The efficacy of Pfizer’s covid vaccine decreased over 6 months, going from 88% recorded one month after the two doses to 47% after 6 months. However thevaccine efficacy against hospitalizations for all variants, including Delta, has been 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.
These results, the experts conclude, underline “theimportance of increasing vaccination rates around the world and to monitor vaccine efficacy over time to determine which populations should be prioritized for boosters. “The findings reported by the authors of the work are consistent with preliminary reports from the US Centers for Control and Prevention of diseases (CDC) and the Israeli Ministry of Health, which found reductions in protection from the infection after about 6 months.
“Our study confirms that vaccines are a key tool in 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 Research Department. and Southern California Kaiser Permanente Assessment – 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 Advisory Committee of the CDs on immunization practices called for further research to determine if the booster should be made available to all age groups eligible for this vaccine. “
“In line with recent FDA and CDC recommendations – continues Tartof – the considerations” in relation to the third dose “should take into account the global supply of Covid vaccines, since people in many countries of the world have not yet received primary vaccinations”.
Researchers analyzed 3.4 million Kaiser Permanente Southern California (KPSC) health system electronic health records between December 4, 2020 and August 8, 2021, to evaluate the efficacy of Pfizer / BioNTech vaccine against SARS infections. CoV-2 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 was fully vaccinated.
As regards specifically the Delta variant, the percentage of positive cases attributed to the mutant increased from 0.6% in April 2021 to nearly 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.