If you got the Johnson & Johnson COVID vaccine, will you need another shot? Experts say not to worry yet.

A new laboratory study suggests recipients of Johnson & Johnson’s coronavirus vaccine may need a second dose. Experts say: We’re not sure yet.

The study, which was posted by bioRxiv on Tuesday, found J&J’s vaccine to be less effective against the delta and lambda variants compared with the original virus. It suggests that a second dose, ideally of Pfizer or Moderna, might help increase protection.


The study has not yet been peer-reviewed or published, so experts say people who have received J&J’s shot shouldn’t worry about finding a second dose at the moment. More research and clinical studies are necessary to determine who needs booster shots and when.

Maryland’s Department of Health follows the policies of the U.S. Centers for Disease Control and Prevention and the federal Food and Drug Administration, which have not changed their guidance on the single-dose J&J vaccines.


The delta variant is now the most contagious form of the coronavirus, accounting for 83% of all new U.S. cases. Amid delta’s threat, climbing COVID cases and slowing vaccination rates, here’s what to know about the new research developments.

What are the findings?

The study was conducted with blood samples in a laboratory at New York University, comparing the performance of Pfizer’s and Moderna’s mRNA vaccines and J&J’s adenoviral vaccine against different virus strains. It found that J&J’s vaccine did not perform as well against the delta and lambda variants of the coronavirus compared with the original form of the virus.

“The message that we wanted to give was not that people shouldn’t get the J&J vaccine, but we hope that in the future, it will be boosted with either another dose of J&J or a boost with Pfizer or Moderna,” Nathaniel Landau, a virus specialist at NYU’s medical school who led the study, told The New York Times.

The findings line up with studies concluding that a single dose of the AstraZeneca vaccine, which is similarly structured to the J&J vaccine, is 33% effective against symptomatic disease from the delta variant. But they contradict studies published by J&J earlier this month that say a single dose is effective against the variant eight months after immunization.

Since the study is based on findings from a lab, it may not accurately represent how the vaccine works in the real world. Amesh Adalja, an expert in infectious diseases at Johns Hopkins, said lab-based studies often don’t paint the full picture of immunity.

“It doesn’t account for, for example, T-cell immunity,” Adalja said, referring to cells that play an important role in immune response. “It’s often better answered by a real-world study looking at people that have gotten the Johnson & Johnson vaccine and looking to see what happens to them clinically.”

Matt Laurens, a vaccine researcher at the University of Maryland School of Medicine, agreed that clinical data is crucial to determine who may need booster shots. He noted that multiple studies in the U.S. are continuing to follow people who have been vaccinated.

“If those individuals start to have increased numbers of cases, we’ll have data to know what viruses they were infected with and if we need to consider booster immunization,” Laurens said. “It’s just ... we want that data yesterday.”


What does this mean for those who were inoculated with J&J?

Adalja said before we draw any conclusions, the data from this study needs to be peer-reviewed and integrated with the contradictory findings from the studies published by J&J. He emphasized that the goal of vaccines is not to provide complete, sterilizing immunity, but to prevent serious disease, hospitalizations and deaths.

“All three of the vaccines are performing tremendously,” Adalja said. “I think we kind of got spoiled with very high efficacy against symptomatic disease and forgot what the actual purpose of the vaccines was.”

More than 99% of hospitalizations and deaths from the virus are among unvaccinated people, Adalja pointed out. The CDC is monitoring breakthrough cases in vaccinated people, but since May has solely focused on those who have been hospitalized.

At this point, Adalja said people who’ve been inoculated with the J&J should not try to get a second dose. He recommends people wait for more solid, clinical data.

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“I don’t think it harms people if they go get a second dose. But is it required? That I don’t think we have enough data to say,” Adalja said.

Laurens said physicians cannot recommend additional doses right now. If people are interested in receiving additional doses, he said, they can enroll as participants in studies. The University of Maryland Center for Vaccine Development is looking for volunteers for a mix-and-match booster study.


“If they want to help advance the science and help us answer that question, they can help by volunteering for studies,” Laurens said.

Will Maryland’s guidance on the J&J vaccine change now?

Charles Gischlar, spokesman for the Maryland Department of Health, said the state is not changing its guidance.

The state follows recommendations from the CDC and FDA. Maryland will continue providing one dose for J&J’s vaccine, and two doses for Pfizer’s or Moderna’s.

Gischlar said the department will not offer second shots to people who have received J&J’s vaccine.

“The J&J vaccine is a single-dose vaccine and this is recorded on an individual’s vaccine card,” he said.