How effective is one vaccine dose against Indian variant?

Taking only one dose of a coronavirus vaccine provides much less protection against the new Indian variant of Covid-19 than two, research has shown.

Both the Pfizer and Oxford/AstraZeneca jabs were found to give nearly as effective protection against the variant of the virus first discovered in India, designated B.1.617.2, as against the B.1.1.7 variation first detected in Kent, which remains the dominant strain across the UK.

The study, published by Public Health England (PHE) on 22 May, emphasised the need for two doses.

Through analysing the health data from 1,054 people of different ages and ethnicities between April and May, the study found the Pfizer vaccine was 88 per cent effective about the India variant two weeks after the second dose, while being 93 per cent effective against the Kent variant after the same interval.

The strain first identified in India is more transmissible than the one found in Kent, but there is so far no evidence to suggest it causes a more serious version of the disease.

Two doses of the AstraZeneca vaccine were 60 per cent effective against the India variant and 66 per cent effective against the Kent variant.

However, the study found one dose did not provide as much protection.

Three weeks after the first dose was administered, both vaccines provided only 33 per cent effective against the India variant and 50 per cent effective against the Kent variant.

The study concluded: “After two doses of either vaccine there were only modest differences in vaccine effectiveness with the B.1.617.2 variant. Absolute differences in vaccine effectiveness were more marked with dose one.

“This would support maximizing vaccine uptake with two doses among vulnerable groups.”

Christina Pagel, director of the Clinical Operational Research Unit at University College London and a member of the Independent Scientific Advisory Group for Emergencies, urged the government not to proceed with the next stage of its roadmap out of lockdown before more people have been fully vaccinated with two doses.

“The good news is that it confirms that full vaccination still provides a way out (alongside other measures). The bad news is that it makes proceeding with [the] current roadmap a very bad idea and moving to step three last Monday [17 May] might have been a big mistake,” Ms Pagel said.

“The way out is to vaccinate – fully vaccinate – as many people as possible as quickly as possible. And to do this before we move to step four of the roadmap.”

Paul Hunter, professor of medicine at the University of East Anglia, said: “What is clear from this research is that the main thing we can do to reduce the spread of this variant is to ensure that we get our second dose of vaccine, whatever vaccine we had for our first injection.”

Adam Finn, professor of paediatrics at the University of Bristol, said given the findings public health authorities should focus on “timely administration of second doses ... which ought to provide rapid valuable additional protection against this new strain.”

Ms Pagel said full vaccination should be augmented with support for isolation, local contact tracing, targeted testing, and safer indoor spaces. She said this particularly applied to schools and called on Public Health England to release data on the spread of B.1.617.2 in schools, amid accusations the government had suppressed these data.