Johnson & Johnson cuts size of Covid-19 vaccine study due to prevalence of disease in U.S.

Johnson & Johnson is cutting the size of its pivotal U.S. Covid-19 vaccine trial — the only major study testing a single dose of a Covid vaccine — from 60,000 volunteers to 40,000 volunteers.

The change is being made possible by the fact that Covid-19 is so pervasive across the country, according to a person familiar with the matter. The more virus there is in the U.S., the more likely it is that participants will be exposed to it, meaning researchers will be able to reach conclusions based on a smaller trial.

Changing the size of the study does not indicate that results will come on a different timetable, or anything about whether they will be positive or negative.

During a press briefing on Wednesday, Moncef Slaoui, the head of Operation Warp Speed, made brief mention of the change.

“We have already recruited more than 38,000 subjects in the study,” Slaoui said. “With J&J, we decided to cap the recruitment to around 40,000 subjects, which will happen by the end of this week, so in the next two [or] three days.”

In a statement, J&J said: “We continue to anticipate that interim data from the ENSEMBLE trial will be available by the end of January. If the vaccine is safe and effective, an emergency use authorization application could be submitted to the FDA in February.”

The J&J study, started Sept. 23, was the largest Phase 3 trial of a Covid-19 vaccine. The vaccine J&J has developed uses an adenoviral vector, a type of genetically modified virus that leads the body to produce a protein to which the immune system then reacts, in theory inoculating the recipient against the virus.

Like other Covid-19 trials, the goal is to follow the volunteers enrolled in the study until 154 of them have contracted the virus that causes the disease. In the case of the J&J study, in order to be counted, a case of Covid-19 must be severe or moderate and occur at least two weeks after vaccination.

Because Covid-19 cases are skyrocketing in the U.S., J&J will reach this milestone while enrolling fewer patients. That leaves the J&J study as about the same size as that run by Pfizer and BioNTech, which included 44,000 volunteers in their study of the first vaccine to deliver positive results, and somewhat bigger than the 30,000-patient study run by Moderna, which developed the second vaccine to show positive results.

Johnson & Johnson is also conducting a second study using two doses of the same vaccine in Europe and the U.S. That study plans to enroll 30,000 volunteers.

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