Why do some countries mix and match vaccine doses?


KINIGUIDE | In a webinar on Tuesday, the Coordinating Minister of the National Covid-19 Vaccination Program (NIP), Khairy Jamaluddin, said Malaysia is considering offering the Pfizer-BioNTech vaccine to those who have received the AstraZeneca vaccine. as the first dose.

Not only that, but he also said it was “possible” for Malaysia to adopt this strategy, which appears to have received mixed reactions from netizens.

In this KiniGuide article, we take a look at the heterologous prime-boost vaccination strategy and why it is being studied.

What is the heterologous prime-boost?

Using the same vaccine multiple times to boost immunity is known as ‘homologous primary stimulation’ and is used in most vaccines, including those that protect against Covid-19.

However, the alternative strategy of using different vaccines for the first dose (priming dose) and subsequent doses (booster dose) has been explored for other diseases since at least 1992.

This is the heterologous prime-boost protocol, which appeared to elicit a more robust immune response, but which also increased the cost and complexity of vaccine development and deployment. The strategy had some early success in the vaccine to prevent Ebola.

To prevent Covid-19, the Sputnik V vaccine is designed from the outset as a heterologous prime-boost vaccine and has reported 91.6% efficacy in clinical trials.

The Sputnik V vaccine uses two different viruses – both rendered harmless – to provide temporary genetic instructions to human cells to produce a protein found outside of the virus that causes Covid-19.

The body’s immune system then recognizes these proteins as foreign objects and mounts the necessary immune response.

Sputnik V vaccine packaging is coded in red or blue to help differentiate the two doses.

With a few exceptions such as Sputnik V, however, most countries have not recommended heterologous primary stimulation against Covid-19 due to a lack of data to support its use. However, the situation is starting to change.

What did Khairy say about mixing the vaccine doses?

During online seminar Hosted by the Oxford & Cambridge Society of Malaysia, Khairy was asked whether the government plans to offer the Pfizer-BioNTech vaccine as a second dose to people who received the AstraZeneca vaccine as the first dose.

This is due to the poor performance of the AstraZeneca vaccine in preventing mild to moderate disease caused by the beta variant (B.1.351) of Covid-19, which is circulating in Malaysia.

In response, Khairy revealed that the Director of the Institute for Clinical Research (ICR), Dr P Kalairasu, had previously presented a paper on the matter to the Special Committee to Ensure Access to Covid-19 Vaccine Supply. (JKJAV) last week.

“We have real data that we received from Germany on heterologous vaccinations using AstraZeneca for the first dose and Pfizer for the second dose, which has been shown to stimulate neutralizing antibodies and be more effective against the variants …


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