A pharmacist holds a vial of the Johnson & Johnson COVID-19 vaccine at a hospital in Bay Shore, N.Y., on March 3, 2021.
A pharmacist holds a vial of the Johnson & Johnson COVID-19 vaccine at a hospital in Bay Shore, N.Y., on March 3, 2021. (Mark Lennihan/AP)

An unusually intensive, three-way comparison of the Pfizer, Moderna and Johnson & Johnson Covid-19 vaccines shows the body’s antibody response spikes sharply and then falls off after receiving the two mRNA vaccines but stays lower and steadier after the Johnson & Johnson vaccine.

Johnson & Johnson presented the research letter, also published Friday in the New England Journal of Medicine, as part of its request to the US Food and Drug Administration for emergency use authorization for a booster dose for its one-shot vaccine.

The FDA’s vaccine advisory committee is meeting to decide whether to recommend a booster dose for J&J’s vaccine.

Researchers looked at the blood of 61 volunteers who got either Pfizer’s, Moderna’s or J&J’s vaccine, testing various immune responses two to four weeks after vaccination, at six months and at eight months. They looked at a variety of antibody responses, as well as at immune cells called T cells. 

“It’s a small study. It needs to be confirmed by larger studies, but it’s a detailed immunological analysis with lots of different types of antibody testing,” Dr. Dan Barouch, a vaccine researcher at Beth Israel Deaconess Medical Center and Harvard Medical School who led the research team, told CNN. 

Pfizer’s vaccine produced a peak antibody response at two weeks that declined sharply by six months and even more by eight months, the research team found. Moderna’s vaccine elicited a much higher neutralizing antibody response than Pfizer’s — three times as high as Pfizer’s at peak — but this also dropped dramatically by eight months.

In contrast, the J&J vaccine did not elicit a very high antibody response at first but this response also did not drop off over time. It’s not entirely clear what any of this means in terms of protecting people from infection. The study notes that it has yet to be established which types of antibody responses correlate with real-life protection from infection and severe disease. However, studies have indicated that as neutralizing antibody levels drop, protection from mild infection also drops while people remain protected from severe disease and death.

“So I think the argument for boosters are different for the mRNA vaccines and for the J&J vaccines,” Barouch said. “For the mRNA vaccines, they started off at 94, 95% efficacy and then, at least for Pfizer, we’ve seen that efficacy go down. And so the argument for the booster for the mRNA vaccines that antibody titers are waning quickly and at least for Pfizer, there’s been an erosion of protection, seen clinically at least, at least for mild disease.” 

J&J has reported separately that boosting its one-dose vaccine brings the efficacy up from about 70% to 94%. 

“What will really change the arc of the pandemic is to get the unvaccinated people vaccinated for the first time, and that that needs to remain the priority,” Barouch said. “Discussion of boosters is good, and likely beneficial for certain individuals, but that has to be a second level priority.”

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