The Johnson & Johnson-made coronavirus vaccine is much less effective against the Delta and Lambda variants than against the original virus, according to a new study posted online Tuesday.
The findings add to the evidence that the 13 million people who have been vaccinated with the J.&J. vaccine may need to be given a second dose — ideally from one of the mRNA vaccines made by Pfizer-BioNTech or Moderna, the authors said.
But the conclusions contradict those of smaller studies published by Johnson & Johnson earlier this month that suggest a single dose of the vaccine is effective against the variant even eight months after inoculation.
The new study has not yet been peer-reviewed or published in a scientific journal and was based on lab experiments. But it’s consistent with observations that a single dose of the AstraZeneca vaccine — which has a similar architecture to the J.&J. vaccine — shows only about 33 percent efficacy against symptomatic disease caused by the Delta variant.
“The message we wanted to give was not that people shouldn’t get the J.&J. vaccine, but we hope it will get a boost in the future with or another dose of J.&J. or a boost with Pfizer or Moderna,” said Nathaniel Landau, a virologist at NYU’s Grossman School of Medicine who led the study.
Other experts said the results are what they expected, as all vaccines seem to work better when given in two doses. “I have always thought, and often said, that the J.&J. vaccine is a two-dose vaccine,” said John Moore, a virologist at Weill Cornell Medicine in New York.
dr. Moore pointed to several studies in monkeys and humans that have shown greater efficacy with two doses of the J.&J. vaccine, compared to one dose. He said the new study was particularly credible because it was published by a team unrelated to any of the vaccine manufacturers.
But the data from the new study “doesn’t speak the full nature of immune protection,” said Seema Kumar, a spokeswoman for J.&J. Studies sponsored by the company indicate that the vaccine “generated strong, sustained activity against the rapidly spreading Delta variant,” she said.
The Delta variant is the most contagious version of the coronavirus to date. It accounts for 83 percent of infections in the United States, said Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, during a Senate hearing on Tuesday.
The variant may also be primarily responsible for a recent increase in infections: While still low compared to last winter, cases are increasing in all 50 states and hospitalizations are increasing in nearly all states. In the two weeks ending Tuesday, the country had an average of 268 deaths a day.
Delta can cause more breakthrough infections than previous forms of the virus, but more than 99 percent of hospitalizations and deaths occur among unvaccinated people. Vaccination rates in the country have stalled, with just under 60 percent of adults fully protected against the virus.
Several studies have suggested that the mRNA vaccines made by Pfizer-BioNTech and Moderna will retain their efficacy against the coronavirus, including all variants identified so far. For example, a recent study showed that the vaccines trigger a sustained immune response in the body that can protect against the coronavirus for years.
But evidence on the J.&J. vaccine is limited, as it was rolled out later than the mRNA vaccines. Most studies on the effectiveness of the coronavirus vaccines were conducted in medical centers and hospitals based on samples from employees who received the mRNA vaccines.
The J.&J. vaccine was also dogged by reports of blood clots and a rare neurological syndrome, as well as problems with contamination at a Baltimore factory.
Small studies published by researchers associated with J.&J. suggested that the vaccine was only slightly less effective against the Delta variant than against the parent virus, and that the vaccine-stimulated antibodies became stronger in eight months.
The team of dr. Landau probably would have seen a similar increase in the vaccine’s potency had they looked at the data over time, said Dr. Dan Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston. The data on the J.&J. The vaccine’s strength against the Delta variant at day 29 is not much different from that reported in his own study, said Dr. barouch.
“Basically, I don’t see there being any disagreement,” he said. “The question is that of the kinetics, it’s not just the magnitude, because immune responses are not static over time.” The new study also didn’t take into account other components of the immune defense, he added.
dr. Landau and his colleagues looked at blood samples from 17 people immunized with two doses of an mRNA vaccine and 10 people with one dose of the J.&J. vaccine.
The J.&J. vaccine started out with lower efficacy than the mRNA vaccines and showed a greater drop in efficacy against the Delta and Lambda variants. “The lower baseline means what’s left to counter Delta is very weak,” said Dr. Moore. “That’s a big concern.”
Very few vaccines are given as a single dose because the second dose is needed to raise antibody levels, noted Akiko Iwasaki, an immunologist at Yale University. People who have been vaccinated with the J.&J. vaccine “relying on that primary response to maintain high levels of antibodies, which is difficult, especially against the variants,” she said.
Boosting immunity with a second dose should raise antibody levels high enough to counteract the variants, she said.
As for an mRNA vaccine for the second injection, instead of another J.&J. injection, may be better: Several studies have shown that combining one dose of the AstraZeneca vaccine with a dose of the Pfizer-BioNTech or Moderna vaccines stimulates the immune response more effectively than two doses of AstraZeneca.
The Food and Drug Administration has said, “Americans who are fully vaccinated do not need a booster shot at this time,” and the agency is unlikely to change its recommendations based on lab testing. But the new data should prompt the FDA to reconsider its recommendations, said Dr. Landau: “I hope they read our article and think about it.”