The UK's chief scientific adviser denied that delays to the second dose of the COVID-19 vaccine would make the pandemic worse, saying that suppressing the current spread of the virus was more important than mitigating against a break-out "mutant" strain which was immune to vaccines. 

Patrick Vallance, speaking at a government press briefing, Friday, was responding to UK government research that there is an unquantifiable, but likely small, probability that the delayed second dose could increase the risk of generating a vaccine-resistant COVID-19 mutation.

"There's always some risk if you start to have partial immunity [following the first dose of vaccine]. There's also a benefit, which is part of the immunity can actually stop the infection quicker," said Vallance. 

He added that the research was "appropriately cautious" but "but I don't think it's the biggest risk at all."

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Britain is prioritizing giving first doses of COVID-19 vaccine, allowing up to 12 weeks before a second dose, to give the maximum number of people some initial protection.

Pfizer and BioNTech have warned they have no evidence their vaccine would continue to be protective if the second dose is given more than 21 days after the first.

At the same press conference, Chief Medical Officer for England, Chris Whitty said that "our overall view is that the balance of risk was firmly in favor, at this stage of the epidemic in the UK, of having many more people vaccinated. But that does mean the delay."

The research on COVID-19 "immunity-escape variants" was done for the UK government's New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG).

The report says that "in the short-term, delaying the second dose would be expected to somewhat increase the probability of emergence of vaccine resistance - but probably from a low base."

"Is such an increase material? It is not currently possible to quantify the probability of emergence of vaccine resistance as a result of the delayed second dose, but it is likely to be small."
 

British doctors add to pressure 
 

On Saturday, The British Medical Association (BMA), which represents doctors in the UK, stated they had written to Whitty, urging him to cut the gap between doses from 12 weeks to six.  

The BMA said it supports giving a second dose up to 42 days after the first dose, but that a longer gap is not in line with World Health Organization guidance. It therefore urged Whitty to "urgently review the UK's current position of second doses after 12 weeks."

"The UK's strategy has become increasingly isolated from many other countries," the BMA said.

"BMA members are also concerned that, given the unpredictability of supplies, there may not be any guarantees that second doses of the Pfizer vaccine will be available in 12 weeks' time."

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Whitty said that the longer gap between doses was a "public health decision" aimed at vaccinating many more people and based on a belief that the great majority of protection comes from the first jab.

Britain is using two vaccines, one from Pfizer and the other from AstraZeneca.

AstraZeneca has supported the gap between its jabs, saying data showed an 8-12 week gap was a "sweet spot" for efficacy.

Some 5.38 million people have so far been given a first dose of vaccine in the UK, government data showed.