WHO warns against mixing and matching COVID-19 vaccines

WHO warns against mixing and matching COVID-19 vaccines after Canada and Thailand give patients several injections

  • WHO warned against mixing and matching COVID-19 vaccines, saying long-term effects are unknown
  • In Thailand, officials plan to mix the Sinovac and AstraZeneca vaccines to counter the recent surge in cases
  • In Canada, health officials are recommending people who have received one injection of the AstraZeneca vaccine the Pfizer or Moderna vaccine for their second dose
  • The NIH has launched trials in the US to find results of mixing vaccine types for a third booster injection

The World Health Organization (WHO) warned on Monday against mixing different types of two-shot COVID-19 vaccines.

WHO experts say little data is available on the health effects of mixing different shots.

The warning comes after Thailand announced it would allow patients to receive one injection each of its AstraZeneca and Sinovac vaccines to combat a current wave of COVID-19 cases.

Canada also announced last month that residents who receive the AstraZeneca vaccine for their first shot must receive the Pfizer-BioNTech or Moderna vaccine for their second illness.

“It’s a bit of a dangerous trend here. We are in a data-free, evidence-free zone in terms of mix and match,” said WHO chief scientist Dr Soumya Swaminathan at a briefing on Monday.

‘It will be a chaotic situation in countries when citizens decide when and who takes a second, third and fourth dose.’

Thailand will mix the Sinovac and AstraZeneca vaccines for health workers, a move the WHO advises against. Pictured: A Thai citizen gets a vaccine in Bangkok

Thailand is currently suffering the largest increase in cases since the start of the pandemic.

The Southeast Asian nation records an average of 6,695 new cases per day, and the total is likely to grow even more in the coming days.

The number of cases is 162 percent higher than a month ago on June 11 and 1,239 percent higher than three months ago on April 11.

The infections included 618 breakthrough cases among 677,000 medical personnel who were fully vaccinated with the Sinovac vaccine — or 0.1 percent of people.

The Sinovac vaccine was developed in China and distributed to neighboring Asian countries.

Thailand now plans to give medical staff the AstraZeneca vaccine for their second injection with just one injection of the Sinovac vaccine.

In Canada, people who have received the AstraZeneca vaccine for their first injection are advised to get the Pfizer vaccine for their second injection.  Pictured: Canadian Prime Minister Justin Trudeau gets his second shot of the vaccine

In Canada, people who have received the AstraZeneca vaccine for their first injection are advised to get the Pfizer vaccine for their second injection. Pictured: Canadian Prime Minister Justin Trudeau gets his second shot of the vaccine

Canadian health officials made a similar decision last month.

On June 18, Canada’s National Advisory Committee on Immunization said people who received the AstraZeneca COVID-19 vaccine as their first dose should receive the Pfizer-BioNTech or Moderna for their second dose.

“New evidence is beginning to emerge suggesting that immune responses are better when a first dose of the AstraZeneca vaccine is followed by an mRNA vaccine as the second dose,” said Dr Shelley Deeks, vice-chair of the committee, in the new guidelines.

The Pfizer and Moderna vaccines are the two available vaccines that use mRNA technology.

The committee also updated its previous recommendation that people at high risk of exposure to or severe illness from COVID-19 may choose to receive AstraZeneca rather than wait for Pfizer or Moderna.

Now it says everyone should always get the mRNA vaccines first unless they are allergic to them.

Deeks said the advice is based on the growing offerings from Pfizer and Moderna, and the risk of vaccine-induced blood clots associated with AstraZeneca.

But she still tries to reassure people who have received one or two doses of AstraZeneca’s vaccine that they are well protected after all.

“Anyone who has already received two doses of AstraZeneca/Covishield can rest assured that they are protected, especially against serious illnesses,” she said.

“A third dose is not necessary at this time.”

However, some Americans may soon require a third dose, and it is currently being investigated whether mixing vaccine brands for the third injection is safe.

Last month, the National Institute of Health launched a trial where they gave Americans who had received two injections of Pfizer or Moderna and then received Moderna for their third dose.

The aim is to discover whether there are potential benefits to mixing and matching different vaccines.

The first results of the study are expected by the end of the summer and data from the study will be collected throughout the year.

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