![]() Scientists speculate that, after the initial injection of the adenovirus-based vaccines, a person’s body develops an immune response to the adenovirus as well as the coronavirus spike protein. The AstraZeneca vaccine, Johnson & Johnson vaccine, and the Sputnik V vaccine each use a different kind of adenovirus. Researchers are particularly interested in seeing if mixed dosing regimens confer a better immune response for the vaccines that use a modified adenovirus to deliver instructions to the body’s cells to produce the spike protein. Scientists say this kind of mixing-and-matching is possible because most of the COVID-19 vaccines approved for use so far all elicit an immune response to the same part of the coronavirus: the spike protein. Separately, AstraZeneca is conducting a clinical trial to look at the effect of mixing doses of its vaccine with the Russian Sputnik V vaccine. These volunteers would receive either the AstraZeneca or Pfizer vaccine first, followed either by the same vaccine for their second dose, or a dose of either the Moderna or Novavax jabs. In April, scientists expanded the research to look at the Moderna and Novavax vaccines too, with a further 1,050 volunteers recruited. The initial study of the AstraZeneca and Pfizer vaccines involved more than 800 volunteers recruited across eight different sites in England. The British study is being carried out by the National Institute for Health Research. In the meantime, they said they had adapted the trials to study if offering volunteers the over-the-counter pain medication paracetamol (acetaminophen) reduced the side effects experienced with the second dose. Early days yetĭata on whether the mixed dosages produced a comparable or better immune response in those vaccinated is not yet available, the researchers said, adding that they “hope to report these data in the coming months.” The scientists also cautioned that the study only included people over the age of 50 and that it is possible that younger people might react differently. This could be an important consideration, especially when governments were vaccinating healthcare workers, according to Matthew Snape, a University of Oxford professor of paediatrics and vaccinology who is leading the mixed dose clinical trial. ![]() More frequent and pronounced reactions could lead to higher rates of absenteeism from work on the day after the second inoculation. The scientists said that none of these side effects were severe, describing them as “mild to moderate.” They also said the symptoms were short-lived, lasting at most a few days and that there had been no other safety concerns so far with mixing the Pfizer and AstraZeneca vaccines. ![]() ![]() These reactions included flu-like symptoms, such as fever, muscle aches, lethargy, and a general feeling of being unwell. government is sponsoring one of the earliest and largest clinical trials of this kind of mixing, which experts call “heterologous dosing.” And the very first preliminary results from that study are in: People who received the Pfizer vaccine followed by the AstraZeneca jab or vice versa, were more likely to experience uncomfortable reactions to the second dose than people who received two doses of the same vaccine, researchers at the University of Oxford reported in a research note published in the peer-reviewed medical journal The Lancet. Finally, if COVID-19 becomes endemic -as many experts think is likely- and people need frequent booster shots to retain immunity, then it is possible people will need to receive boosters of a different shot than they received initially. ![]()
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