Pfizer vaccine effective against Delta variant of COVID-19 only after 2 doses: NEJM

The B.1.617.2 (delta) variant is the deadly variant that was the main cause behind the huge second wave in India. This wave affected millions of Indians and has now been detected across the globe, including an increase in cases in the United Kingdom. However, the actual effectiveness of both Pfizer (BNT162b2) and AstraZeneca (ChAdOx1 nCoV-19) vaccines against this variant have been under-documented.

A study was conducted by a group of researchers from the United Kingdom to investigate the effectiveness of both the Pfizer (BNT162b2) and AstraZeneca (ChAdOx1 nCoV-19) vaccines against this delta a variant of COVID-19.

The researchers utilized a test-negative case-control design to predict the efficacy of vaccination against symptomatic disease due to the delta variant or the predominant strain (B.1.1.7, or alpha variant) over the period that the delta variant began circulating.

Both the variants were recognized using the sequencing and based on the spike (S) gene status. Data on all symptomatic sequenced cases of Covid-19 in England were used to estimate the proportion of cases with either variant according to the patients' vaccination status.

The results of the study are as follows:

· Vaccine efficacy after one dose of both; Pfizer (BNT162b2) and AstraZeneca (ChAdOx1 nCoV-19) were relatively lower among persons with the delta variant than among those with the alpha variant.

· With the Pfizer vaccine, the effectiveness was marginally higher than Covidshield after both doses against both the variants; Pfizer efficacy against alpha variant was 93.7% and 88.0% among those with the Delta variant. While Covidshield efficacy after two doses was 74.5% with the alpha variant and 67.0% among those with the Delta variant.

The researchers concluded that only minor differences in vaccine effectiveness were noted with the delta variant as compared with the alpha variant after receiving two vaccine doses. While absolute differences in vaccine effectiveness were more pronounced after receiving a single dose. Thus, this finding would bolster efforts to maximize vaccine uptake with two doses among the at-risk populations.

Reference:

Effectiveness of Covid-19 Vaccines against the B.1.617.2 (Delta) Variant by Bernal J et. al published in The New England Journal of Medicine.

DOI: 10.1056/NEJMoa2108891