Pfizer vaccine Covid-19. Photo by Pfizer Canada.
31 Mar 2021

Study on first responders and health care workers shows 80 % effectiveness after just one shot of Covid-19 vaccine


According to a new US study,  COVID-19 vaccines developed by Pfizer with BioNTech and Moderna reduced the risk of infection by 80 per cent after only one shot.

This result was found after two weeks or more after the first out of two injections. After the second injection, the effectiveness increased to 95 %. 

This is according to data from a real-world study of vaccinated U.S. health-care personnel and first responders released on Monday March 29th. 

The study was conducted by the U.S. Centers for Disease Control and Prevention (CDC). They attempted to evaluate the vaccines' ability to protect against infection, including infections that did not cause symptoms.

"This is very reassuring news," said the CDC's Mark Thompson, who leads the study. "We have a vaccine that's working very well."

The study researched the effectiveness of the mRNA vaccines on 3,950 participants in six US states during 13 weeks from December 14, 2020 to March 13, 2021.

Out of the almost 4000 participants, there were 205 infections, with the vast majority (161 cases) in the unvaccinated control group.

Of the 44 cases in the vaccinated group, the CDC said roughly 3/4 (33 cases) were in people who were exposed before the first shot had become fully effective (within two weeks of the first shot).

No one in the study died, and only two were hospitalized. 

"The authorized mRNA COVID-19 vaccines provided early, substantial real-world protection against infection for our nation's health-care personnel, first responders, and other frontline essential workers," CDC Director Rochelle Walensky said in a statement.

About two-thirds of the participants who were vaccinated got Pfizer shots, one-third got Moderna and five got the newest shot from Johnson & Johnson. The study was done in Miami; Duluth, Minnesota; Portland, Oregon; Temple, Texas; Salt Lake City; and Phoenix and other areas in Arizona.