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Coronavirus vaccines made by Moderna and Pfizer-BioNTech are proving to be very effective in preventing symptomatic and asymptomatic infections under real conditions, federal health researchers reported on Monday.
Consistent with clinical trial data, a two-dose regimen prevented 90 percent of infections two weeks after the second stroke. One dose prevented 80 percent of infections two weeks after vaccination.
There has been a debate over whether people who have been vaccinated can still get asymptomatic infections and pass the virus on to others. The study, conducted by researchers from the Centers for Disease Control and Prevention, suggested that because infections were so rare, transmission is likely also rare.
There are also concerns that the variants may make the vaccines less effective. The results of the study do not confirm this fear. Disturbing variants were circulating during the study period – from December 14, 2020 to March 13, 2021 – but the vaccines still provided potent protection.
The CDC recruited 3,950 people at high risk of being exposed to the virus because they were healthcare workers, first responders or others on the front lines. None had previously been infected with the coronavirus.
Most – 62.8 percent – received both vaccines during the study period, and 12.1 percent received one. The participants had no previous infection with the coronavirus.
Participants 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 samples allowed researchers to detect asymptomatic infections as well as symptomatic infections.
Investigators also asked participants about symptoms associated with the infection, including fever, chills, cough, shortness of breath, sore throat, diarrhea, muscle pain, or loss of smell or taste. . Researchers also analyzed patients’ medical records for illnesses.
Fifty-eight percent of infections were detected before people had symptoms. Only 10.2% of those infected never developed symptoms.
Among those who were fully immunized, there were 0.04 infections per 1,000 person-days, which means that in 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, there were 1.38 infections per 1,000 person-days among unvaccinated people.
“This study shows that our national immunization efforts are working,” CDC director Dr. Rochelle P. Walensky said in a press release.
The CDC said this was the first of many vaccine effectiveness studies it would conduct.
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