In January, Britain made a change to its vaccine guidelines that shocked many health experts: If the second dose of one vaccine wasn’t available, patients could be given a different one.
The new rule was based on sheer guesswork; there was no scientific data at the time demonstrating that mixing two coronavirus vaccines was safe and effective. But that may change soon.
In February, researchers at the University of Oxford began a trial in which volunteers received a dose of the Pfizer-BioNTech vaccine followed by a dose of AstraZeneca’s formulation, or vice versa. This month, the researchers will start analyzing the blood of the subjects to see how well the mix-and-match approach works.
As growing numbers of vaccines are being authorized, researchers are testing other combinations. A few are in clinical trials, while others are being tested in animals for now.
created an Ebola vaccine whose first dose contained a virus called an adenovirus. The second shot used another virus, called vesicular stomatitis virus.
When the Covid-19 pandemic began last year, the Gamaleya researchers used a similar strategy to create vaccines against the new coronavirus. The first dose used the same adenovirus as in their Ebola vaccine, called Ad5. The second dose contained a different human adenovirus, Ad26. The researches inserted a gene into both viruses for the protein on the surface of the coronavirus, called spike.
Studies revealed that the vaccine, now known as Sputnik V, provided a strong defense against Covid-19. In clinical trials, the researchers found that it had an efficacy of 91.6 percent. Sputnik V is now in use in Russia and 56 other countries.
Recently, the Gamaleya institute joined forces with AstraZeneca, which makes its own Covid-19 vaccine. AstraZeneca’s consists of two doses of a chimpanzee adenovirus called ChAdOx1. Last week, the company reported that its vaccine had an efficacy of 76 percent.
found that the mixture worked better than two doses of the spike or of the R.B.D.
The researchers suspect that the first dose produces a broad range of antibodies that can stick to spots along the length of the spike protein, and that the second dose delivers a big supply of particularly potent antibodies to the tip of the spike. Together, the assortment of antibodies does a better job of stopping the coronavirus.