A second dose of the Johnson & Johnson vaccine has significantly increased protection against Covid-19, the company announced on Tuesday morning.
In a clinical study, researchers found that two doses of the vaccine in the US provided 94 percent effectiveness against mild to severe Covid-19, versus 74 percent with a single vaccination, the company reported. And two shots showed 100 percent effectiveness against major diseases, although that estimate had great uncertainty.
The data, which was presented in a press release, has been submitted to the Food and Drug Administration, Johnson & Johnson said. Since the company received an emergency clearance in February, 14.6 million people in the US have received its single vaccine.
On Friday, an FDA advisory committee recommended that the agency approve Pfizer BioNTech booster vaccinations for recipients of the vaccine who are at least 65 years old or at high risk of Covid. This vaccine, like Moderna’s, offers high initial protection after two doses, which then appears to decrease slightly over several months.
In contrast, the Johnson & Johnson vaccine has barely waned. Researchers published a study last week comparing 390,517 people who were vaccinated with 1,524,153 people who were not vaccinated. Up to five months after vaccination, the effectiveness of the Johnson & Johnson vaccine against hospital stays remained constant at around 81 percent.
As the pandemic unfolded, people who received the Johnson & Johnson vaccine have been waiting for guidance on whether to need a booster dose. The new clinical study, which enrolled 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 raised the level of antibodies in the volunteers’ blood four times the level produced by the first shot. This improvement resulted in greater protection.
Many people got their Johnson & Johnson intake well over 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 a booster dose to clinical trial volunteers six months after the 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. However, in Tuesday’s press release, the company announced that levels had continued to rise, reaching 12 times the original level.
Some preliminary studies suggest that higher levels of antibodies against the coronavirus result in greater protection against Covid. If that’s true, a second Johnson & Johnson syringe may prove to be even more effective after waiting several months than after just eight weeks.