The efficacy of the Pfizer/BioNTech vaccine in the prevention of infection with coronavirus has reduced from 88% down to 47% six months after the second dose as Reuters reported citing results of research of Pfizer and Kaiser Permanent scientists.
Scientists have studied electronic medical cards of about 3.4 million people at Kaiser Permanente center in Southern California from December 2020 until August 2021.
The efficacy of the vaccine against Delta strain made 93% after the first months and reduced up to 53% in four months. The efficacy dropped from 97% up to 67% for other Covid variants.
However, the analysis showed that the efficacy of the vaccine in the prevention of hospitalization and death remained high – 90% during at least six months, event against Delta strain. The data suppose that the drop is tied with the decreasing of the efficacy, not more contagious variants of the virus.
This data was considered by the health agencies of the US during the making of decisions on booster doses.
Nevertheless, the results of the study were restricted with the absence of data of observation of main principles of mask regime and professions and it could influence the frequency of testing and possibility of contact with the virus.
As we reported, a large study carried out by the US Centres for Disease Control and Prevention shows that the efficacy of mRNA vaccines drops from 91% to 66% against the Delta variant.