Can ‘mixing and matching’ Covid vaccines boost protection?

A trial examining whether a combination of two different Covid vaccines could provide more effective protection against the virus is calling for volunteers.

The researchers behind the project - dubbed Com-Cov - are looking for people aged 50 and over to take part in the government-backed study.

The trial will compare the impact of giving a dose of the AstraZeneca-Oxford jab followed later by the Pfizer-BioNTech version - and vice versa. Run by the National Immunisation Schedule Evaluation Consortium, it will be based in eight hospitals in England.

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Professor Matthew Snape, an Oxford University vaccine expert who is leading the trial, told Sky News: “We are looking to unroll the trial this month and then would start to get results through, probably in June or July, looking at the antibody levels at least.”

“Viral-based vaccines such as the Oxford jab, which is based on a chimp common cold virus, give a much greater cellular response - prompting the T-cells to kill cells infected with the coronavirus,” The Guardian says.

“The mRNA vaccines, like Pfizer’s, tend to generate a bigger antibody response”, the paper adds, leading to the hypothesis that giving patients one shot of each will generate a more powerful and long-lasting immune response to Covid-19.

Kate Bingham, chair of the government’s vaccine task force, has given her backing to the study, explaining that “antibodies block the uptake of viruses into cells and the cellular T-cells identify those cells that have been infected and take them out. You ideally want to have both”.

The process of mixing vaccines is known as heterologous boosting and has previously been used in “some Ebola immunisation programmes... to improve protection”, the BBC reports.

Vaccines minister Nadhim Zahawi said the government’s taskforce had given about £7m to fund the study, adding that similar studies have been done with other vaccines such as jabs for hepatitis, polio and measles, mumps and rubella.

The results of the study are expected to become available in the summer.