New Delhi: Even a single dose of both Pfizer and AstraZeneca vaccines provide protection against severe Covid-19 infection, an analysis by the Public Health England (PHE) has found. The study also noted that both vaccines work against the UK variant of the SARS-CoV2 virus (VOC 202012/01).
“Vaccination with a single dose of either vaccine is associated with a significant reduction in symptomatic SARS-CoV2 positive cases in older adults, with even greater protection against severe disease. Both vaccines show similar effects. Protection was maintained for the duration of the follow up (<6 weeks),” PHE doctors from across the UK noted in a pre-print paper.
The paper also said, “A second dose of BNT162B2 provides further protection against symptomatic disease but second doses of ChAdOx1 have not yet been rolled out in England. There is a clear effect of the vaccines against the UK variant of concern.”
BNT162B2 is the Pfizer mRNA vaccine and ChAdOx1 is the AstraZeneca one. While the former is yet to be approved in India, the latter is a part of India’s Covid-19 vaccination programme under the brand name Covisheld.
The study aimed at arriving at a real world estimation of how effective the two vaccines are and covered all adults in England aged 70 years and above — about 7.5 million people. UK was the first country in the world to roll out a vaccination programme against Covid-19 on 8 December 2020. Recent analyses show that the UK variant which first surfaced in Kent is now the dominant strain in the country.
Slight improvement in outcome with second dose
The researchers, in what is the first real world estimate of vaccine effectiveness in the UK, found that while a single dose of the Pfizer vaccine is approximately 60-70 per cent effective in preventing symptomatic disease in adults aged 70 years or more, with two doses that figure touches 85-90 per cent.
“Those vaccinated who went on to become a symptomatic case has a 44 per cent lower risk of hospitalisation and a 51 per cent lower risk of death compared to unvaccinated cases. We also provide the first real world evidence of the effectiveness of the ChAdOx1 vaccine,” the researchers wrote.
“The effect of a single dose of the ChAdOx1 vaccine against symptomatic disease was approximately 60-75 per cent and there was again an additional protective effect against hospitalisation, though it is too early to assess the effect and mortality. VOC 202012/01 now dominates in the UK and these results will largely reflect vaccine effectiveness against this variant,” they further noted.
Mary Ramsay, PHE’s head of immunisation, told The BMJ, “This adds to growing evidence showing that the vaccines are working to reduce infections and save lives. While there remains much more data to follow, this is encouraging, and we are increasingly confident that vaccines are making a real difference.”