Mixing Covid-19 vaccines and reactogenicity

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  Mixing Covid-19 vaccines and reactogenicity

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1. The story: Researchers at the University of Oxford launched "Com-COV Study", to investigate effects of alternate doses of Pfizer-BioNTech vaccine and Oxford-Astra Zeneca vaccine. The researchers concluded that mixing the administration of these doses in a more frequent mild to moderate reactions will increase the reactogenicity of the vaccine.
2. Lessons: If the doses of Pfizer-Biotech and Oxford-AstraZeneca are administered at a four-week interval, one after the other, the reactogenicity of the vaccine increases.
3. Reactogenicity: The "reactogenicity" of the vaccines refer to the property of the vaccine to produce expected adverse reactions. This may be fever, redness or soreness or swelling at the site of the jab.
4. Inferences: Mixing doses might increase work absences the day after immunisation. Accordingly, at least 10% of the participants who got mixed doses reported severe fatigue as compared to that of 3% of those who were inoculated with one dose.
5. Why vaccine mixing: As there were vaccine shortages all over the world and supply chain issues, the scientists explored the idea of mixing and matching vaccines. Situations such as rare blood clots in Johnson and Johnson vaccines and Astra Zeneca vaccines are forcing people to have second thoughts of taking their second doses. They are therefore shifting to some other vaccine after taking the first dose of these.

• Researchers believe that the mixing is done with the vaccines that share the same target. For instance, Pfizer-BioNTech and AstraZeneca target spike protein. Some believe that the efficiency of the vaccines increase when they are mixed up. 
• This is because, two different vaccines are created based on two different methods. For instance, AstraZeneca uses Adeno virus found in Chimpanzees and on the other hand Pfizer mRNA vaccine delivers genetic instructions human cells. It directs them to make spike proteins and then teaches the human cells to kill them.
• The mixed vaccine is called heterologous boost.  

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