Britain explores value of mixed jabs

The United Kingdom has launched a clinical trial to determine whether alternating doses of the Oxford and Pfizer vaccines can provide effective protection against the coronavirus. If so, the mixed treatments could offer greater flexibility for vaccine rollouts.

In the government-funded study, some volunteers will receive a first dose of the vaccine from the University of Oxford and AstraZeneca, followed by a second dose of the shot from Pfizer and BioNTech. Other participants will receive the jabs in reverse order.

Researchers will then test antibody levels to ascertain whether the mixed treatments provoke an immune response that is weaker, stronger, or on par with conventional dosing.

Having the option to mix treatments would be beneficial during times when certain vaccines are in short supply.

"Given the inevitable challenges of immunizing large numbers of the population against COVID-19 and potential global supply constraints, there are definite advantages to having data that could support a more flexible immunization program, if needed," said Jonathan Van-Tam, deputy chief medical officer for England.

Several studies into inoculations aimed at combating HIV, malaria, and tuberculosis have provided evidence that alternating candidate vaccines can provoke an immune response that is as good if not greater than relying on a sole treatment.

Similar goal

The method is known as heterologous prime-boosting, and there is reason to believe it may work in the case of the Pfizer and Oxford treatments because, while they use very different means, both inoculations have a similar goal.

The two vaccines help the immune system recognize and disrupt the same protein that the novel coronavirus relies upon to gain entry into cells.

The government said it will not implement such a dosing policy if the results suggest it would result in lower levels of protection. But there is a chance that the approach could provoke a stronger immune response.

"It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer," said Van-Tam. "Unless this is evaluated in a clinical trial, we just won't know."

The 7-million-pound ($9.6 million) study will be run by the UK National Immunization Schedule Evaluation Consortium and involve 800 volunteers.