The UK has drawn up plans that would allow patients to be given different coronavirus vaccines for the first and second doses under certain circumstances, a move that highlights a widening rift in public health policy between the UK and rest of the West.
The government’s Green Book for vaccinations says “every effort” should be made to complete the immunisation course with the same vaccine. But it also says: “For individuals who started the schedule and who attend for vaccination at a site where the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product to complete the schedule.”
Health officials said this would only happen under very limited circumstances.
Mary Ramsay, Head of Immunisations at PHE, said mixing Covid-19 vaccines was not recommended. “If your first dose is the Pfizer vaccine you should not be given the AstraZeneca vaccine for your second dose and vice versa.
“There may be extremely rare occasions where the same vaccine is not available, or where it is not known what vaccine the patient received,” Dr Ramsay said. “Every effort should be made to give them the same vaccine, but where this is not possible it is better to give a second dose of another vaccine than not at all.”
The guidelines say this would involve individuals who are likely to be at high risk or unlikely to attend the appointment again.
The two UK-approved vaccines share the same mode of action, targeting the spike protein of the virus, which makes it “likely the second dose will help to boost the response to the first dose”, the rubric says.
The Oxford vaccine was approved at the end of December, when the Green Book chapter in question, number 14, was updated, according to the government website hosting it.
Stephen Evans, a professor in pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, told the Financial Times the approach was “not supported by randomised trial evidence”.
He noted, however, that a randomised trial on vaccine mixing had been announced in the UK. The reason such a trial had been suggested, even before any vaccine was authorised, was that there were “theoretical reasons” for believing that mixing and matching vaccines could yield greater efficacy than using two doses of the same vaccine, he added.
Jonathan Stoye, a virologist at The Francis Crick Institute, said mixing different vaccines on an emergency basis “does not seem unreasonable and is akin to wartime medicine”. But he added: “It should not become routine practice without stringent investigation.”
UK health officials rejected suggestions that the guidance implied a change of tactics. One said: “The UK has not moved to a mix-and-match regimen.” The approach would be used in exceptional circumstances where the only alternative was not to complete a vaccination course, they said. In practice it would be used rarely if at all, the official added.
Crucially, combination trials, including one studying the AstraZeneca and Sputnik V jabs, have not yet completed, and the UK’s move apparently reflects what experts have described as a pragmatic, if “go-it-alone”, approach amid rapidly rising case numbers.
The US Centers for Disease Control, one of the most prominent public health authorities globally, says coronavirus vaccines are not interchangeable. The BioNTech and Oxford vaccines use different technologies. The approach also appears to be discouraged in Europe.
UK health authorities have said vaccine shortages are a reality that “cannot be wished away”, and appear to be pursuing a strategy designed to balance risk and benefit amid challenging circumstances.
European authorities do not expect to approve the AstraZeneca vaccine before February, because they do not have enough data. US regulators have said the same. Moncef Slaoui, the head of US Operation Warp Speed, the US government’s effort to manufacture and procure vaccines for the country, said approval was not expected until April.
Disquiet is growing over the UK’s decision to change the dosing regimens for the two coronavirus vaccines it has approved, as experts question the justification for the long period between the first and second jabs. US experts have said they would not recommend diverging from what has been tested and tried in trials.