An additional J. & J. injection significantly increases protection against Covid, the company reports.


A second dose of Johnson & Johnson vaccine significantly increased protection against Covid-19, company says announced Tuesday morning.

In a clinical trial, researchers found that two doses of the vaccine provided 94 percent efficacy against mild to severe Covid-19 in the United States, an increase from 74 percent granted with a single shot, the company reported. And two shots showed 100 percent efficacy against serious disease, although that estimate had a wide range of uncertainty.

The data, presented in a press release, has been filed with the Food and Drug Administration, Johnson & Johnson said. Since the company received an emergency clearance in February, 14.6 million people in the United States have received the one-time vaccine.

On Friday, an FDA advisory committee recommended that the agency authorize Pfizer-BioNTech booster shots for vaccine recipients who are at least 65 or at high risk for Covid. That vaccine, like Moderna’s, provides a high degree of initial protection after two doses, which then seem to wane slightly over the course of several months.

In contrast, the Johnson & Johnson vaccine shows little sign of decline. Researchers released a study last week, 390,517 vaccinated people were compared with 1,524,153 unvaccinated people. Up to five months after vaccination, the effectiveness of the Johnson & Johnson vaccine against hospitalization remained stable at around 81 percent.

As the pandemic has unfolded, people who have received the Johnson & Johnson vaccine have: waited for guidance about whether they need a booster. The new clinical study, which recruited 32,000 volunteers around the world, compared people who received one dose of Johnson & Johnson with those who received two doses eight weeks apart.

The researchers found that the second shot increased the level of antibodies in the blood of volunteers four times as much as the level produced by the first shot. That improvement translated into stronger protection.

Many people got their Johnson & Johnson shot much more than eight weeks ago. Other research suggests that the extra time between doses could mean even better protection.

In a separate study announced last month, Johnson & Johnson gave volunteers from clinical trials six months after their first dose of boosters 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 Tuesday’s press release, the company announced that the level had continued to rise and was 12 times higher than its original level.

Some preliminary studies introduce that higher levels of antibodies to the coronavirus provide higher levels of protection against Covid. If that’s true, a second injection of Johnson & Johnson given after a wait of several months may prove even more effective than after just eight weeks.

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