None of the participants consulted an occupational health physician for treatment of adverse events after vaccination check details with either the pandemic H1N1 2009 vaccine or the seasonal trivalent vaccine. Most adverse events after vaccination with the pandemic
H1N1 2009 vaccine were mild and occurred on the day of, or the day after, the first and second vaccinations and most disappeared within three days. The frequency of local reactions was greater in Group 2 than in Group 1. One participant in Group 2 had erythema or swelling of ≥ 5 cm after the first dose of the pandemic H1N1 2009 vaccine, this resolved the following day. Local reactions in each arm of the participants after the simultaneous vaccination of the seasonal trivalent influenza vaccine and the pandemic H1N1 2009 vaccine were comparable. Local pain was evaluated on the basis of median VAS scores. Compared with male participants, female participants tended to have more severe pain at the injection site for all of the vaccination time points. The frequency of systemic reactions after the second vaccination of the
pandemic H1N1 2009 vaccine was also greater in Group 2. Fatigue occurred more frequently (13.6%) after the second pandemic H1N1 2009 vaccination compared with other vaccination time points. The major finding of this study is that antibody responses to the pandemic H1N1 2009 vaccine are inhibited by pre-vaccination with the seasonal trivalent
influenza vaccine. However, since no booster effect from vaccination with the second dose of the pandemic H1N1 BAY 80-6946 2009 influenza vaccine was observed in either study group, one vaccination may be enough to induce an adequate HI antibody response. Slight increases Edoxaban in GMT, SCR and SPR were observed after the second dose of the vaccine in Group 2, but these differences were not significant (GMT: P= 0.4902, SCR: P= 0.6875 and SPR: P= 0.4531). Because stratified randomization had ensured that the factors affecting the post-vaccination antibody response were well-balanced between the study groups, the results suggest that the antibody response to the second dose of the pandemic H1N1 2009 influenza vaccine was inhibited by the seasonal trivalent influenza vaccination. This result was unexpected because it was assumed that priming with the seasonal trivalent vaccine would expand the common memory to H1N1 viruses and facilitate the response to the subsequent pandemic H1N1 2009 vaccine. The inhibitory effect however was reminiscent of a peculiar immunological phenomenon seen in cases of natural infection with seasonal influenza viruses known as “original antigenic sin” in which an antibody response to a new variant is inhibited when individuals immunologically primed with other strains are re-infected with a related but different new variant. As to the mechanism of OAS, Kim et al.