Johnson & Johnson Begins Phase 3 Trial of Covid-19 Vaccine

“The single dose could be sufficient to protect people for a long time,” he said.

A Phase 1 / 2 trial measures immune responses but cannot determine if a vaccine actually protects against a virus. Dr. Barouch noted that a single dose of the vaccine produced a level of antibodies in people that his previous experiments showed was enough to protect monkeys.

The company is planning to recruit up to 60,000 people over the age of 18 for its Phase 3 trial in the United States, Argentina, Brazil, Chile, Colombia, Mexico, Peru and South Africa.

The trial is about twice as big as Moderna’s, and significantly larger than Pfizer’s. This month, Pfizer announced it planned to increase its trial to 44,000 people from 30,000.

Dr. Barouch said the larger size would provide a better sense of the safety of the vaccine and might also reduce the time it takes to determine if the vaccine is effective. “It will provide for a faster readout,” he said.

Johnson & Johnson posted the trial blueprints, known as a protocol, on its website on Wednesday, following the lead of its competitors, which did so after independent researchers called on the companies to be more transparent. The protocol showed that the trial’s goal is to measure whether the vaccine shows 60 percent efficacy after 164 participants develop Covid-19.

An outside review board can begin evaluating the results for efficacy after 20 people have become sick, and then the board will check in at least once a week after that, the protocol stated. Dr. Stoffels said that the trial would not be stopped early unless there is overwhelmingly positive data on safety and effectiveness, and the data include sick people in high-risk populations — such as older people. Pfizer’s plan allowed an outside board to check the data for early efficacy four times, beginning after 32 participants have developed Covid-19. Moderna’s allowed for two early looks, starting after 53 cases.

Johnson & Johnson will be testing the single dose in the 60,000-person trial and also run a smaller trial using a double dose.

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