UK Tests Pfizer/AstraZeneca Vaccine Combination Regimen in Older Patients

UK researchers launched a new study yesterday to assess a combined COVID-19 vaccination regimen in older adults that includes the Pfizer/BioNTech and the AstraZeneca (AZ)/Oxford University vaccines.

The use of different vaccines in sequence to boost immune responses — known as “heterologous boosting” — is not a new idea, but it’s gaining renewed interest as the world faces supply shortages that may call for flexibility between different vaccine doses.

By mixing the vaccines, the researchers at the National Institute for Health Research hope to determine whether shots can be used interchangeably as part of the dosing schedule. If the interim findings, slated to be released in June, are positive, nations could ease supply shortages by administering whatever doses are available for the second shot.

Participants in the multi-arm trial will receive either two shots of the AZ/Oxford vaccine, an initial dose of the AZ/Oxford vaccine followed by the Pfizer/BioNTech vaccine, or two shots of the Pfizer/BioNTech vaccine – with each second dose to be given within four to 12 weeks. The trial aims to enroll more than 800 participants aged 50 years and older across eight clinics in England for a period of 13 months.

The UK team will then collect blood samples to assess the level of antibodies induced and the efficacy of different dosing intervals and will also monitor for any adverse events.

The data gathered on the AZ vaccine for older adults will have particular importance because of the scarcity of data in this population for the vaccine. When the European Commission granted the AZ vaccine a conditional marketing authorization last week, EU member states, including Germany and France, expressed concern about the lack of supporting data for older patients (DID, Feb. 1).

The study is being widely welcomed by the medical community. Ali Mirazimi, a vaccine specialist at Sweden’s Karolinska Institute, saidhe sees no safety issue in combining the vaccines based on available data, especially since the trial will follow established dosing intervals. And Brian Wispelwey, an infectious diseases specialist at the University of Virginia, concurred, stating that “safety is less a concern than efficacy,” given that it would be hard for the combined regimen to surpass Pfizer’s two-dose 95 percent efficacy.

Since the Pfizer/BioNTech vaccine is “the most difficult to deal with” because of its ultra-cold storage requirements, “one has to believe this is a way to get more vaccine out there,” Wispelwey said. Matti Sallberg, vaccinologist and department head from the Karolinska Institute, agreed, predicting countries will have to eventually use the heterologous boosting strategy, which has been employed for other viruses, including Ebola, malaria and tuberculosis. — Jason Scott