Mixing and matching coronavirus vaccines may help tackle variants, early data suggests
Mixing and matching coronavirus vaccines may be key to combat emerging variants, with early data suggesting a combination of AstraZeneca and Pfizer may trigger an immune response almost four times stronger than two doses of the same shot.
In a small trial involving 26 relatively young patients, German researchers found that the level of neutralising antibodies protecting against the variants first found in the UK and South Africa – now known as Alpha and Beta – was 3.9 times higher in those who had a mix of shots.
“Mixing vaccines is, I think, better for tackling everything,” he said. “You get less of a reduction in protective headroom [due to variants] by mixing and matching than by coming back with the same thing [vaccine] twice.”
Prof Altmann added that mixing shots may become more important if people do need a third dose, either to prolong immunity or protect against emerging variants.
“It’s nonsense to think that you’ll come back with the same [vaccine] over and over again forevermore,” he said. “In the end, you’d have so much pre-emptive immunity against the vaccine itself that it would never work.”
For instance, repeated doses of adenovirus based shots, such as Oxford-AstraZeneca, tend to become less effective over time as the immune system starts to respond to the virus rather than the Sars-Cov-2 spike protein. By contrast mRNA vaccines, like Pfizer-BioNtech and Moderna, are thought to trigger stronger side effects with added doses.
There are some limitations to the small German study, which was published as a preprint and has not yet been peer reviewed.
While there appears to be a strong correlation between the level of antibodies and the level of real world protection, the researchers involved warned more data is needed to ascertain the impact on transmission and disease.
“The four-fold difference we see is based on what we measured in the lab in our study, this doesn’t necessarily translate to four-fold higher protection in the real world, and the exact numbers will likely vary between studies,” said Rüdiger Groß, a virologist at the Ulm University Medical Center in southern Germany.
“But it is great to see that it works at least as well, possibly even a little better, than two BioNTech [vaccines], where protection is already very high.”
He added that more research in older people is also needed to confirm whether the mix and match approach – known as a heterologous, rather than homologous, regimen – also triggers a high level of neutralising antibodies to fight variants in this cohort. The average age in the study was just 30.
But the paper comes amid growing signs that mixing vaccines is safe and effective.
Separate trials of over 600 people in Spain and 300 in Germany found that using a combination of the AstraZeneca and Pfizer vaccines produces a potent immune response against the coronavirus, while early data from the UK’s Com-Cov trial – which is set to publish efficacy results in September – concluded that mixing the two vaccines is safe.
Experts say the results will provide much needed flexibility for UK and global vaccine rollouts.
“It means that lack of supply shouldn’t prevent us from giving people their second vaccine,” said Eleanor Riley, a professor of immunology and infectious Disease at the University of Edinburgh.
“The mixing and matching data is really positive, it suggests that at least mixing and matching is no worse than having the same vaccine twice – at best it gives you a much better immune response. And all the evidence we have is the better your immune response, the longer you’re going to be protected for the less likely you are to transmit.”
Prof Riley added that the data “suggests that we can move ahead with mixing and matching vaccines”, which has already happened in Canada.
The country’s National Advisory Committee on Immunisation said this week that Canadians can combine either the AstraZeneca, Pfizer or Moderna vaccines if the same first dose is unavailable or unknown.
Mixing vaccines could also help ease chronic supply challenges for the Covax vaccine distribution scheme. A Unicef official told the Telegraphlast week that this option is being explored after India banned vaccine exports, cutting off the supply of millions of AstraZeneca shots for countries across the globe.