As the highly contagious Delta variant of the coronavirus spreads in dozens of countries around the world, some governments are mixing vaccines in an attempt to increase their vaccination motivation.
A mixed vaccine is to give a patient a first injection of a brand of vaccine, and then a second dose of a vaccine produced by a different manufacturer. Supporters of the policy believe that it can increase the speed and effectiveness of the vaccination campaign.
Several ongoing studies are investigating the impact of mixed coronavirus injections. Data from mixed trials in Spain and the United Kingdom show that mixed vaccines produce a strong immune response, sometimes even better than two doses of the same vaccine.
In Germany, the third study also showed that the immune response of the mixed coronavirus dose was better than that of two AstraZeneca vaccines and was as good or better than the immune response of receiving two doses of Pfizer vaccine.
Which countries are mixing vaccines?
Many countries including Bahrain, Bhutan, Canada, Italy, South Korea, Thailand and the United Arab Emirates it has started Mixed vaccines as a policy.
This practice was quietly approved by Public Health England in January, when the vaccine supply restricted.
In the same month, US media reported that the US Centers for Disease Control and Prevention relaxed its recommendations for authorization. mixing “under special condition”.
In March, some countries suspended vaccine promotion activities due to fears of extremely rare situations. Blood clot Related to the Oxford-AstraZeneca vaccine.
In response, in some countries, medical staff is authorized For some patients who received AstraZeneca for the first time, they were given a different vaccine for the second time.
Dr. Gloria Taliani, professor of infectious diseases at the University of Sapienza in Rome, told Al Jazeera that in the past, mixed use was commonplace in the treatment of other diseases.
“We used different vaccines [when we treated] For other diseases, we don’t care whether the second dose is different from the first dose, or whether the booster dose is different. “
Dr. Tagliani pointed out that since this is the first time, there may be some problems mRNA vaccine It has been used to prevent infectious diseases, but said that there is no biological reason to indicate that mixing may be dangerous.
“There is no biological reason that the use of differently stimulating vaccines on the immune system may be harmful to anyone,” she explained.
In recent months, several world leaders have mixed vaccines. German Chancellor Angela Merkel, 66 years old, received Receive the second dose of Moderna vaccine after receiving the first dose of AstraZeneca.
In Italy, 73-year-old Prime Minister Mario Draghi switched to Pfizer for a second injection after receiving an AstraZeneca injection.Canadian Prime Minister Justin Trudeau Switch vaccine, Received Moderna injection after AstraZeneca injection.
Is the mixed COVID vaccine effective?
Oxford University Com-COV test, Involving more than 800 volunteers, investigated the efficacy of two doses of AstraZeneca, Pfizer or one of them.
According to the results, the mixed plan of Pfizer vaccine and AstraZeneca vaccine produced a strong immune response against the virus.
Research result Suggest The order of the vaccines is different. AstraZeneca and Pfizer “induce higher antibody and T cell responses than Pfizer and AstraZeneca.”
T cells stimulate the production of antibodies and help fight virus-infected cells. The study also showed that the two doses of Pfizer produced the highest levels of antibodies.
Compared with the two doses of AstraZeneca vaccine, which are still very effective, these two mixtures produced better results.
In addition, in May, a Spanish study involving more than 600 volunteers Established One dose of AstraZeneca, then Pfizer, is more effective than two doses of AstraZeneca.
However, experts say that there is insufficient clinical data to fully determine whether the blending is effective.
Dr. Anna Blakney, an assistant professor in the Michael Smith Laboratory and School of Biomedical Engineering at the University of British Columbia, was a member of a team that conducted a trial that looked at a hybrid mRNA vaccine and AstraZeneca virus vector vaccine.
“What we saw in mice is that combining the two is more effective than using one of them alone,” she said.
“So I think it can work, but we don’t have data yet to show whether this is a truly effective system.”
Is the mixed COVID vaccine safe?
There are no research results that show that mixing can cause serious side effects, but the results of a British study show that mixed vaccines can cause an increase in mild or moderate side effects.
Com-COV research data shows that 30% to 40% of people received Fever after the second vaccination was reported for mixed doses, compared with 10% to 20% of people who did not mix the vaccine.
“The results of this study indicate that the mixed-dose schedule may lead to increased absences from work on the second day after immunization, which is important when planning immunizations for medical staff,” said Dr. Matthew Snape, associate professor of pediatrics and vaccinology at the hospital. Oxford University and the lead investigator of the trial said at the time.
The ongoing Com-COV trial was expanded in April to include Moderna and Novavax vaccines.
The results of the Spanish study found that minor side effects were common and similar to those reported for the same vaccine in two doses.
At the same time, Soumya Swaminathan, the chief scientist of the World Health Organization, warned individuals not to choose a mixed vaccine and said that the health agency should make the decision.
“Individuals should not decide for themselves, public health agencies can use existing data,” Swaminathan said in a tweet. “Awaiting data from a mix and match study of different vaccines-both immunogenicity and safety need to be evaluated.”