Under real-world conditions, the Pfizer and Moderna Covid-19 vaccines provide highly effective protection, according to a new report from the US Centers for Disease Control and Prevention.
At full vaccination, the vaccines were 90% effective at preventing infections, including infections that had no symptoms. At a single dose, they were 80% protective, according to the agency's Morbidity and Mortality Weekly Report published Monday.
The study looked at how the vaccines protected nearly 4,000 health care workers and first responders. The volunteers in the study worked in eight locations around the country and had been observed from mid-December to mid-March.
The CDC tested volunteers routinely regardless of symptoms. The CDC also monitored the volunteers through text message, e-mails and direct medical reports. The volunteers also did a nasal swab once a week.
Most of the volunteers, more than 62%, had received both doses of either a Pfizer or Moderna Covid-19 vaccine. More than 12% had received just a single dose.
Among the 2,961 people vaccinated with one or more doses and the 989 unvaccinated participants, a total of 205 had a positive PCR test for Covid-19, more than 87% of those cases had symptoms. Nearly 23% of the cases sought help from a doctor. There were two hospitalizations, but no deaths.
The results of this study are similar to what scientists saw in clinical trials for the vaccines, but studies like this are important to show how effective the vaccines are, particularly in a population that, through their work, can encounters a large number of people who have Covid-19.
“Reducing the risk for transmissible infection, which can occur among persons with asymptomatic infection or among persons several days before symptoms onset, is especially important among health care personnel, first responders, and other essential and frontline workers given their potential to transmit the virus through frequent close contact with patients and the public,” the report concluded.