A single dose of Pfizer and Moderna covid-19 vaccines is 80% effective in preventing contagion. By supplying the two recommended doses, the effectiveness rises up to 90%. These data come from a study published this Monday by the Centers for Disease Control and Prevention (CDC, in English) of the United States.
Every week, and regardless of whether they showed symptoms or were asymptomatic, routine tests were performed to detect SARS-CoV-2 infections among the volunteers.
“I am excited to share information about this new study. […] that assesses the effectiveness of Pfizer and Moderna vaccines in preventing infections, ”announced the CDC director, Rochelle Wallensky, at a press conference.
The effect has been observed two weeks after the administration of the first dose to the participants in the study, carried out in 3,950 health workers between December 14 and March 13. Every week, and regardless of whether they showed symptoms or were asymptomatic, routine tests were performed to detect SARS-CoV-2 infections among the volunteers.
Lower incidence rate in those vaccinated
Of all the volunteers, who must have had no history of COVID-19 infections, 62.8% (2,479) received the two recommended doses and 477 (12.1%) only one dose of the vaccine. The rest of the participants were not vaccinated.
In those who did not receive any vaccine, an incidence rate of 1.38 infections per 1,000 volunteers was recorded, while those who did receive total or partial vaccination only had incidence rates of 0.04 and 0.19 infections. per 1,000 people, respectively.
According to the Centers for Disease Control and Prevention, these findings indicate that licensed mRNA vaccines are effective in preventing SARS-CoV-2 infection.
They were notified 8 infections confirmed by PCR among those partially immunized (one dose) and 3 other infections among those vaccinated with the full regimen. For the authors, these findings indicate that licensed mRNA vaccines are effective in preventing infection by SARS-CoV-2, regardless of the status of symptoms.
“These provisional results […] demonstrate that current vaccination efforts translate into substantial preventive benefits among working-age adults. They reinforce the CDC’s recommendation for a full two-dose immunization with mRNA vaccines. The covid-19 vaccine is recommended for all candidates”, Concludes the study.
Thompson MG et al. “Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers.” MMWR Morb Mortal Wkly Rep. (2021)
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