If you received the J&J COVID-19 vaccine, here's what you need to know now

Artur Widak
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Almost 17 million Americans have received the Johnson & Johnson COVID-19 vaccine — equivalent to the populations of New York City, Los Angeles, Chicago and Philadelphia combined — a huge number that seems to have been forgotten in a country dominated by Pfizer and Moderna recipients.

The single J&J Janssen shot was initially touted for its convenience and accessibility — a one-and-done regimen that didn’t require ultra-cold storage.

But there were questions about its efficacy compared to the two-shot mRNA vaccine series and concern about the risk of rare blood clots. The Centers for Disease Control and Prevention now calls the Pfizer and Moderna vaccines the “preferred” options over J&J in most situations.

There has always seemed to be less guidance for recipients of the least-used vaccine. So if you’ve already gotten the J&J shot or are still considering it, what’s the latest on the protection it provides and whether you need more shots?

TODAY asked Dr. Daniel Kuritzkes, chief of the division of infectious diseases at Brigham and Women’s Hospital in Boston and professor of medicine at Harvard Medical School; and Dr. Roy Gulick, chief of the division of infectious diseases at NewYork-Presbyterian/Weill Cornell Medical Center and professor of medicine at Weill Cornell Medicine.

Are you still considered fully vaccinated with one J&J shot?

Yes, a person who has received a primary series of a COVID-19 vaccine — a single-dose, in the case of J&J’s vaccine — is considered fully vaccinated, according to the CDC.

“I think that’s in sore need of updating,” Kuritzkes said. “Practically speaking, based on the totality of the data, I would consider that a single shot of the J&J vaccine is inadequate to provide full protection.”

The CDC has moved towards the terminology of staying “up to date” with your vaccines, which means additional shots.

What do we know about J&J’s protection now?

A study published by Centers for Disease Control and Prevention on March 29 looked at how effective the vaccine was at preventing emergency room and urgent care visits.

It found:

  • one dose of J&J was only 24% effective.

  • two doses were 54% effective.

  • one dose of the J&J vaccine plus one dose of an mRNA booster were 79% effective.

  • that compared to 83% effectiveness after three mRNA doses.

The paper was based on data from 10 states and covered the time from mid-December 2021 to early March 7, 2022, when omicron was the predominant variant.

When it came to how effective the J&J vaccine was at preventing COVID-19–associated hospitalization during that period, the study found:

  • one dose was 31% effective.

  • two doses were 67% effective.

  • one dose of the J&J vaccine plus one dose of an mRNA booster were 78% effective.

  • that compared to 90% effectiveness after three mRNA doses.

But there have been other studies showing better results for the J&J vaccine, with protection that's more durable than the mRNA options.

A study published March 17 in JAMA Network Open estimated a single J&J shot was 76% effective at preventing COVID-19 infection and 81% for hospitalizations for at least 180 days.

Other data from the CDC showed that from late December through Feb. 19, the weekly rate of breakthrough cases was lowest among people who got the J&J shot.

Besides stimulating the immune system to produce antibodies, vaccines also induce T cells, another layer of protection.

“The major plus for the J&J vaccine is that it does induce very high levels of cytotoxic T cells. These are cells that are instructed to kill virus-infected cells,” Kuritzkes said.

The T cells are persisting whether or not antibody levels are decreasing, which may explain why J&J’s level of protection appeared to remain pretty stable at six months compared to the decline observed for the mRNA vaccines — though they still started off with a higher level of protection, he noted.

Studies continue on how durable and stable the protection of all the vaccines is.

How should you be boosted if you’ve had the J&J vaccine?

You can receive a booster dose at least two months after getting the initial shot. Booster doses from Pfizer or Moderna are preferred, the CDC said.

“For J&J, there is some data to suggest that antibody levels are better if you switch to the mRNA vaccine and in particular Moderna, so many people will opt for that choice to get higher antibody levels,” Gulick said.

You can also get a second J&J shot as a booster.

On March 29, the CDC announced that adults who received a primary vaccine and booster dose of J&J at least four months ago can now receive a second booster dose using an mRNA COVID-19 vaccine.

“We found that any booster strategy is better than a single J&J dose, which should encourage anyone who has only had a J&J vaccine to get a second COVID-19 vaccine as soon as possible, especially before the expected next surge in COVID,” said Brian Dixon, senior author of the new CDC study and an associate professor at the Indiana University Richard M. Fairbanks School of Public Health.

“Individuals with three doses of mRNA had the strongest level of protection against severe consequences from the disease, but being boosted made a significant difference in protection for those who had J&J vaccines.”

If you had the J&J vaccine without any blood clot problems, is it OK to get the second shot?

It’s unclear, the experts said. The vaccine has been linked to the risk of rare but potentially life-threatening blood clots. At least 54 people in the U.S., mostly younger women, have been hospitalized from these blood clots, and nine people have died.

For those considering a J&J booster, the risk may linger even if they experienced no problems with the initial shot.

“Just because that didn’t happen the first time around, I’m not sure you could guarantee it wouldn’t happen the second time around,” Kuritzkes said.

“If you were an older person or a man and wanted to get a boost of J&J and you did fine with the first the shot, it’s probably fine. I would still have some hesitation if I were a young woman getting boosted with the J&J.”

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