause in using the J&J vaccine out of an abundance of caution. Please contact your health care provider if you have received the J&J vaccine within the last three weeks and develop severe headache, abdominal pain, leg pain or difficulty breathing. We will continue to monitor and provide updates as the situation evolves. Please visit the CDC’s website for additional information. 

As of mid-March, about 70 million, or 21% of the U.S. population, have received at least one dose of a COVID-19 vaccine. Since their approvals in December, the Pfizer/BioNTech and Moderna COVID-19 vaccines have made up the bulk of this effort. Recently, the Food & Drug Administration (FDA) authorized Johnson & Johnson’s single-dose COVID-19 vaccine for emergency use in individuals 18 years of age and older, adding a third vaccine option to the race against the virus.

Johnson & Johnson’s vaccine comes at a pivotal time for the U.S., which earlier this year surpassed 500,000 COVID-related deaths in a pandemic that has lasted over a year. As the U.S. currently grapples with new, more infectious virus variants, the addition of a third vaccine to market is a key milestone in the nation’s inoculation efforts. It also marks a critical step toward giving more people access to the first-ever single-dose COVID-19 shot.

“The authorization of the J&J vaccine is exciting news for all of us,” says Dr. Jeannie Kenkare, chief medical officer and founder of PhysicianOne Urgent Care. “It means that we will have wider vaccine distribution and availability so we can get more Americans vaccinated as quickly as possible.”

All of the three vaccines available seem to give high/full protection against hospitalization and death from COVID-19. Beyond that important protection, the Johnson & Johnson vaccine is different in several key ways. As it is rolled out across the nation, questions around efficacy and distribution are top of mind for people who are eligible to get the vaccine. We’ve gathered insights and guidance from infectious disease specialists and medical experts throughout New England to answer some of the biggest questions about the Johnson & Johnson vaccine.

How does Johnson & Johnson’s vaccine work?

The Johnson & Johnson vaccine is the first approved coronavirus shot in the U.S. to use an older technology – i.e., viral vectors. This vaccine platform has been used several times in the past for vaccines, notably in response to Ebola outbreaks in July 2020. The viral vector platform is known to have a very good safety profile from its past use.

Johnson & Johnson’s COVID-19 vaccine is made from an inactivated adenovirus, a virus that typically causes colds or flu-like symptoms and contains a piece of DNA which instructs the body to produce the COVID-19 spike protein. By doing this, the vaccine causes the immune system to react more strongly to the spike proteins, which then increases protection against the virus. Importantly, nothing in the vaccine is alive and can infect you or become part of your DNA.

How does the Johnson & Johnson vaccine differ from the Moderna and Pfizer/BioNTech vaccines?

The main difference between all three vaccines is that the Johnson & Johnson vaccine is a viral vector vaccine, while the Moderna and Pfizer/BioNTech vaccines are both mRNA vaccines. Unlike viral vector vaccines, mRNA vaccines help create a protein in the body and instruct cells to create the “spike protein”– a protein found on the surface of the virus that causes COVID-19. Additional key differences include:

Dosage. Both the Moderna and Pfizer/BioNTech vaccines require two shots: a first dose, followed by a booster shot several weeks later (28 days later for Moderna and 21 days later for Pfizer/BioNTech). The Johnson & Johnson vaccine only requires a single dose, which is critical when vaccines are in short supply.


Storage. Unlike the Pfizer/BioNTech vaccine, which needs to be transported and stored at extremely low temperatures, the Johnson & Johnson vaccine is compatible with standard vaccine storage and distribution channels. It can safely be kept in a refrigerator for up to three months, which is much longer than the Moderna vaccine, which can expire after a month if not kept frozen.


Efficacy. The Johnson & Johnson vaccine proved to be 72% effective in the U.S. clinical trials, whereas the Moderna and Pfizer/BioNTech vaccines had efficacy rates of 94.1% and 95% respectively in clinical trials. Although the Johnson & Johnson efficacy rate is lower than the other two COVID-19 vaccines, the rate is still above the threshold (greater than 50%) originally set by the FDA for a vaccine to be considered useful. In fact, the Johnson & Johnson vaccine is much more effective than the annual flu shot, which typically has a 40-60% efficacy rate.


Overall, the key metric for these vaccines is the decrease in hospitalizations and death. Across its clinical trials, the Johnson & Johnson vaccine showed 85% efficacy against severe forms of COVID-19 and was 100% effective in preventing hospitalization and death from COVID-19. Dr. Patricia Toro, associate medical director of Harvard Pilgrim Health Care and infectious disease specialist, believes that efficacy shouldn’t be the only factor people consider when it’s their time to get the vaccine. “Comparing the efficacy of all three vaccines is challenging because the clinical trials were conducted in different populations and – in the case of the J&J vaccine – were tested on two key variants of concern,” says Dr. Toro.


“In contrast to the Pfizer and Moderna mRNA vaccines that are based on a brand-new technology, the new J&J vaccine is based on the same technology used for other vaccines, which allows it to be manufactured much more rapidly and does not require the extremely cold storage conditions needed for the two mRNA vaccines,” explains Dr. Richard Ellison, epidemiologist of UMass Memorial Medical Center. “It also offers the advantages of requiring only a single immunization to provide protection with less local and systemic side effects.”

Will I be able to choose one vaccine over the other?

With three vaccines on the market and distribution ramping up, many people are wondering if it will be possible to choose which vaccine they receive when it’s their turn, or if one is better than the other. Right now, many places don’t inform people far ahead of time about which vaccine they will get during the appointment. While it’s still early in the vaccine rollout, medical experts believe it will be highly unlikely that people will have a choice.

All three vaccines are currently authorized in the U.S. and have shown to be effective at preventing severe illness, hospitalization and death — which will play an integral part in keeping people safe and freeing up hospital capacity. It is important that people get the vaccine when it is their turn, regardless of which one is offered to them. Getting the vaccine will help protect against COVID-19 and help us collectively reach herd immunity sooner.