[Originally published: Oct. 18, 2021. Updated: July 20, 2022.]
Note: Information in this article was accurate at the time of original publication. Because information about COVID-19 changes rapidly, we encourage you to visit the websites of the Centers for Disease Control & Prevention (CDC), World Health Organization (WHO), and your state and local government for the latest information.
In May, the Food and Drug Administration (FDA) put new restrictions who can get the Johnson & Johnson vaccine, based on a fresh review of data on the life-threatening blood clots that have been associated with the vaccine.
The FDA’s latest decision restricts access of the vaccine to adults 18 and older who specifically request the J&J shot or who cannot have the other available vaccines for medical reasons.
Anyone who got the Johnson & Johnson shot should take advantage of the Centers for Disease Control & Prevention’s (CDC’s) “mix-and-match” policy that allows them to choose one of the mRNA vaccines for their booster.
The decision to recommend mRNA vaccines was an important one, since early data showed a booster shot provided a much-needed advantage against the highly contagious Omicron variant. But so far that data is based on early studies of the Pfizer and Moderna boosters.
And before Omicron’s spread, early data from a federal clinical trial suggested it might be better for J&J one-shot recipients to get an mRNA vaccine booster. The trial’s preliminary data showed that people who had gotten the J&J vaccine followed by a Moderna booster had a 76-fold rise in antibodies in 15 days; those who got Pfizer saw a 35-fold increase; while those who got the J&J booster had only a fourfold increase. That data was published in a preprint and has not yet undergone independent peer review.
In light of the issues surrounding the Johnson & Johnson vaccine, we sat down with Yale Medicine infectious disease and community health doctors, who answered commonly asked questions.
1. Why did the CDC recommend the mRNA vaccines over J&J?
In December, the CDC recommended a preference for the two mRNA vaccines over J&J in response to concerns that had been building over a small, but growing number of cases of a rare, but serious clotting disorder in people who’d gotten the shot. In April 2021, the agency put a two-week pause on the vaccine while the matter was investigated. The pause was then lifted, but concern grew as more cases were reported.
The clotting disorder is called thrombosis with thrombocytopenia syndrome (TTS), and it is rare—an updated safety analysis showed that, as of March 18, out of 17 million people who got J&J, 60 cases of TTS were reported and nine people died. The analysis was based on suspected cases of TTS reported to the government’s Vaccine Adverse Event Reporting System (VAERS). The FDA updated its fact sheet on the shot.
The FDA also attached a warning to the J&J vaccine in July, after reports linked the vaccine to Guillain-Barré syndrome, a rare neurological disorder. For both warnings, the agency said the incidence was very rare, and the benefits of the vaccine still outweighed the risks.
All three vaccines available in the United States have had reports of rare adverse events. The FDA added warnings to the Pfizer and Moderna vaccines following reports of rare cases of myocarditis and pericarditis after mRNA vaccination, particularly in male adolescents and young adults.
2. How did J&J boosters get authorized for use?
Early in 2021, when Johnson & Johnson's vaccine was authorized for use in the United States, some people expressed concern about the efficacy of the single-shot vaccine, which trailed behind the Pfizer and Moderna vaccines, based on data from their clinical trials at that time. (Pfizer’s and Moderna’s two-dose primary series were each around 94% protective against symptomatic disease; J&J’s was 66% [in all of the countries studied] and about 72% in the U.S. alone.)
Later in the year, in early October, the CDC approved the Johnson & Johnson booster after the company shared data—including 94% efficacy against symptomatic disease after a booster—that put its vaccine on par with the mRNA COVID-19 vaccines from Pfizer-BioNTech and Moderna. (The Moderna booster was also approved in October—Pfizer’s booster had been approved earlier, in September.)
Initially the two mRNA vaccines were available only to certain at-risk populations, but that was later revised so that anyone who had gotten the primary dose of one of the three vaccines was eligible for a booster.
Still, far more people in the U.S. got vaccinated with the Pfizer or Moderna vaccines. As of December 2021, about 16 million Americans were fully vaccinated with the J&J vaccine, compared to more than 73 million who received Moderna and 114 million who received Pfizer, according to the CDC.
3. What has the J&J booster data shown?
For an FDA panel meeting in October to discuss authorization of its booster, J&J provided post-booster data from a large global study. The company reported that, in addition to providing 94% protection against moderate-to-severe COVID-19 in the U.S. (that figure was 75% in all of the countries studied), a booster shot given two months after the initial dose increased antibody levels by four to six times, compared to one dose alone.
Another report, a real-world study from the CDC conducted from March through August, showed the J&J single shot to be only 71% effective against hospitalization from COVID-19 in U.S. adults without immunocompromising conditions, compared to 93% for Moderna and 88% for Pfizer. “But with the booster dose, the J&J vaccine could be equivalent to the mRNA vaccines,” Leslie Sude, MD, a Yale Medicine pediatrician who has helped provide vaccinations, said at the time. “Some vaccine experts feel that the J&J vaccine should have always been a two-dose series, but have only recently reached the phase of vaccine efficacy monitoring to confirm that idea.”
As far as Omicron, the data is still coming in. Most recently, in late December, a study showed that the Johnson & Johnson shot, China's Sinopharm vaccine, and Russia's Sputnik V (the latter two of which are not approved for use in the U.S.) showed no neutralizing activity against Omicron. The study has not yet been peer-reviewed.
4. Why did the FDA question the strength of J&J’s booster data?
Even though the FDA advisory panel unanimously recommended authorization of Johnson & Johnson’s booster in October, it also questioned a test used in the trial to support its application for authorization. Regulators questioned the accuracy of a test called pseudovirus neutralization assay (psVNA), which is used to measure antibodies, suggesting that the low-test sensitivity could have affected the results of the clinical trial.
“The upshot, though, is that despite the concern for low sensitivity of the psVNA, the advisory panel still recommended the second dose,” said Dr. Sude at the time. “They feel that everyone who received a first dose should be given the option to optimize protection based on the best data available at the time.”
5. Should you still choose the J&J vaccine?
The CDC has expressed a preference for the mRNA vaccines over Johnson & Johnson in most situations. A fourth choice became available in July with the authorization of the Novavax vaccine. But if the J&J vaccine is your only choice, the benefits of getting any vaccine still outweigh the risks of being infected and becoming severely ill from the coronavirus.
Booster shots are important too. If you got J&J as your initial vaccine and are 18 or older, you are eligible for a booster shot two months later, regardless of which one you choose. You’re eligible six months later if you are had Moderna or Pfizer-BioNTech as your primary series (and a Pfizer booster is now available for children ages 5 and up). The CDC provides further guidance on getting a booster shot. Some people should also get a second booster.
Note: Information provided in Yale Medicine articles is for general informational purposes only. No content in the articles should ever be used as a substitute for medical advice from your doctor or other qualified clinician. Always seek the individual advice of your health care provider with any questions you have regarding a medical condition.