Johnson & Johnson said Tuesday a second shot of its COVID-19 vaccine given about two months after the first increased its effectiveness to 94% in the United States against moderate to severe forms of the disease.
That compares to 70% protection with a single dose.
J&J said a booster given two months after the first dose increased antibody levels four to six-fold.
The data will help J&J make its case to U.S. regulators for a booster shot even as the company stresses the durability of its single-shot vaccine as a tool to ease the global pandemic.
The company has now "generated evidence that a booster shot further increases protection against COVID-19," Dr. Paul Stoffels, J&J’s chief scientific officer, said in a statement.
J&J said a booster given two months after the first dose increased antibody levels four to six-fold. When given six months after the first dose, antibody levels shot up twelve-fold, data released last month showed, suggesting a large improvement in protection with the longer interval between doses.
Side effects with two doses were comparable to those seen in studies with the single-dose vaccine.
On Friday, an FDA advisory committee voted to recommend emergency authorization of additional Pfizer shots for Americans 65 and older and those at high risk of severe illness, but voted to recommend against broader approval, saying they want to see more data.
J&J said it has submitted data to the FDA and plans to submit it to other regulators, the World Health Organization and other vaccine advisory groups worldwide to inform their decision-making.
According to evidence from a separate real world study of nearly 400,000 people in the United States who got the J&J shot, the vaccine was 79% effective at preventing COVID-19 infections and 81% effective at preventing hospitalizations compared with 1.52 million people of similar ages, genders and health issues who were unvaccinated.
J&J said there was no evidence of reduced effectiveness over the study's duration from March to late July - a period that included the impact of the Delta variant.
Vaccine effectiveness in the real world study varied by age. For those under age 60, the vaccine was 86% effective at preventing hospitalization versus 78% for those 60 and older.