The Oxford / AstraZeneca COVID-19 vaccine offers better protection the more time left before a second dose, said a government immunization adviser.
Professor Anthony Harnden, vice president of the Joint Vaccination and Immunization Committee (JCVI), said the data supports a second deferred dose of the Oxford vaccine, but that “we are not so sure” about the rival vaccine from Pfizer.
Both vaccines require two doses and experts recommend that the second dose be administered between four and 12 weeks after the first.
But Pfizer said its tests did not examine this delay – its researchers looked at a three-week interval between applications.
Watch: Oxford jab more effective when the second dose is delayed
Prof Harnden told the Commons science and technology committee: “What was really interesting about the data from Oxford / AstraZeneca was that the longer we left the second dose, the better the long-term protection you get from the vaccine.
“Not only was the data from the Oxford / AstraZeneca study really impressive in terms of protection against really serious illnesses, hospitalization and death – in fact, some of the data suggested that it is up to 100% effective in that.
“So we were very confident that this will not only protect serious illnesses, but as a long-term strategy for those individuals who may end up getting better long-term protection with a second deferred dose.
“We are not so sure about that with Pfizer, I have to say we are, but we are much safer about the Oxford / AstraZeneca vaccine.”
Two UK studies released on Monday showed that COVID-19 vaccination programs are contributing to a sharp drop in hospitalizations, raising hopes that vaccines will work as well in the real world as they did in carefully controlled studies.
Preliminary results from a study in Scotland found that the Pfizer vaccine reduced hospital admissions by up to 85% four weeks after the first dose.
In comparison, the Oxford shot reduced admissions by up to 94%.
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In England, preliminary data from a study with healthcare professionals showed that the Pfizer vaccine reduced the risk of contracting COVID-19 by 70% after one dose, a number that increased to 85% after the second.
Health Secretary Matt Hancock said: “This new evidence shows that the jab protects you and those around you.
“It is important to see as much evidence as possible about the vaccine’s impact on protection and transmission and we will continue to publish the evidence as we gather it. ”
Although no figures have been reported on the effectiveness of the Pfizer vaccine in reducing transmission of the virus, the researchers behind the health study said it would cut transmission.
In December, experts advising the government, including the JCVI, said the second dose of vaccines should be delayed by up to 12 weeks, allowing more people to be vaccinated.
On Sunday, the government said all adults in the country should receive their first vaccine by July 31, at least a month before their previous target.
The new target also predicts that everyone aged 50 and over and those with an underlying health problem will have the first of the two vaccines by April 15, instead of the previous date of May 1.
Watch: What is COVID Long?