We need to have the best idea. A small number of trials are now underway to test the power of the vaccine combinations, with initial results to be completed by the end of this month. If these blending regimens prove safe and effective, countries will be able to continue to operate the vaccine even if supplies of a vaccine are reduced due to production delays, unexpected shortages, or concerns. of safety.
But there is another, more interesting prospect that will be an important part of our strategy in the future: mixing vaccines could lead to greater resistance and hinder virus tests that evade our immune systems. Later, a method of mixing and matches would be the best way to protect ourselves.
Covid-19 vaccines are currently used to protect against the virus in slightly different ways. Most target the coronavirus spike protein, which it uses to gain penetration into our cells. Yet some deliver instructions for making the protein in the form of messenger RNA (Pfizer, Moderna). Some deliver spike protein itself (Novavax). Some use another harmless virus to ferry instructions for doing so, such as a Trojan horse (Johnson & Johnson, Oxford-AstraZeneca, Sputnik V). Some offer entirely inactive virus (Sinopharm, Sinovac).
In a study published in March, researchers from China’s National Institutes for Food and Drug Control examined combinations of four different covid-19 vaccines in mice, and found that some improved the resistance response. When they first gave the mice a vaccine that relied on the harmless cold virus to pass the instructions and after a second dose of a different vaccine, they saw significantly higher antibody levels and a better T-cell response. But when they changed the order, given the viral vaccine second, they didn’t see a single improvement.
Why combining shots can improve effectiveness is a mystery, according to Shan Lu, a physician and vaccine researcher at the University of Massachusetts Medical School who promotes this method of mixing. “The mechanism we can explain in part, but we don’t fully understand.” Different vaccines present the same information in slightly different ways. Those variations can awaken different parts of the immune system or sharpen the immune response. This method can also prolong resistance.
Even if the consequences people interpret it continue to be seen. Researchers at Oxford University have launched a human test to test how to mix. The study, called Com-CoV, offered participants a first shot of Pfizer or Oxford-AstraZeneca. For their second dose, they get the same vaccine or a shot of Moderna or Novavax. The first results should be available in the coming weeks.
Other studies are also ongoing. In Spain, where Oxford-AstraZeneca is now given to people over 60, researchers plan to recruit 600 people to test whether the first dose of the shot can be paired with a second dose from Pfizer. According to a report in El País, about one million people received the first dose of the vaccine but were not old enough to receive the second dose. Health officials are waiting for the results of this study before issuing recommendations for this group, but it is unclear if any participants have been recruited.
Late last year Oxford-AstraZeneca announced it would partner with Russia’s Gamaleya Institute, which produces the Sputnik V vaccine, to test how the two shots combine. The trial was supposed to launch in March and give unmixed results in May, but it’s unclear when it will start. And Chinese officials have indicated they will examine the mix of vaccines to improve the effectiveness of their shots.
The most gain can be obtained from a mixture of vaccines that have less effectiveness. The mRNA vaccines from Pfizer and Moderna provide excellent protection. “I don’t think there’s any reason to mess with that,” said Donna Farber, an immunologist at Columbia University. But the mix could improve protection for some vaccines that report higher levels of protection, such as Oxford-AstraZeneca and Johnson & Johnson, as well as some vaccines in China. Many of these vaccines work well, but mixing can help them work even better.