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A small laboratory study suggests that Johnson & Johnson’s single-shot COVID-19 vaccine provides robust protection against eight variants, including Delta, the highly infectious form of the virus that now represents about a quarter of all confirmed US coronavirus cases.

Blood serum drawn from eight volunteers who received the shot in a clinical trial at Beth Israel Deaconess Medical Center late last year generated high levels of neutralizing antibodies against each of the variants, according to Dr. Dan Barouch, who runs the Boston hospital’s Center for Virology and Vaccine Research and helped develop the vaccine.

Serum drawn from eight other people who received two shots of the vaccine, an experimental regimen that researchers are studying in a late-stage clinical trial, produced comparable levels of antibodies against each variant, he said.

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“These data are encouraging,” said Barouch, lead author of a 16-page paper that was posted on a preprint server but has yet to be published in a peer-reviewed journal.

Researchers believe that high levels of antibodies indicate likely immunity to the coronavirus, but that has yet to be definitively proven 18 months into the pandemic.

The study also found that protective antibodies and other components of the immune response, including T cells, remained robust over eight months and may become stronger against some variants over time, Barouch said.

Johnson & Johnson’s vaccine was approved by the Food and Drug Administration in February for emergency use. Vaccines from Pfizer-BioNTech and Cambridge-based Moderna received FDA emergency clearance in December.

The paper on the Johnson & Johnson vaccine represents more reassuring news that the three COVID-19 vaccines are likely to protect recipients from worrisome variants, including Delta, which was first detected in India.

Moderna said Tuesday that its vaccine produced neutralizing antibodies against seven variants first identified in Angola, India, Nigeria, South Africa, and Uganda in a laboratory test. That study used blood serum drawn from eight vaccinated volunteers.

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A much larger Public Health England study published in May found that two doses of Pfizer’s vaccine were 88 percent effective against the Delta variant among people who had received the shots and went about their lives.

Only about 8 percent of the more than 155 million fully vaccinated people in the United States have received the Johnson & Johnson vaccine, according to the US Centers for Disease Control and Prevention. More than 52 percent have received the Pfizer vaccine, and over 39 percent the Moderna vaccine.


Jonathan Saltzman can be reached at jonathan.saltzman@globe.com.