Mixing COVID-19 vaccines as part of a two-dose schedule generates a strong immune response against the SARS-CoV-2 virus, a study led by Oxford University suggests.
The Com-Cov study was initially launched in February, becoming the first trial in the world to evaluate whether different vaccines can be used safely and effectively as part of two-dose regimens.
The first results from the study suggest that two mixed schedules – a first dose of the Pfizer/BioNTech vaccine followed by the AstraZeneca/Oxford University vaccine or a first dose of the AstraZeneca/Oxford University vaccine followed by the Pfizer/BioNTech vaccine – provide good protection against COVID-19.
Specifically, these mixed vaccine schedules induced high concentrations of antibodies against the SARS-CoV-2 spike IgG protein when the doses were given four weeks apart.
However, the researchers did note some differences between the vaccine regimens, with certain schedules inducing higher antibodies and T-cell responses compared to others.
Notably, administering a first dose of the AZ/Oxford vaccine followed by the Pfizer/BioNTech vaccine induced both higher antibody levels and T-cell responses compared to Pfizer/BioNTech followed by AZ/Oxford.
Both of these mixed regimens induced higher antibodies than the standard two-dose AZ/Oxford vaccine schedule, while the highest antibody response was observed following the standard two-dose Pfizer/BioNTech schedule.
Researchers also discovered that the AZ/Oxford vaccine followed by the Pfizer/BioNTech vaccine induced the highest T-cell responses.
“Today’s data [is] a vital step forward, showing a mixed schedule gives people protective immunity against COVID-19 after four weeks. Equally, they offer supportive evidence that the standard (non-mixed) JCVI recommendations for COVID-19 vaccination all produce highly satisfactory immune responses, for both main vaccines in use,” said Jonathan Van-Tam, deputy chief medical officer.
“Given the UK’s stable supply position there is no reason to change vaccine schedules at this moment in time. The results for the 12-week interval, which are yet to come, will have an instrumental role to play in decisions on the future of the UK’s vaccination programme,” he added.
AZ reveals new data for its Vaxzevria COVID-19 vaccine
AZ has also revealed new data from a sub-analysis of two Oxford University-led trials, showing that its vaccine – marketed as Vaxzevria in the EU – induced strong immune responses following a delayed second dose interval of up to 45 weeks or after a third booster dose.
When the interval between the first and second dose of the vaccine was extended by up to 45 weeks, antibody responses increased 18-fold, as measured 28 days after the second dose.
In addition, with a 45-week dosing interval between the first and second doses of the vaccine, antibody titres were four times higher than with a 12-week interval.
The researchers also found that a third dose of Vaxzevria, administered at least six months after the second dose, increased antibody levels six-fold and also induced higher neutralising activity against the Alpha, Beta and Delta variants.