Everything to know about Johnson & Johnson's COVID vaccine

A booster shot means a second shot for those who got J&J, but people living in San Francisco can get a third.

Jessica Rendall Wellness Writer
Jessica is a writer on the Wellness team with a focus on health news. Before CNET, she worked in local journalism covering public health issues, business and music.
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If you got Johnson & Johnson's COVID-19 vaccine and live in San Francisco, you can get another booster — even if you already got a second shot months ago. 

Third doses for people who got Johnson & Johnson aren't recommended by the US Centers for Disease Control and Prevention or authorized by the US Food and Drug Administration. Rather, it's a "local accommodation" by the San Francisco Department of Health to allow those who originally got the J&J to get a third dose.

Booster shots have been recommended for adults and teens because of the omicron variant's ability to reduce some infection protection of the COVID-19 vaccines (but still maintain protection against severe disease), but folks who originally opted for the one-dose shot have been told to get a second dose for months because one dose of Johnson & Johnson has a lower level of protection compared to two doses of Pfizer or Moderna vaccines. (Two doses of Johnson & Johnson, however, raises the protection of the vaccine to the same league as two doses of its mRNA cousins.) 

But everyone who originally received Johnson & Johnson's vaccine should get a booster shot of Pfizer or Moderna instead, the CDC says, citing the rare but serious risk of blood clots following Johnson & Johnson's shot (which doesn't happen with Pfizer's or Moderna's). However, if you prefer Johnson & Johnson's vaccine for any reason, it is still available. This "mix and match" approach to COVID-19 vaccine boosters has been authorized by the FDA and exercised by many Americans getting boosted the past few months. 

Here's what to know if you got the J&J. 


The definition of "fully vaccinated" hasn't changed. You're considered fully vaccinated after two doses of Moderna's or Pfizer's vaccine, or one dose of Johnson & Johnson's.

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What booster should I choose if I got Johnson & Johnson? 

You should get a Pfizer or Moderna booster, the CDC says, at least two months after your Johnson & Johnson vaccine. This "mix and match" approach for COVID-19 boosters was authorized by the FDA after early studies from the US and other countries found it's safe and effective. In fact, some research shows that people who originally got J&J's shot have a better response to Moderna's and Pfizer's booster than to another shot of Johnson & Johnson. 

Boosters are recommended for everyone age 12 and up for maximum protection against the omicron variant, which appears to lower the effectiveness of all the COVID-19 vaccines, as well as protection from past COVID-19 infections. 

However, you can still receive Johnson & Johnson's booster if you choose. The reason that the CDC is now recommending Pfizer and Moderna over Johnson & Johnson is because neither mRNA vaccine carries the rare but dangerous blood-clotting side effect, and both also appear to be more effective than J&J. What's more, vaccines are widely available in the US now, unlike earlier in the pandemic when the public health advice was to get whatever vaccine you could as soon as you could. 

Should I be worried about blood clots if I got J&J?

If you got your Johnson & Johnson shot more than four weeks ago, you are not at increased risk of side effects, CDC Director Dr. Rochelle Walensky tweeted. So, if you got your Johnson & Johnson shot months ago, there is no cause for concern. Symptoms of the blood-clotting disorder typically appear within one to two weeks after receiving the vaccine, according to a fact sheet by the FDA

Although cases of the blood-clotting disorder that occurs after vaccination with Johnson & Johnson's and AstraZeneca's vaccine are rare and have occurred in men and women (according to a December CDC presentation, 54 cases in the US were reported through August out of millions of doses given), the risk is higher for women ages 30 to 49, occurring in one in 100,000 women. 

The vaccine-induced blood clots, TTS, also require different treatment and appear to be more fatal than other blood clots that can happen in people more at risk because they take birth control pills, for example. Cases of TTS after vaccination have been fatal in 15% of cases, the FDA says, or about one in seven people. All cases of TTS required hospitalization or ICU admission, nine people have died and some needed to be treated at a post-acute care facility after their hospitalization. 

If you received Johnson & Johnson within the last few weeks, know that TTS is a rare event, but symptoms of it include: blurred vision, intense headache, shortness of breath, changed mental status, chest pain, persistent abdominal pain, leg swelling, weakness on one side of the body and easy bruising or tiny blood spots away from the injection site, according to CDC information. If you experience symptoms, seek medical care immediately. 

Another side effect people might be at increased risk of following vaccination with Johnson & Johnson is Guillain-Barre syndrome, an autoimmune disorder that can also be triggered by viruses. According to a July presentation by a CDC committee, 98 cases of the syndrome were reported, and one person died. In general, Guillain-Barre is more common in men and adults over 50, according to the CDC. 

In a December statement, Johnson & Johnson said the company "remains confident in the overall positive benefit-risk profile of its COVID-19 vaccine." 

"The safety and well-being of those who use the Johnson & Johnson vaccine continues to be our number one priority," Dr. Mathai Mammen, the global head of research and development said in the statement. "We appreciate today's discussion and look forward to working with the CDC on next steps."

But don't we need J&J? 

Johnson & Johnson's vaccine is easier to store than Pfizer's and Moderna's vaccines. It's also the only one-dose COVID-19 vaccine authorized by the FDA, which has made it an attractive option to give out in places such as homeless shelters, prisons, airport vaccine clinics and to people living in "hard-to-reach" communities who may not be able to show up for a second dose. Also, it's an alternative to mRNA vaccines, which has contributed to vaccine hesitancy in some people (the new CDC guidance doesn't mean you can't get J&J now). 

However, some experts on the CDC panel questioned Johnson & Johnson's status as a one-dose treatment as a reason to recommend the vaccine, given that everyone who received it is being told to get a COVID-19 booster sooner than those who got Moderna or Pfizer because of its lower effectiveness. If people living in communities that don't have as much access to health care continue to be given a vaccine scientists say isn't as good, it could worsen health care inequities in the country. 

"It's not all about ease," pediatrician and CDC committee member Dr. Pablo Sanchez said in December. "It is not a single-dose vaccine anymore." 

Even if the CDC's new guidance for Johnson & Johnson's vaccine levels the playing field in the US, it may contribute to problems abroad. CDC members also raised questions Thursday about how the US' recommendation on Johnson & Johnson will impact distribution around the world. 

"We are fortunate to have other vaccines available," said Lynn Bahta, a CDC committee member and immunization program clinical consultant.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.