A new study published in The Lancet journal has revealed that the protection offered by the Oxford-AstraZeneca Covid-19 vaccine (named Covishield in India), wanes after three months of receiving two doses.
"We found waning vaccine protection of ChAdOx1 nCoV-19 [scientific name of the vaccine] against Covid-19 hospital admissions and deaths in both Scotland and Brazil, this becoming evident within three months of the second vaccine dose," said a team of researchers led by University of Edinburgh.
The findings drawn from data sets in Brazil and Scotland suggested that booster programmes are needed to help maintain protection from severe disease.
"Consideration needs to be given to providing booster vaccine doses for people who have received [the vaccine]."
As per a PTI report, the researchers analysed data for two million people in Scotland and 42 million people in Brazil who had been vaccinated with AstraZeneca.
Researchers were able to compare the Scottish and Brazilian data because a similar interval of three months was used between doses, and because those at highest risk of severe disease and healthcare workers had been prioritised for vaccination in both places.
The decline in effectiveness begins to first appear at around three months, when the risk of hospitalisation and death is double that of two weeks after the second dose, they said.
The researchers found that the risk of hospitalisation and death increases threefold just short of four months after the second vaccine dose. Similar numbers were seen for Brazil, they said.
Professor Aziz Sheikh, from the University of Edinburgh, U.K noted that although vaccines have been a key tool in fighting the pandemic, but waning in their effectiveness has been a concern for a while.
He also said that it should be possible for governments to design booster programmes that can ensure maximum protection is maintained by identifying when waning first starts to occur in the Oxford-AstraZeneca vaccine,
The study also estimated vaccine effectiveness at similar fortnightly intervals by comparing outcomes of people who have been jabbed with those who are unvaccinated.
However, the experts warned that these figures should be treated with caution because it is becoming harder to compare unvaccinated people to those vaccinated with similar characteristics, particularly among older age groups where so many people are now vaccinated.