Pfizer vaccine, efficacy against infection drops to 47% after 6 months

The efficacy of the Pfizer vaccine against covid decreased over 6 months, from 88% recorded one month after the two doses to 47% after 6 months. However, vaccine efficacy against admissions for all variants, including Delta, remained high (90%) for at least 6 months. This is the data that emerges from a study by the Kaiser Permanente consortium and Pfizer, published in ‘The Lancet’. In a specific analysis, the researchers found that these reductions in efficacy against infections over time are likely due to the decline in the shield effect, not the Delta variant escaping vaccine protection. Read also These results, the experts conclude, underline “the importance of increasing vaccination rates worldwide and of monitoring vaccine efficacy over time to determine which populations should be prioritized for boosters”. The results communicated by the authors of the work are consistent with the preliminary reports of the US Centers for Disease Control and Prevention (CDC) and the Israeli Ministry of Health, which found reductions in protection from infection after about 6 months. “Our study confirms that vaccines are a vital tool for controlling the pandemic and remain highly effective in preventing serious illness and hospitalization, including from Delta and other variants of concern – says lead author, Sara Tartof, of the Department of Research and Evaluation of the Kaiser Permanente of Southern California – Protection against infection decreases in the months following a second dose. Although this study provides evidence that immunity decreases for all age groups that received the vaccine, the CDC’s Advisory Committee on Immunization practices required further research to determine whether the recall it should be made available to all age groups eligible for this vaccine “.” In line with recent FDA and CDC recommendations – continues Tartof – the “third dose” considerations should take into account the global supply of Covid vaccines, as people in many countries around the world have not yet received primary vaccinations. “Researchers analyzed 3.4 million electronic health records from the Kaiser Permanente Southern California (KPSC) health system between December 4, 2020 and August 8, 2021 , to evaluate the efficacy of the Pfizer / BioNTech vaccine against Sars-CoV-2 infections and Covid-related hospitalization. During the study period, 5.4% of people were infected. Of the infected, 6.6% were hospitalized. On average this happened between 3 and 4 months after the subject had been fully vaccinated. Specifically for the Delta variant, the percentage of positive cases attributed to the mutant increased from 0.6% in April 2021 to almost 50% in April 2021. 87% by July 2021, confirming that Delta had become dominant in the United States. The vaccine efficacy against Delta infections one month after two doses was 93% and dropped to 53% after 5 months. Efficacy against other (non-Delta) variants one month later was 97% and dropped to 67% after 4 months. Efficacy against Delta-related hospitalizations remained high (93%) for the duration of the study period.