The Washington PostDemocracy Dies in Darkness

Covid-19 global updates Some countries defend mixing vaccines after WHO suggests booster strategy is ‘chaotic’

A health worker prepares a dose of the Oxford-AstraZeneca coronavirus vaccine at an immunization center in Bangkok on July 13. (Sirachai Arunrugstichai/Getty Images)
Placeholder while article actions load
Please Note

The Washington Post is providing this important information about the coronavirus for free. For more free coverage of the coronavirus pandemic, sign up for our Coronavirus Updates newsletter where all stories are free to read.

Canadian and Thai health officials are defending the decision to mix different coronavirus vaccines after the World Health Organization’s chief scientist suggested this week that combining doses was potentially unsafe.

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 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 dose of the adenovirus-based Oxford-AstraZeneca vaccine. “We have taken some strong decisions that quite frankly, are bearing out,” Canadian Prime Minister Justin Trudeau told reporters Tuesday.

Here are some significant developments:

  • Parts of South Africa’s vaccination program were temporarily halted following the country’s most violent protests in years. Only about 2.5 percent of the covid-ravaged nation’s population has been fully inoculated.
  • The city of Tokyo on Wednesday reported its highest number of coronavirus cases in nearly six months, just days ahead of the Olympic Games and about a week after authorities declared a state of emergency to stem the rising tide of infections.
  • The global number of new coronavirus cases rose by 10 percent over the past week, after more than two months of steady decline, the WHO said in an epidemiological update. While the number of deaths linked to covid-19 increased by 3 percent worldwide, the agency said, the Africa region recorded a 50 percent jump in new fatalities from the virus.
  • London’s transport authority will reportedly continue mandating face coverings aboard services such as the city’s subway system. England will lift virtually all remaining virus curbs on Monday.
  • Sydney extended its limited lockdown by at least another 14 days, after New South Wales state logged 97 new cases on Wednesday. Australia’s largest city has been under enhanced restrictions for about three weeks.

A statement issued by Ontario’s health minister noted 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 Oxford-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 people who received a first Oxford-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 it would allow those who were administered a first Oxford-AstraZeneca shot to get Pfizer-BioNTech mRNA coronavirus 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. (More than 600 Thai health workers who were fully inoculated with the Sinovac shot later caught the virus.)

The goal of mixing the British-Swedish Oxford-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 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 serves as the director of NIH’s National Institute of Allergy and Infectious Diseases.

Katerina Ang in Seoul contributed to this report.

Sign up for our coronavirus newsletter | Mapping the spread of the coronavirus: Across the U.S. | Worldwide | Vaccine tracker