With No Data, Mixing Vaccines a 'Dangerous Trend': WHO Head Scientist

"We are in a data-free, evidence-free zone as far as mix and match (is concerned)," the WHO scientist said.

The World Health Organization's head scientist Soumya Swaminathan addressed an online press briefing on Monday, 12 July, and referred to the fast-emerging trend of mixing and matching of different COVID-19 vaccines as "dangerous", advising beneficiaries against it.

Swaminathan stated:

"It's a little bit of a dangerous trend here. We are in a data-free, evidence-free zone as far as mix and match (is concerned)."

Soumya Swaminathan, as per Reuters

She added, "It will be a chaotic situation in countries if citizens start deciding when and who will be taking a second, a third and a fourth dose," Reuters reported.

Countries Allowing Mixing of Doses

Amid ongoing trials and based on preliminary data, several countries including Canada, Spain, Bahrain, and Germany among others have already started administering mixed shots.

Spain is presently allowing those who have received one dose of the AstraZeneca vaccine to receive a second dose of the Pfizer vaccine, while Bahrain is administering Pfizer-BioNTech booster shots to vulnerable residents who were previously vaccinated with the Chinese Sinopharm vaccines.

Meanwhile, on 1 June, the US announced the beginning of clinical trials to test the use of a different COVID vaccines in fully vaccinated adults as a booster shot.

Canada's National Advisory Committee on Immunization (NACI) also announced last month that people who received a first dose of the AstraZeneca vaccine may receive Pfizer-BioNTech or Moderna for their next shot.

The British government, too, had updated their vaccine guidelines allowing people to mix shots in case they were unaware of which dose was administered to them first.

However, the UK's deputy chief medical officer Prof Jonathan Van-Tam, said as long as the rollout was stable, there is no reason to change the same dose vaccine plan in the UK.

Other countries facing extreme vaccine paucity such as Bahrain have had to allow mixing of shots, while Germany, France, Norway, Thailand, and Sweden are also undertaking similar protocols.

Where India Stands

Following an incident in which at least 20 people were accidentally injected two different vaccines, the Indian government plans to launch a study on mixing of vaccines, which is reportedly to be completed in the next two months.

However, there has been no official change in the country's vaccination policy owing to the lack of clinical data.

However, according to a report by NDTV, the government is running a test to check the effectiveness of a single dose of Covishield.

The study will reportedly be completed in the next month.

Is Mixing Vaccines Safe? What Research Says

In India, VK Paul, NITI Aayog member and the head of India's COVID task force, has said that "in-depth research will be required to check whether mixing vaccines is effective".

A study led by researchers at the University of Oxford provided preliminary data on the subject and found that "mixing” the Oxford-AstraZeneca and Pfizer-BioNTech vaccines is safe, although it could cause more severe, albeit temporary, side effects.

However, it is important to note that all trials are in their early stages.

They also found that a mix-and-match of AstraZeneca and Pfizer vaccines gives a strong immune response.