A mixed COVID-19 vaccination schedule, administering the AstraZeneca (AZ) vaccine as the first dose and the Pfizer/BioNTech jab as the second dose, boosts neutralising antibody levels six-fold compared to two AZ doses, according to researchers.
The South Korean study enrolled a total of 499 medical workers, with 100 of those receiving the mixed vaccination schedule, 200 receiving two doses of the Pfizer/BioNTech jab and the remaining receiving two doses of the AZ vaccine.
While all participants developed neutralising antibodies against the SARS-CoV-2 virus, participants who received the mixed AZ/Pfizer vaccine regimen had similar antibody levels to participants who had two doses of the Pfizer/BioNTech vaccine – both of these induced higher antibodies than two doses of the AZ vaccine.
In June, a UK study also suggested that mixing COVID-19 vaccines as part of a two-dose schedule generates a strong immune response against the SARS-CoV-2 virus.
The first results from the Oxford University-led 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.
Notably, administering a first dose of the AZ vaccine followed by the Pfizer/BioNTech vaccine induced both higher antibody levels and T-cell responses compared to Pfizer/BioNTech followed by AZ.
Both of these mixed regimens induced higher antibodies than the standard two-dose AZ 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.
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.