COVID-19: Extending gap between coronavirus jab doses creates small risk of 'escaped mutant' variant - Whitty

·4-min read

The UK's top scientists have defended the decision to delay second vaccine doses - although admitted there is a slightly increased risk of an "escaped mutant" version of the virus emerging.

Both the Oxford/AstraZeneca and the Pfizer/BioNTech vaccines are administered in two doses and should be given in as short a time as possible, but rapidly rising COVID-19 cases in the UK have prompted decision-makers to delay the second dose to within 12 weeks of the first.

This means more people can be given their first dose - and have some amount of protection - in a shorter space of time.

However, some experts have warned spacing out the doses could impact long-term protection and even increase the risk of an "escaped mutant" variant which could be resistant to the vaccines.

Asked in a Downing Street briefing whether delaying second doses could increase the risk of the virus mutating, England's chief medical officer Professor Chris Whitty admitted it was a "real worry but quite a small real worry".

He explained there was a "balance of risk" that decision-makers had to take between getting more people vaccinated more quickly and the risk of further mutations.

"By extending the gap [between doses], we are going to over the next three months essentially double the number of people who can be vaccinated," he said.

Professor Whitty said scientists predict people will be offered "quite a lot more than 50%" protection after a first vaccine dose, which would be enough to keep the pandemic under control.

He said there is a "theoretical risk that it could lead to an increased risk of an escaped mutant", but experts including SAGE and the regulatory body MHRA had agreed the risk was "sufficiently small".

Modellers believe spreading the UK's supplies of the vaccines for three months could save up to 6,000 lives, and experts have said maximising the number of people with partial immunity should reduce the number of severe COVID-19 cases and help the burden on hospitals.

Viruses often adapt themselves to continue spreading, and vaccination can put pressure on the virus to keep evolving - leading to potential mutations.

At the same time, the more a virus is circulating and the more people it infects, the more chance it has to mutate.

The issue has been raised by former World Health Organisation (WHO) director Anthony Costello, who wrote on Twitter: "If we assume that over the next 12 weeks 12-20 million people get one dose of a vaccine and are told or believe it gives 90% protection what % will actually go for a second jab?

"We might assume second dose coverage is at best 70%. That means between 4 and 6.7 million people might have fading protection.

"Will the risk of creating a vaccine resistant mutant in this group of people, which could spread rapidly to 7 billion people around the world, outweigh the benefits of 6000 deaths prevented."

Florian Krammer, a microbiology professor at the Icahn School of Medicine, also tweeted: "If virus circulation is low, the 12 week window might not be a big problem.

"But if virus circulation is sky high (like right now in the UK), it is not a good idea."

WHO has recommended that patients should be given the two doses of the vaccines within 21-28 days, but also acknowledged some countries have had to make more difficult decisions.

"While we acknowledge the absence of data on safety and efficacy after one dose beyond the three-four weeks studied in the clinical trials, SAGE made a provision for countries in exceptional circumstances of [Pfizer] vaccine supply constraints to delay the administration of the second dose for a few weeks in order to maximise the number of individuals benefiting from a first dose," said Alejandro Cravioto, chairman of WHO's Strategic Advisory Group of Experts on Immunization (SAGE).

"I think we have to be a bit open to these types of decisions which countries have to make according to their own epidemiological situations."

Professor Whitty himself suggested the spacing of doses was not ideal, but said the number of vaccine doses available to the UK "constrains" what action can be taken.

In a stark message against a backdrop of rising hospital admissions and deaths, he said: "If we had an infinite amount of vaccine we might have taken a different approach - but we don't."