Some states in India have been urging the central government to consider a third booster dose for healthcare and frontline workers, but the union health ministry has so far not taken any decision on it, citing the WHO's recommendations against a booster shot
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NEW DELHI: A booster dose of vaccine is more effective in reducing severe covid-19-related outcomes in individuals compared to two shots received at least five months ago, as per a study published in The Lancet.
The study, conducted in Israel, claims to provide the largest peer-reviewed evaluation of the effectiveness of a third “booster" dose of a covid-19 vaccine in a nationwide mass-vaccination setting. The Clalit Research Institute, in collaboration with researchers from Harvard University, analysed integrated health record databases to examine the effectiveness of the third dose of the Pfizer vaccine against the Delta variant of SARS-CoV-2.
The study took place from 30 July through 23 September. Researchers reviewed data from 728,321 individuals aged 12 or above who had received the third dose of the Pfizer vaccine. These individuals were carefully matched 1:1 with 7,28,321 individuals who had received only two shots of the BNT162b2 vaccine at least five months prior.
The matching was based on an extensive set of demographic, geographic and health-related attributes associated with risk of infection, risk of severe disease, health status and health-seeking behaviour. Individuals were assigned to each group dynamically based on their changing vaccination status (1,98,476 individuals moved from the unvaccinated cohort into the vaccinated cohort during the study).
Multiple analyses were conducted to ensure that the estimated vaccine effectiveness was robust to potential biases.
The results, researchers said, show that, compared with individuals who received only two doses five months prior, to those who received three doses of the vaccine (7 days or more after the third dose) had 93% lower risk of covid-19-related hospitalization, 92% lower risk of severe covid-19 disease, and 81% lower risk of covid-19-related death. Vaccine effectiveness was found to be similar for different sexes, age groups (ages 40-69 and 70+) and number of comorbidities, the research showed.
The researchers have indicated that several countries are currently experiencing a resurgence of SARS-CoV-2 infections despite hitherto successful vaccination campaigns, may be due to the greater infectiousness of the delta (B.1.617.2) variant of SARS-CoV-2, and to waning immunity of vaccines administered months earlier.
The study also included a population-level analysis which found that infection rates began to drop for each age group 7-10 days after that age group became eligible for the third dose. The research was conducted by Dr Noam Barda, Dr. Noa Dagan, Professor Cyrille Cohen, and Professor Ran Balicer from the Clalit Research Institute, as well as Professor Miguel Hernán and Professor Marc Lipsitch of the Harvard T.H. Chan School of Public Health, Professor Isaac S. Kohane of Harvard Medical School, and Professor Ben Reis of Boston Children’s Hospital and Harvard Medical School.
"These results show convincingly that the third dose of the vaccine is highly effective against severe covid-19-related outcomes in different age groups and population subgroups, one week after the third dose. These data should facilitate informed policy decision-making," said Ran Balicer, senior author of the study, Director of the Clalit Research Institute and Chief Innovation Officer for Clalit.
The research was funded in part by the newly announced Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.
Some states in India have been urging the central government to consider a third booster dose for healthcare and frontline workers, but the union health ministry has so far not taken any decision on it, citing the World Health Organization’s (WHO) recommendations.
India has so far administered 106 crore vaccine doses. Over the past 24 hours, the country recorded 12,514 fresh infections pushing the active caseload to 1,58,817 - the lowest in 248 days. The weekly positivity rate is at 1.17% and has remained below 2% for the last 38 days now. The daily positivity rate is at 1.42%.
Union health minister Mansukh Mandaviya on Twitter said, “India has administered 1st #COVID19 vaccine dose to 78% of the eligible population and 2nd dose to 35% of the eligible people. Congratulations to all as we rapidly progress on our path to defeat the virus!"
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