Combining different coronavirus shots could speed immunization campaigns — and even boost immune response.
Researchers in the United Kingdom have launched a study that will mix and match two COVID-19 vaccines in a bid to ease the daunting logistics of immunizing millions of people — and potentially boost immune responses in the process.
Most coronavirus vaccines are given as two injections: an initial ‘prime’ dose followed by a ‘boost’ to stimulate the immune system’s memory cells and amplify the immune response. The clinical trial will test participants’ immune responses to receiving one shot of a coronavirus vaccine produced by Oxford and drug firm AstraZeneca — which uses a harmless virus to carry a key coronavirus gene into cells — and one shot of the vaccine produced by drug company Pfizer, which uses RNA instructions to trigger an immune response. The trial, which is run by investigators at the University of Oxford, aims to begin enrolment on 4 February.How COVID unlocked the power of RNA vaccines.
Vaccine developers often combine two vaccines to combat the same pathogen, and researchers are keen to deploy the strategy — known as a heterologous prime-boost — against the coronavirus. A heterologous prime-boost combination was approved last year by European regulators to protect against Ebola, and experimental HIV vaccines often rely on the strategy, says Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston, Massachusetts. But it has yet to be tested for vaccines against COVID-19, which are typically given as a repeat injection of the same vaccine.
The ability to mix and match vaccines could make vaccination programmes more flexible: it would speed up the process and reduce the impact of any supply-chain disruptions. “It really makes the implementation much more simple,” said Mary Ramsay, head of immunization at Public Health England, at a press briefing on 3 February.
Oxford has said that it will also trial combinations of its COVID-19 vaccine with the Russian coronavirus vaccine, Sputnik V, which uses harmless viruses to shuttle components of the coronavirus into cells. Sputnik V, which this week was shown1 to have greater than 90% efficacy against COVID-19, is itself a heterologous prime-boost vaccine, consisting of different viral components in the first and second doses.
Some researchers also think that combining two vaccines could strengthen immune responses by harnessing the best features of each. That would be particularly desirable now that vaccine developers are combating coronavirus variants that seem to be partially resistant to certain immune responses, says Barouch. “It’s possible that responses might be better than what either vaccine can achieve on its own,” Barouch says. “But that remains to be proven experimentally for COVID-19.”
The Oxford trial aims to enrol 820 people, and it will test two dosing schedules: one with 4 weeks between the two injections, and another with a 12-week interval. The trial will not look directly at how well the combination protects against COVID-19 — such a study would need to be much larger and would take a long time to complete. Instead, the team will take regular blood samples to measure levels of antibodies and immune cells called T cells that participants produce against the coronavirus. It will also monitor for safety concerns.Original Source