The WHO's Soumya Swaminathan said in a briefing Monday that plans by some countries to administer booster shots signaled a "dangerous trend" that could lead to "a chaotic situation . . . if citizens start deciding when and who will be taking a second, a third and a fourth dose."
"We are in a bit of a data-free, evidence-free zone as far as 'mix-and-match,'" she said. She later clarified on Twitter that she was concerned about individuals, rather than public health agencies that she said would have better data, deciding to get a mixed cocktail of shots.
A top Thai virologist fired back Tuesday, however, saying that authorities would forge ahead with plans to mix a first dose of the Sinovac vaccine with a second dose of the Oxford-AstraZeneca shot.
Canadian public health officials also defended their plan to offer messenger RNA vaccines as a second shot to people who received a first AstraZeneca dose. "We have taken some strong decisions that quite frankly, are bearing out," Canadian Prime Minister Justin Trudeau told reporters Tuesday.
A statement issued by Ontario's health minister noted that the province's booster-shot program was "based on studies from the [United Kingdom], Spain and Germany that have found mixing vaccines is safe and produces a strong immune response."
Canada's mixed inoculation program came after the AstraZeneca shot was found to cause potentially fatal blood clots in a very small number of recipients, most of them young people.
A number of countries, including in Europe, have followed similar tracks, recommending that people who received a first AstraZeneca dose then follow up with an mRNA vaccine.
Vietnam, which is battling a wave of infections caused by the more contagious delta variant, said Tuesday that it would allow those who were administered a first AstraZeneca shot to get the Pfizer-BioNTech vaccine as a second dose.
Thailand, however, is seeking to bolster immune response amid questions over the Sinovac vaccine's effectiveness against the delta variant and as it attempts to quash its worst outbreak of the pandemic. (Over 600 Thai health workers who were fully inoculated with the Sinovac shot later caught the virus.)
The goal of mixing the AstraZeneca and Chinese-made shots, chief virologist Yong Poovorawan said, is to reach a "booster" effect in a shorter period of time.
"We can't wait 12 weeks [for a booster effect] in this outbreak where the disease is spreading fast," he said, according to Agence France-Presse.
Researchers in Britain, Russia and the United States are all currently conducting clinical trials testing mixed-shot vaccine regimens.
In June, the U.S. National Institutes of Health said it was starting a trial in which fully vaccinated adults would be given a booster dose of different coronavirus vaccines.
"We need to prepare for the possibility of needing booster shots to counter waning immunity and to keep pace with an evolving virus," the country's top infectious-disease expert, Anthony S. Fauci, said in a statement announcing the study.
"The results of this trial are intended to inform public health policy decisions on the potential use of mixed vaccine schedules should booster doses be indicated," said Fauci, who also serves as the director of NIH's National Institute of Allergy and Infectious Diseases.
Published : July 14, 2021
By : The Washington Post · Erin Cunningham