Skip Navigation

Pfizer says experimental COVID-19 vaccine is more than 90% effective

This is the first COVID-19 vaccine in development to have data showing that it exceeded that mark.

  • By Joe Palca/NPR
In this photo from Monday, Jan. 31, 2011, the Pfizer logo is displayed at the drug company's world headquarters in New York. Pfizer Inc. said Tuesday, Feb. 1, its fourth-quarter profit nearly quadrupled from a year ago when it was weighed down by charges as revenue rose 6 percent, thanks to the addition of products from fellow drugmaker Wyeth, acquired late in 2009.

 Mark Lennihan / AP Photo

In this photo from Monday, Jan. 31, 2011, the Pfizer logo is displayed at the drug company's world headquarters in New York. Pfizer Inc. said Tuesday, Feb. 1, its fourth-quarter profit nearly quadrupled from a year ago when it was weighed down by charges as revenue rose 6 percent, thanks to the addition of products from fellow drugmaker Wyeth, acquired late in 2009.

(Washington) — Pfizer’s experimental COVID-19 vaccine appears to be working. The vaccine was found to be more than 90% effective, according to clinical results released by the company Monday.

That news comes from an interim analysis of a study involving 43,538 volunteers, 42% of whom had “diverse backgrounds.”

Each participant got two injections spaced 21 days apart. The analysis compared the number of cases of COVID-19 among the volunteers getting the vaccine, with an approximately equal sized group of volunteers who got an injection of a liquid that didn’t contain the vaccine.

In a news release from Pfizer and its partner BioNTech, the company said results from 94 evaluable cases of COVID-19 among study participants indicated the vaccine is more than 90% effective in preventing COVID-19. The Food and Drug Administration set a minimum effectiveness bar at 50%.

University of Maryland School of Medicine via AP

The first patient enrolled in Pfizer’s COVID-19 coronavirus vaccine clinical trial at the University of Maryland School of Medicine in Baltimore, receives an injection in May. Pfizer’s candidate for a coronavirus vaccine is one of number that are in various stages of development around the world.

This is the first COVID-19 vaccine in development to have data showing that it exceeded that mark.

While promising, this analysis alone does not provide enough information about the vaccine for Pfizer to ask the FDA for permission to distribute it.

The agency has informed manufacturers that it wants a minimum of two months of follow-up data from at least half of the volunteers. The FDA says the reason for that requirement is that most dangerous side effects from a vaccine occur within two months of getting the final injection. Pfizer says that data won’t be available until the third week in November.

The company didn’t say how serious the COVID-19 cases were that occurred in the study, or whether any of them required hospitalization.

The Pfizer vaccine trial is what’s known as an event-driven study. It does not last for a specified period of time. Instead, the study will continue and won’t be considered complete until it has recorded a total of 164 cases of COVID-19 among all the volunteers.

As described in its publicly released protocol, the company had planned to conduct four interim analyses, when a proscribed number of COVID-19 cases had occurred. The results released Monday are from the second one, the company having agreed with the FDA to forgo the first analysis.

Support for WITF is provided by:

Become a WITF sponsor today »

Support for WITF is provided by:

Become a WITF sponsor today »

Up Next
Health

COVID-19 cases top 50 million globally, U.S. nears 10 million