How effective is the J&J vaccine against the Delta variant? Expert says it’s ‘too soon’ to tell

Close-up of a young woman getting vaccinated.

Three weeks after Johnson & Johnson (J&J) released a set of studies showing that its single-shot COVID-19 vaccine "generated strong, persistent activity against the rapidly spreading Delta variant," a new preprint from researchers at New York University suggests that it may be less effective at fighting off the new strain than suggested.

The news comes as the U.S. enters another wave of the COVID-19 pandemic, driven largely by the Delta coronavirus variant, which the Centers for Disease Control and Prevention say now accounts for more than 83 percent of cases. Still, experts say that those claiming that the J&J vaccine is simply not effective against the Delta variant are jumping to conclusions. 

"It's a little too soon to say," says Dr. Gregory Poland, co-director of the Mayo Clinic's Vaccine Research Group. "Eighty-eight percent of the hospitalizations in the U.S. due to COVID are unvaccinated people. But what's key is the converse. Twelve percent of them have been vaccinated and yet admitted to the hospital. I don't know which vaccines they got. I don't know if they were fully vaccinated. I don't know if they were immunocompromised. This is the data void we have to fill in order to be definitive."

Poland and others who have pushed back on claims about the J&J vaccine not being effective against the COVID-19 variants have good reason to be skeptical. The paper this claim is based on — a paper that has not been peer-reviewed — is far from bulletproof. In the study, researchers tested the blood of 17 people who received the mRNA vaccines and 10 people who received the J&J vaccine, looking to see which antibodies were best able to fight off COVID-19 (and, in particular, variants like Delta).

The mRNA vaccines such as Moderna and Pfizer came out on top, but Poland says that doesn't necessarily dispute J&J's earlier findings of strong immunity. "What we have are two reports, a press report from J&J and a preprint paper," says Poland. "Both of these reports involve very small numbers of people and laboratory-based [tests] from which they extrapolate what the meaning of this might be in the real world."

BioRxiv, the preprint site where the paper was published, also included a disclaimer: "bioRxiv posts many COVID19-related papers. A reminder: they have not been formally peer-reviewed and should not guide health-related behavior or be reported in the press as conclusive," the note reads.

In a statement to Yahoo, a spokesperson from J&J also urged caution. "While the [study] provides some insight into a single aspect of immune response engendered by COVID-19 vaccines, the data do not speak to the full nature of immune protection," the spokesperson wrote. "The dual mechanisms of protection against COVID-19 that are generated by the Johnson & Johnson COVID-19 vaccine, both neutralizing and non-neutralizing binding antibodies and multiple kinds of T-cells, play a cooperative role in combating SARS COV-2."

The authors of the NYU study could not be reached for comment by the time of publication but shared their motivation for the study with the New York Times. “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, leader of the study and virologist at the NYU Grossman School of Medicine, told the New York Times.

It's not the first time that the idea of an additional shot has been floated. While the CDC has not yet issued any official recommendations, experts have begun recommending that individuals who had gotten the J&J vaccine consider getting a single dose of the Moderna or Pfizer vaccine as a "booster" to their immunity. Although the vaccines use different mechanisms, all three are training the body to recognize the spike protein on the surface of the SARS-CoV-2 virus, meaning there's a good chance that adding another vaccine could be beneficial. 

Poland isn't opposed to boosters becoming the norm. "If I had to guess ... we're going to find that if you got one dose of J&J, you're going to need a second dose, either another J&J or an mRNA," says Poland. "But no one knows that for sure yet." More research is needed to determine whether it is the right course of action, but a study earlier in July on mixing vaccines provided compelling evidence that it will work.

While that's an exciting prospect, Poland reinforces that at this stage — as the pandemic begins to spike again — it's the unvaccinated population who should be the focus of concern. "For people who got fully vaccinated, there's almost no chance that they're going to die or have a severe infection," says Poland. In other words: Right now, any vaccine is better than none at all. 

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