The Hindu Explains | Why was the interval between Covishield jabs increased?

The story so far: The Union Health Ministry, based on a recommendation from the National Technical Advisory Group on Immunization (NTAGI), and followed up with a push from the National Expert Group on Vaccine Administration for COVID-19 (NEGVAC), decided to increase the interval between two doses of the Covishield vaccine , manufactured by the Serum Institute of India (SII), to eight weeks, from the earlier six-weeks (maximum) specification. The Centre wrote to all States urging them to follow the new interval span.

Why was the interval increased?

Therapeutics or vaccination for COVID-19 appears to be a work in progress, with new information emerging periodically. The Indian

Covishield is AstraZeneca’s AZD1222 vaccine developed in collaboration with the University of Oxford. In February, data from three single-blind randomised control trials was published in

The Lancet . In participants who received two standard doses, after the second dose, efficacy was higher in those with

a longer interval between the first dose and second dose (at 12 or more weeks) than in those who had a shorter interval (under six weeks). This was bolstered by immunogenicity data that showed antibody-binding responses were over two-fold higher after an interval of 12 or more weeks, compared with an interval of less than 6 weeks in the 18-55 age group.

Also read | Improving Covishield efficiency

This prompted the UK Medicines and Healthcare Products Regulatory Agency to suggest a broad interval of 4-12 weeks, while the WHO’s recommendation is for 8-12 weeks. The increased spacing would also allow more people access to a single dose of the vaccine, giving them some measure of protection against COVID-19. In countries that have problems regarding supply of adequate doses of vaccines, this study seemed to impel decisions to increase the interval.

NTAGI and NEGVAC reportedly considered this data, apart from SII’s bridging study for Covishield in India. The data showed an enhanced efficacy when the interval was increased up to 8 weeks, but no specific benefit was derived after 8 weeks.

What have States done?

States have increased the interval between the prime and booster dose to eight weeks, while allowing people to get the second shot anywhere between the fourth week and the eighth. This pertains only to Covishield, which was given emergency use approval by the Drugs Controller General of India (DCGI) in January. According to government data, Covishield has been the preferred vaccine so far against Bharat Biotech’s Covaxin.

What benefit does this confer?

With the number of cases increasing steadily, the new spacing policy will allow more people to take at least one dose of the vaccine. While it is believed that India is unlikely to face a scarcity of vaccines with two indigenous manufacturers and a temporary brake on the export of Covishied jabs as a precaution, experts reason that the rising graph nevertheless makes it imperative that more people receive at least one dose of the vaccine sooner and have some protection against infection. On the other hand, experts critique the move, believing it might lead to a rash of infections before people get the second dose since the first dose only offers partial protection.