The coronavirus vaccines manufactured by Moderna and Pfizer-BioNTech have been shown to be extremely effective in preventing symptomatic and asymptomatic infections in real-life conditions, federal health researchers reported Monday.
Consistent with clinical trial data, a two-dose regimen prevented 90 percent of infections two weeks after the second shot. One dose prevented 80 percent of infections two weeks after vaccination.
The news arrives despite the nation’s rapidly expanding eligibility for vaccines and the average number of daily shots continuing to rise. The seven-day average of vaccines administered hit 2.76 million on Monday, an increase from the previous week’s pace, according to the Centers for Disease Control and Prevention.
But the virus could regain momentum. According to a New York Times database, the seven-day average of new virus cases on Sunday was 63,000, an increase of more than 16 percent over the past two weeks.
Similar increases in summer and winter resulted in a sharp spike in the spread of disease, said Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, at a press conference on Monday. She said she felt an “impending doom” over a possible fourth surge in the virus.
The nation has “so much to hope for,” she said. “But right now I’m scared.”
Scientists have debated whether people who have been vaccinated can still get asymptomatic infections and spread the virus to others. The new study by researchers at the CDC suggested that transmission was likely rare too, given that infections were so rare.
There were also concerns that variants could affect the effectiveness of the vaccines. The results of the study do not confirm this fear. During the time of the study – December 14, 2020 to March 13, 2021 – worrying variants were floating around, but the vaccines still offered strong protection.
The CDC attended 3,950 people who were at high risk of exposure to the virus because they were healthcare workers, first responders, or others on the front lines. Nobody had been infected before.
Most of the participants – 62.8 percent – received both vaccine shots during the study period, and 12.1 percent had one shot. They collected their own nasal swabs each week, which were sent to a central location for PCR testing, the most accurate type of test. The weekly smears allowed the researchers to identify both asymptomatic and symptomatic infections.
The investigators asked the participants about symptoms related to infections such as fever, chills, cough, shortness of breath, sore throat, diarrhea, muscle pain, or loss of smell or taste. They also analyzed patients’ medical records to identify any disease.
Fifty-eight percent of infections were discovered before people had symptoms. Only 10.2 percent of those infected never developed symptoms.
Among those who were fully vaccinated, there were 0.04 infections per 1,000 person-days, which means that out of 1,000 people there would be 0.04 infections per day.
There were 0.19 infections per 1,000 person-days among those who received a dose of the vaccine. In contrast, in unvaccinated people there were 1.38 infections per 1,000 person-days.
Dr. Walensky urged Americans to continue to take precautionary measures and not waste time getting the shots once they are legitimate.
“I ask you to wait just a little longer to get vaccinated if you can so that all of the people we all love will stay here when this pandemic ends,” she said.