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Vaccine Efficacy Against Delta Variant

 Pfizer Vaccine Efficacy Against the Delta and Other Variants

    The Delta Variant, or variant B.1.617.2 was first identified in India in late 2020. This COVID-19 variant has since spread to many other areas including Africa, the United Kingdom, and the United States. The Delta variant is estimated to be more infectious and about 60% more transmissible than the Alpha, or B.1.1.7 variant. Despite its rapid spread, scientists hope to lower the variant's impact through vaccination. However, there has been much discussion as to whether or not the vaccines are as effective, or effective at all, against the Delta variant. A study published in Nature in June 2021 analyzed the effectiveness of the Pfizer vaccine against multiple COVID-19 variants including B.1.617.2. As of June 28, 2021, 81 million Americans have been fully vaccinated with the Pfizer vaccine which has a 95% efficacy against the coronavirus and is available for ages 12 and up. The efficacy data is taken from Pfizer's Phase 3 clinical trial results, which were released in November 2020 and do not include data containing the Delta variant. 

About the Study

    The study utilized sera, or blood components, from 20 individuals drawn 2 or 4 weeks after a second dose of the Pfizer vaccine. The samples were then used to test for neutralizing antibody responses against the SARS-CoV-2 wild-type virus and its spike protein variants B.1.617.1, B.1.617.2, B.1.618 and B.1.525. Both B.1.617.1 and B.1.617.2 emerged from the same variant. All the studied variants were first identified in India except for B.1.525, which was first identified in Nigeria. All these variants are currently circulating in the US.

Study Results

    All sera neutralized the variant viruses at titers above the limit of detection (40). The mean neutralizing titers, or concentration of antibodies, against the wild-type, B.1.617.1, B.1.617.2, B.1.618 and B.1.525 viruses were 502, 320, 157, 355, 343, and 331 respectively. According to the study, the neutralization, or ability of antibodies to bind to the virus, of all variants except B.1.617.1 "was only modestly reduced relative to the neutralization of WT [wild-type] virus." The effectiveness of the vaccine against B.1.617.1 was reduced to 0.31 times that of the wild-type virus.

Other Data and Implications

    The results from the Nature study found only a modest reduction in the efficacy of the Pfizer vaccine against the Delta variant. These results are consistent with a study conducted in the UK, which found that the efficacy of two doses of the Pfizer vaccine against the Delta variant was only modestly reduced to 87.9%. According to a study published in the New England Journal of Medicine, the Pfizer vaccine is 89.5% effective against the B.1.1.7 variant and 75% effective against B.1.351, a variant that initially emerged in South Africa.

    Although the efficacy of the Moderna and Johnson & Johnson vaccines against the Delta variant are still being investigated, study results suggest that the Pfizer vaccine is still effective against the newly emerging COVID-19 variants including the Delta variant. Therefore, getting vaccinated remains key to slowing the spread of the virus and emergence of new variants, as well as putting an end to the pandemic.

Sources

1. Liu, Jianying, et al. “BNT162b2-Elicited Neutralization of B.1.617 and Other SARS-CoV-2 Variants.” Nature, 2021, doi:10.1038/s41586-021-03693-y.

2. Callaway, Ewen. “Delta Coronavirus Variant: Scientists Brace for Impact.” Nature News, Nature Publishing Group, 22 June 2021, www.nature.com/articles/d41586-021-01696-3.

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