In Southeast Asia, Thailand on July 12 began giving the second shot of AstraZeneca vaccine to people who had been injected with Chinese-made Sinovac vaccine. The Bangkok Post on July 13 called the Thai government's permission to combine the Sinovac and AstraZeneca vaccines ‘a shift of viewpoint’.

Photo: Some studies from the UK, Germany and Spain show that the combination of vaccines increases the amount of antibodies.

American television channel CNN asked whether the combination of vaccines protect people better and if it necessary. Many studies have been conducted and are being implemented to better understand the benefits and risks of this approach.

Actually, this is not a new idea. Researchers tested this method in the fight against other diseases like Ebola.

Scientists argue that giving two doses using different types of vaccines could induce a stronger immune response, either by stimulating different parts of the immune system or by teaching the immune system to recognize different components of an invading pathogen.




In addition to the potential immunological benefits, the combination of different vaccines also offers flexibility when vaccine supplies are uneven or limited, according to Zhou Xing, an immunologist from McMaster University in Canada.

Photo: Tests showed that the combination of vaccines makes the antibody to increase 10 times compared to the two injections using AstraZeneca vaccine only.

According to research in the UK, Germany, and Spain, combining a dose of AstraZeneca vaccine with a dose of Pfizer triggered a much stronger immune response than injecting two doses of AstraZeneca vaccine.

According to Reuters, in May, scientists from the University of Oxford (UK) said that patients who received a combination of AstraZeneca and Pfizer vaccines developed significantly higher amount of antibodies than those who got two shots of AstraZeneca vaccines.

As part of a trial called Com-COV, researchers gave vaccinations combining different types of vaccines to 830 volunteers who were over 50. Those who got two doses of BioNTech's Pfizer vaccine had the highest antibody amount, followed by those who received the first dose from AstraZeneca and the second dose from the Pfizer vaccine. Reversing the order of injections also gave higher antibody results than those who received two doses of AstraZeneca vaccine.



A study by German scientists at the University of Saarland and a test called CombivacS in Spain with 663 participants revealed similar results.

Preliminary data from Com-COV indicates that the combination of vaccines may increase side effects such as fever, headache, and fatigue. However, these side effects are short-term and most subside after 48 hours. In addition, side effects can also be signs of a strong immune response.

Recommendations for vaccine combination



Although the initial results are promising, most of the studies are in the early stages and have not been fully evaluated scientifically, according to scientists.

The World Health Organization (WHO) still recommends not combining vaccines. WHO spokeswoman Margaret Harris recently stated that there was not enough data to assess whether the combination of vaccines is safe.

The trend of mixing and matching Covid-19 vaccines is “dangerous”, given the limited availability of data on the safety of administering different types of vaccines, WHO chief scientist Soumya Swaminathan warned on July 12.

“So it will be a chaotic situation in countries if citizens start deciding when and who should be taking a second, third or fourth dose,” she added.

However, in Germany, a person is considered fully vaccinated if he or she has received two doses of the same vaccine or two types of vaccine. German Chancellor Angela Merkel, 66, helped pave the way for the recommendation for mixing vaccines. In June, Merkel received a second dose of Moderna's vaccine, after receiving the first dose from AstraZeneca.


Health authorities in a number of countries like Canada, Sweden, France, Spain and Italy, said people who have received the first dose of the AstraZeneca vaccine can get a second shot with another vaccine. In the UK, from the very beginning of the vaccination campaign, the government allowed mixing vaccines.

In South Korea, because the AstraZeneca vaccine was delivered late, the government announced that health workers who received the first dose of the AstraZeneca vaccine could get a second shot with Pfizer. In Canada, the vaccine advisory board said Pfizer and Moderna could be used interchangeably.

Currently, Bhutan, Bahrain, Indonesia, Thailand and the United Arab Emirates also allow vaccine mixing to improve the effectiveness of Covid-19 prevention.

Meanwhile, the US Food and Drug Administration is more cautious. According to this agency, people who have had their first dose of Pfizer or Moderna vaccine can get a second shot with another vaccine in exceptional cases, when the vaccines they got for the first shot are not available.

Phan Le - Nguyen Vinh

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