A second dose of Johnson & Johnsonʼs vaccine substantially increases its protection against COVID-19, said J&J in a statement. The New York Times reports that researchers found that two doses of the vaccine delivered 94% efficacy against mild to severe COVID-19 in the United States, up from 74% conferred with a single shot.
And two shots showed 100% efficacy against severe disease, although that estimate had a wide range of uncertainty.
The data have been submitted to the Food and Drug Administration, Johnson & Johnson said.
Since the company received emergency authorisation in February, 14.6 million people in the US have received its one-shot vaccine. On Friday, an FDA advisory committee recommended the agency authorise Pfizer-BioNTech booster shots for recipients of the vaccine who are at least 65 or at high risk of COVID. That vaccine, like Modernaʼs, offers high levels of initial protection after two doses, which then seem to diminish slightly over several months.
By contrast, J&Jʼs vaccine has shown little sign of waning. Researchers released a study last week comparing 390,517 vaccinated people with 1,524,153 unvaccinated ones. Up to five months after vaccination, the effectiveness of the J&J vaccine against hospitalisation remained steady at around 81%.
The new clinical trial, which recruited 32,000 volunteers worldwide, compared people who received one dose J&J with those who received two doses eight weeks apart. Results showed that the second boosted antibodies in the blood of volunteers four times as high as the level produced by the first shot. That improvement translated into stronger protection.
In a separate study announced last month, J&J gave boosters to clinical trial volunteers six months after their first dose, and then measured their antibody levels. Initially, the researchers reported that the antibodies rose nine times as high as after the first dose. But in this week’s announcement, the company said the level had continued to rise, reaching 12 times as high as the initial levels.
Some preliminary studies suggest that higher levels of antibodies against the coronavirus produce higher levels of protection against COVID. If thatʼs true, then a second J&J shot given after a wait of several months may prove even more effective than after just eight weeks.
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