Wednesday, showing that it provided participants in a clinical trial with at least some immunity after one dose., offer only hints to a tantalizing question: Could the vaccine, given as a single shot, perform as well as the vaccines that U.S. regulators have already authorized, which are given as two?s, measured in a unit called a geometric mean titer, of 224 to 354, on day 29 after their first vaccine dose; those levels reached 288 to 488 by day 57.
A third authorized vaccine — and one that could be given in a single dose — could help reshape the fight against the Covid-19 pandemic, even if supplies are expected to be limited for some time. A previous version of the paper published in NEJM was released in September on a preprint server, meaning it had not been peer-reviewed. But there are new data on the safety and durability of the vaccine in the current paper, which includes information on the safety of the shot, the duration of immune responses, and the effect of adding a second dose to the first.
Johan Van Hoof, the global head of J&J's vaccine division, said that both animal data, which had shown strong protection based on a single dose, and data made available on Wednesday, had given J&J confidence to attempt a one-dose trial. But part of the reason, he said, was the need for a one-dose vaccine in a pandemic.