Americans and Europeans who thought they got off easy with just one shot of the Johnson & Johnson COVID-19 vaccine will need a booster to be fully protected, according to data from Phase 2 studies that show those who receive a second J&J jab see a nine-fold increase in antibody response. “New interim data from these studies demonstrate that a booster dose of the Johnson & Johnson COVID-19 vaccine generated a rapid and robust increase in spike-binding antibodies, nine-fold higher than 28 days after the primary single-dose vaccination,” the company said in its statement, adding that a single shot is still effective in generating a strong and robust immune response. “With these new data, we also see that a booster dose of the Johnson & Johnson COVID-19 vaccine further increases antibody responses among study participants who had previously received our vaccine.”