The effects of in-utero exposure to influenza on mental health and mortality risk throughout the life-course

Neuropsychiatric outcomes in offspring after fetal exposure to maternal influenza infection during pregnancy: A systematic review

Increasing evidence suggests that influenza infection in pregnancy may disrupt fetal neurodevelopment. The impact of maternal influenza infection on offspring neuropsychiatric health has not been comprehensively reviewed. We systematically reviewed comparative studies evaluating associations between maternal influenza infection and neuropsychiatric health outcomes in offspring. We searched MEDLINE, EMBASE, CINAHL, and Web of Science for articles published until January 7, 2022. Included were English studies evaluating neuropsychiatric outcomes in offspring aged > 6 months born to women with and without influenza during pregnancy, defined as clinical or laboratory-confirmed influenza illness, or being pregnant during pandemics/epidemics. Of 12,010 records screened, 42 studies were included. Heterogeneity in study design, exposures, and outcome definitions precluded meta-analyses. Four of 14 studies assessing schizophrenia reported adjusted ratio estimates from 0.5 to 8.2; most 95% CIs contained the null value; study quality was high in three of four. Two studies reported an increased risk of schizophrenia with influenza exposure any time during pregnancy (adjusted incidence rate ratio 8.2, 95% CI: 1.4-48.8; adjusted odds ratio 1.3, 95% CI: 1.2-1.5); another reported a reduced risk with first-trimester exposure (adjusted risk ratio 0.5, 95% CI: 0.3-0.9). Seven studies of autism spectrum disorder reported adjusted ratio estimates from 0.9 to 4.0; all 95% CIs included the null value; study quality was high in four. No conclusions could be drawn about the association between exposure to maternal influenza and neuropsychiatric outcomes due to the limited quantity and quality of available research. Large observational studies with long-term follow-up are required to investigate these associations.

Social distancing and influenza mortality in 1918 did not increase suicide rates in the United States

Recent research has suggested that the social distancing mandates introduced in the United States during the main waves of the 1918-20 influenza pandemic caused an increase in suicide rates. However, that finding relies on poor-quality, temporally mismatched data and has signs of omitted variable bias. Similarly, a long-standing finding that American suicide rates in 1918-20 were also boosted by the influenza mortality of the time has gone unquestioned in the literature, despite the original research admitting its risk of ecological fallacy. Using higher-powered mortality data, I cast doubt on both findings by analyzing the experiences of the pandemic in 43 of the largest American cities of the time. In line with some populations' experiences of COVID-19, I report tentative evidence that social distancing mandates during the 1918-20 pandemic may have been associated with decreased suicide rates. Larger, cross-national investigations of the effects of historical pandemics and social distancing mandates on mental health and suicide are needed.