National seroepidemiological study of COVID-19 after the initial rollout of vaccines: Before and at the peak of the Omicron-dominant period in Japan

BACKGROUND: Based on routine surveillance data, Japan has been affected much less by COVID-19 compared with other countries. To validate this, we aimed to estimate SARS-CoV-2 seroprevalence and examine sociodemographic factors associated with cumulative infection in Japan. METHODS: A population-based serial cross-sectional seroepidemiological investigation was conducted in five prefectures in December 2021 (pre-Omicron) and February-March 2022 (Omicron [BA.1/BA.2]-peak). Anti-nucleocapsid and anti-spike antibodies were measured to detect infection-induced and vaccine/infection-induced antibodies, respectively. Logistic regression was used to identify associations between various factors and past infection. RESULTS: Among 16 296 participants (median age: 53 [43-64] years), overall prevalence of infection-induced antibodies was 2.2% (95% CI: 1.9-2.5%) in December 2021 and 3.5% (95% CI: 3.1-3.9%) in February-March 2022. Factors associated with past infection included those residing in urban prefectures (Tokyo: aOR 3.37 [95% CI: 2.31-4.91], Osaka: aOR 3.23 [95% CI: 2.17-4.80]), older age groups (60s: aOR 0.47 [95% CI 0.29-0.74], 70s: aOR 0.41 [95% CI 0.24-0.70]), being vaccinated (twice: aOR 0.41 [95% CI: 0.28-0.61], three times: aOR 0.21 [95% CI: 0.12-0.36]), individuals engaged in occupations such as long-term care workers (aOR: 3.13 [95% CI: 1.47-6.66]), childcare workers (aOR: 3.63 [95% CI: 1.60-8.24]), food service workers (aOR: 3.09 [95% CI: 1.50-6.35]), and history of household contact (aOR: 26.4 [95% CI: 20.0-34.8]) or non-household contact (aOR: 5.21 [95% CI:3.80-7.14]) in February-March 2022. Almost all vaccinated individuals (15 670/15 681) acquired binding antibodies with higher titers among booster dose recipients. CONCLUSIONS: Before Omicron, the cumulative burden was >10 times lower in Japan (2.2%) compared with the US (33%), the UK (25%), or global estimates (45%), but most developed antibodies owing to vaccination

抗原誘発性Th1・Th2サイトカイン産生に対する性ホルモンの影響の性差

The incidence, severity and prognosis of asthma can be affected by a number of factors, including the patient\u27s age and sex. Clinical observations and epidemiologic studies indicate that the prevalence and severity of asthma is higher among boys than girls, but that the ratio inverts after puberty. The reversal of the male/female prevalence of asthma at puberty strongly suggests a role of sex hormones. However, the mechanisms underlying the gender differences in the prevalence of asthma are not clear. Recently, we suggested that the sex differences were due to those in not only sex hormones but also lymphocyte functions based on findings in a murine model of allergic asthma. Therefore, we investigated the effect of sex hormones on antigen-induced cytokine production by lymphocytes to further investigate these gender differences. Splenocytes from ovalbumin (OVA)-sensitized female mice produced more IL-5, Th2 cytokine, than those from OVA-sensitized male mice, upon simulation with OVA. Progesterone decreased the production of IFN-g, Th1 cytokine, by splenocytes from both sensitized male and female mice. 17β-estradiol had no effect on Th1 and Th2 cytokine production by splenocytes from both mice. However, 5a-dihydrotestosterone decreased the production of Th2 cytokines by splenoytes from sensitized female mice but not these from male mice. Our findings suggest that lymphocytes from males and females have different sensitivities to sex hormones in antigen-induced cytokine production