Pfizer and AstraZeneca Covid-19 vaccines are effective against symptomatic disease due to the B.1.617.2 variant detected in India, according to a new study conducted by Public Health England and reported as a preprint.
The two doses of the Pfizer vaccine showed 87.9% efficacy in preventing symptomatic disease due to the B.1.617.2 variant, while the two doses of the AstraZeneca vaccine demonstrated 59.8% efficacy against the B.1.617.2 variant.
Efficacy against B.1.1.7 (which first emerged in the UK during September 2020) was 93.4% with two doses of Pfizer vaccine as compared to 66% efficacy with two doses of the AstraZeneca vaccine.
However, the effectiveness three weeks after single dose of both vaccines amounted to only 33%.
The effect of vaccination on the B.1.617.2 variant was assessed using the following two approaches:
- First, a test negative case control (TNCC) design was used to estimate vaccine effectiveness against symptomatic disease with the B.1.617.2 variant compared to the B.1.1.7 variant over the same period.
- Second, the proportion of cases with the B.1.617.2 variant relative to the main circulating virus (the B.1.1.7 variant) was estimated by vaccination status.
The B.1.617.2 and B.1.1.7 variants were identified by whole genome sequencing as well as a 3-target PCR assay (samples testing positive or negative on the spike gene target). A total of 12,675 sequenced cases were analysed. Of these, 11.621 were B.1.1.7 variant, while B.1.617.2 was detected in 1054 cases.
The study authors write, “These findings suggest a modest reduction in vaccine effectiveness. Nevertheless, a clear effect of both vaccines was noted with high levels of effectiveness after two doses. Vaccine effects after two doses of ChAdOx1 vaccine were smaller than for BNT162b2 against either variant.”
The B.1.617 has been declared as a variant of concern by the WHO and Public Health England. It has not only become the dominant strain (B.1.617.2) in India, it has rapidly crossed borders and spread to about 40 countries.
Besides increased transmissibility and disease severity, variants of concern interfere with diagnostic test targets, reduce susceptibility to neutralising antibodies and increase resistance to treatment. Another concern is their ability to evade natural or vaccine-induced immunity.
The AstraZeneca vaccine is marketed as Covishield in India.
The results of this study are encouraging and reassure that the vaccines will be effective in reducing severe disease and prevent hospitalization and deaths. This study also reiterates the need for full vaccination, especially for the high risk population groups. It is important that people take both doses of the vaccine to get maximum protection.
Source: Jamie Lopez Bernal, et al. Effectiveness of COVID-19 vaccines against the B.1.617.2 variant.
https://www.medrxiv.org/content/10.1101/2021.05.22.21257658v1, Posted May 24, 2021. doi: https://doi.org/10.1101/2021.05.22.21257658.
Dr. Surya Kant
Professor and HeadDepartment of Respiratory Medicine, KGMU, UP, Lucknow .National Vice Chairman IMA-AMS.