Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant
India has experienced a surge in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cases with newly detected B.1.617.2 (delta) variant. The effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines against this variant is unknown. Jamie Lopez Bernal and colleagues conducted research under the title “Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant” published in the New England Journal of Medicine. The summary of this study is given below:
Objective:
To investigate the effectiveness of two Covid-19 vaccines, namely BNT162b2 and ChAdOx1 nCoV-19 (AstraZeneca), against symptomatic disease caused by newly emerged delta variant.
Method:
A test-negative case-control design was used to investigate the effectiveness of vaccination against symptomatic disease created by the delta variant or the predominant strain such as alpha variant or B.1.1.7. Variants were recognized with the help of sequencing and on the basis of the spike (S) gene status. Data on all symptomatic sequenced cases of Covid-19 in England were used to evaluate the proportion of cases with either variant according to the patients’ vaccination status.
Findings:
The study reports that both the vaccines have high levels of effectiveness against symptomatic disease with the delta variant after two doses. Vaccine effectiveness against either variant was smaller after receiving two doses of the ChAdOx1 nCoV-19 vaccine as compared to two doses of the BNT162b2 vaccine.
Limitation:
The author acknowledges that the findings are observational and should be applied
with caution. Low sensitivity or specificity of PCR testing might result in misclassification of cases and controls, this might reduce the estimates of vaccine effectiveness.
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