The Pfizer and Moderna vaccines have demonstrated an efficacy of 90% against a coronavirus infection (without distinction on the development or not of symptoms) underlines a study conducted in real conditions with just under 4,000 American caregivers.
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In other encouraging news, a partial vaccination with a single dose of one of these two vaccines allowed 80% protection two weeks after the injection, says this study published on Monday.
Conducted by the U.S. Centers for Disease Prevention and Control (CDC), the study looked at the effectiveness of these two messenger RNA vaccines in 3,950 participants across six U.S. states, between Dec. 14 2020 and March 12, 2021.
“This study shows that our national immunization efforts are working,” said CDC director Rochelle Walensky.
“Authorized COVID-19 messenger RNA vaccines provide rapid and important protection in the real world,” she argued.
One of the great strengths of the study was that the participants performed a weekly nasal swab test themselves, which was then analyzed in the laboratory, whether or not they developed symptoms of COVID-19.
These findings add to the growing body of evidence that vaccines do not just stop the development of symptoms of the disease, but also an infection itself, thus being an important tool in preventing the spread of the virus.
Study participants included doctors, nurses, first aid workers and other caregivers from across the country.
Of these, 2,479 (62.8%) received the recommended two doses of the messenger RNA vaccine, and 477 (12.1%) received only one dose.
Three positive cases were identified among those who received the two doses, thus translating an incidence rate of 0.04 per 1000 person-days (a measure of working time), against a rate of 0.19 for those having received a single dose, and 1.38 for those who received no dose.
After adjusting the data for location, vaccine efficacy was estimated to be 80% for one dose, and 90% for two doses.
The study authors stressed, however, that they could not differentiate the estimates between the two vaccines studied, due to the limited number of infections.
The study is still ongoing, and scientists will analyze the sequencing of the virus in cases where it has successfully infected vaccinated people, in order to better understand the reasons behind such contaminations.