Home » Mixed Vaccination Questions and Answers – Fiona Russell

Mixed Vaccination Questions and Answers – Fiona Russell

by admin

June 16, 2021 5:31 pm

Given the continuous changes in the eligibility criteria for the AstraZeneca vaccine, the new variants of sars-cov-2 and the difficulties in providing doses, many are wondering if it is possible to “mix and match” (mix and match) vaccines against covid-19. That is, for example, if you can do the first dose with the AstraZeneca preparation and the second with the Pfizer-Biontech one, and then any boosters with other vaccines. While many studies are ongoing, data on this protocol already in use in Spain and the UK have recently been published.

The results are very promising and suggest that mixed vaccination programs can deliver higher antibody levels than those obtained from two doses of the same vaccine. So how does it work and why might so-called heterologous vaccination be a good idea?

What’s the benefit of mixing and matching?

Combining and matching vaccines would greatly increase flexibility.

Having a flexible immunization schedule allows you to better respond to the constraints of the global supply. If a vaccine is missing, instead of interrupting the entire course to wait for doses to be delivered, a different vaccine can be continued, regardless of which one was given as the first dose.

If one vaccine is less effective than another against a particular variant, the programs mix and match they could ensure that those who received the first dose of a low-efficacy vaccine can get a booster with a more effective product against the variant.

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Some countries are already adopting combined vaccination programs following the modification of the AstraZeneca vaccine recommendations due to a very rare side effect of severe thrombosis.

Several countries in Europe are now advising young people who previously received a first dose of this vaccine to get an alternative for the second dose, usually mRna vaccines such as Pfizer-Biontech.

Germany, France, Sweden, Norway and Denmark are among the countries that recommend mixed vaccination programs for this reason.

In a study carried out in the UK and published in The Lancet in May, 830 adults over the age of fifty were randomly selected to receive first one dose of Pfizer-Biontech or AstraZeneca and then the other.

It was observed that people who received mixed doses were more likely to experience mild to moderate side effects following the second dose of the vaccine (including chills, fatigue, fever, headache, joint pain, malaise, muscle aches and injection site pain) compared to the standard, non-blended program.

However, these reactions were short-lived and there were no other problems. Researchers have now delved into this study to see if regular preventive use of acetaminophen reduces the frequency of these reactions.

Another similar study (not yet peer-reviewed) carried out in Spain found that most of the side effects were mild or moderate and of short duration (two to three days). Furthermore, the side effects were similar to those resulting from taking two doses of the same vaccine.

The Spanish study found that people had a significantly higher antibody response 14 days after taking the Pfizer-Biontech booster after a first dose of AstraZeneca. These antibodies were able to recognize and inactivate sars-cov-2 in laboratory tests.

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This dose response of Pfizer-Biontech appears to be stronger than that which arose after receiving two doses of the AstraZeneca vaccine, according to data from previous studies. The immune response of a first dose of Pfizer-Biontech followed by AstraZeneca is not yet known, but the UK will have new results soon.

There is still no data on how effective the programs are mix and match in the prevention of covid-19. But they are likely to work well as the immune response is similar, or even better, to that found in studies using the same vaccine as first and second doses. So it is to be expected that they will work well in preventing the disease.

The results of these combined studies confirm that people who received the first dose of AstraZeneca can be vaccinated with a different booster if needed. Further studies are underway to evaluate matching programs with Moderna and Novavax vaccines.

(Translation by Stefania Mascetti)

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