Mixing and matching the dosing regimens for the coronavirus vaccines developed by Pfizer
Researchers behind the Com-COV study, which is looking into how effective using one vaccine for the initial "prime" vaccination followed by a different "booster" shot, found that alternating doses of the mRNA- and vector-based vaccines produced strong immune responses.
However, the order of the vaccines matters for the greatest protection, with the AstraZeneca vaccine followed by the booster shot of Pfizer generating the strongest immune response out of the two dosing schedules.
Under the trial, doses of either vaccine regimen were given four weeks apart. Researchers expect to present data for the 12-week dose interval, which is the maximum recommended for AstraZeneca's vaccine in the United Kingdom, in the coming weeks.
The study was published in pre-print for The Lancet to peer-review.
The positive results of this mix and match study come as nations are looking to vaccinate as many people as possible as the highly contagious, and possibly more deadly, Delta variant becomes the most dominate COVID strain worldwide.
The Delta variant, which first emerged in India, is classified as a Variant of Concern by both the World Health Organization and U.S. Centers for Disease Control and Prevention due to the mutant strain's high transmission rate and concern that it may derail progress towards containing the global disease outbreak.
"It is the most hypertransmissible, contagious version of the virus we've seen to data, for sure--it's a superspreader strain if there ever was one," said Eric Topol, a professor of molecular medicine and an executive vice president at Scripps Research Institution, quoted by Scientific American.
The Delta variant is also more elusive to the antibodies generated by the current generation of COVID vaccines, making fully vaccinated individuals at risk of infection. Some health experts have grown concerned about the level of protection produced by the Johnson & Johnson
Although data is sprace, Moderna's vaccine showed promise against the Delta variant in a lab setting. The company said the two-dose mRNA vaccine produced neutralizing antibodies against Delta, with the results based on the blood serum of eight participants taken one week after their receive the second dose of the vaccine; the data may not reflect how the vaccine will perform in real-world scenarios.