A new study revealed that Covishield, the vaccine against coronavirus, has an 81.3 per cent efficacy if two doses are administered 12 weeks apart.

The study demonstrated that people younger than 55 develop a two-fold antibody response against the virus if the doses were taken 12 weeks apart.

The study, published in the journal Lancet, found that the Covishield’s efficacy was only 55.1 per cent when the two doses were administered less than six weeks apart.

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However, the efficacy rate of Oxford University and AstraZeneca’s coronavirus vaccine developed in India rose considerably when the participants received one standard dose and another low dose as opposed to two standard doses.

The efficacy was 63·1 per cent in those who received two standard doses and 80·7 per cent in those who received the low dose plus the standard dose.


The study stated: “Notably, in exploratory analyses, vaccine efficacy after a single standard dose was 76 per cent from Day 22 to Day 90, and antibody levels were maintained during this period with minimal waning.”

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“Overall, the value of this study is in providing evidence that a single dose of the Covishield vaccine is highly efficacious in the 90 days after vaccination, a longer prime-boost interval results in higher vaccine efficacy, and that protection against symptomatic Covid-19 is maintained despite a longer dosing interval,” the study elaborated.

The study was conducted by Ivan FN Hung from the Department of Medicine, the University of Hong Kong and Queen Mary Hospital, Hong Kong, and Gregory A Poland from Mayo Vaccine Research Group, Mayo Clinic, Rochester, US.