Japanese study examines efficacy and side effects of mixed vaccines Japanese study examines efficacy and side effects of mixed vaccines
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Japanese study examines efficacy and side effects of mixed vaccines

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    A study of medical workers

    Japan's health ministry has released its initial findings about the efficacy and side effects of booster shots from a different maker than initial vaccines. An ongoing study involves medical workers who were eligible for boosters from December 1, 2021.

    The subjects all received Pfizer shots for their two-dose primary vaccination. There were 2,826 people who received a Pfizer booster, and another 773 who had Moderna. Researchers analyzed antibody levels and side effects against the original, pre-mutation virus.

    Antibody levels

    Antibody levels were measured just before receiving the booster and compared with one month after the shot.

    The researchers chose subjects who had never developed antibodies from being infected with the virus. This was 396 people who had received a Pfizer booster, and 233 who had taken the Moderna version.

    The average antibody level for people with triple Pfizer increased 54.1-fold. For those who received Moderna as their third shot, the equivalent figure was 67.9.

    The findings tally with those of studies conducted overseas using the Omicron variant, which found that the Moderna booster was more effective than Pfizer.

    Antibody level a month after booster vaccine

    Side effects

    Side effects were also recorded. The sample size for this part of the study included 2,626 people who received a Pfizer booster, and 437 with Moderna.

    Occurrence frequency of side effects

    Symptoms were most likely to develop the following day. In most cases they subsided within two or three days. Among those who received a Pfizer booster, two cases of suspected inflamed heart muscle were reported, but neither was regarded as serious. None of the people who received a Moderna booster reported any such condition.

    Balancing efficacy and side effects

    Juntendo University School of Medicine Professor Ito Suminobu, who heads the research team, noted that the Moderna booster results in a higher antibody level, but also has an increased frequency of side effects compared to Pfizer. Among the study's subjects, there was no difference in the amount of sick leave taken between people who were boostered with either vaccine.

    This information is accurate as of February 25, 2022.

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