"Background
... This study aims to urgently evaluate the effects of mRNA COVID-19 vaccination on COVID-19 infection rates and related behaviors among participants of the Yamato Project, which includes employees of Japanese small and medium-sized enterprises (SMEs)...
Results...
Vaccination status and COVID-19 infection
A higher percentage of participants who contracted COVID-19 had received at least one dose of the vaccine (51.3%) compared to those who did not contract the virus (39.0%) (p < 0.001). The odds of contracting COVID-19 were higher among vaccinated individuals compared to unvaccinated individuals...
Impact of number of vaccine doses
... Participants who received one to two doses had an adjusted OR of 1.63 (95% CI: 1.08-2.46, p = 0.020); those who received three to four doses had an adjusted OR of 2.04 (95% CI: 1.35-3.08, p = 0.001); and those who received five to seven doses had an adjusted OR of 2.21 (95% CI: 1.07-4.56, p = 0.033), indicating a higher reported risk of infection with an increasing number of doses."
@ Nakatani et al.
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