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Pfizer Efficacy Against Delta Variant

Large Scale Study on Pfizer's Effectiveness Against the Delta Variant
    
    With the delta, or B.1.617.2 variant spreading rapidly to over 100 countries and causing a surge of COVID-19 cases, there have been concerns as to whether or not COVID-19 vaccines provide sufficient efficacy against the highly transmissible variant. A previous study analyzed the antibody levels of 20 individuals who were fully vaccinated with Pfizer and later exposed to a SARS-CoV-2 variant. It was found that the delta variant did not significantly reduce antibody levels. While this study served as a good starting point for researching vaccine efficacy against delta, more recent studies utilizing COVID-19 case data and larger sample sizes have come out and produced more detailed conclusions. One of these studies was published on July 21, 2021 in the New England Journal of Medicine and investigated the efficacy of the Pfizer and Moderna vaccine against the delta variant.

About the Study

    The study utilized 19,109 COVID-19 cases from the United Kingdom with data from positive COVID-19 tests taken between October 20, 2020 and May 21, 2021. Only individuals of at least 16 years of age who had a positive COVID-19 test caused by the alpha or delta variant and had been fully vaccinated with Pfizer or AstraZeneca vaccines were included in the study. A test-negative case-control design was used to estimate the effectiveness of the Pfizer and AstraZeneca vaccines against infection caused by the delta variant and the alpha variant, or B.1.1.7, during a time both variants were circulating. Variants were identified using sequencing and the proportion of cases caused by the delta variant was estimated according to vaccination status. 

Study Results

    Of the 19,109 cases, the alpha variant was detected in 14,837 samples, or 77.6% of total cases, and the delta variant was detected in 4,272 samples, or 22.4% of total cases. The effectiveness of one dose of either the Pfizer or AstraZeneca vaccines was notably lower among participants with the delta variant (30.7% effective) than those with the alpha variant (48.7% effective). The difference in vaccine effectiveness between the two variants was smaller among participants who had received two doses of the vaccine. The effectiveness of two doses of the Pfizer vaccine was 93.7% against the alpha variant and 88% against the delta variant. With AstraZeneca, the effectiveness of two doses was 74.5% against the alpha variant and 67% against the delta variant.  While the difference in effectiveness of two doses of the AstraZeneca vaccine was lower than that of the Pfizer vaccine, the difference in effectiveness between the alpha and delta variants was small.

Implications

    While some people have been wondering whether or not it's worthwhile to get vaccinated, this study highlights the value of vaccination with data that the Pfizer and AstraZeneca vaccines are still highly effective against both the delta and alpha variants. Findings of reduced efficacy after the first dose emphasizes the importance of receiving a full two doses of vaccines like Pfizer, AstraZeneca, and Moderna. With the rapid spread of the delta variant, getting fully vaccinated is key to lowering COVID-19 case rates and keeping yourself and others protected.

Sources

1. Lopez Bernal, Jamie, et al. “Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant.” New England Journal of Medicine, 21 July 2021, doi:10.1056/nejmoa2108891.

Comments

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