A systematic review to understand the long-term mental health effects of influenza pandemics

Health effects of pandemics extend beyond morbidity and mortality from the disease itself and may include long-term mental health consequences. However, previous studies only consider narrowly defined populations at risk or examine pandemics caused by varied pathogens that may have inconsistent effects. We examine existing literature on these long-term mental health effects following one type of pandemic (influenza).

We conducted a systematic review of the long-term mental health effects of the 1889, 1918, 1957, 1968, and 2009 influenza pandemics. To our knowledge, this is the first review of studies of broad populations and multiple measures of mental health morbidity.

The literature search returned 8190 articles. After deduplication and title/abstract and full-text screening, 12 articles were reviewed. Seven articles focused on the 1918 pandemic and five on the 2009 pandemic. Study regions were USA or North America (n=5), Europe (n=3), and Asia (n=4). Long-term outcomes studied were suicide (n=4), admission to hospital or psychiatric facility (n=2), stress/anxiety/post-traumatic stress disorder (n=4) and schizophrenia and other/related conditions (n=2). The suggested mechanisms were infection (n=6), effects of non-pharmaceutical interventions (NPIs) (n=3), or other exposure pathways (n=3). Seven studies had a moderate risk of bias and five studies a high risk of bias.

Mental health effects have been an outcome of pandemics. Researchers should consider a variety of possible mechanisms, and that infection and restrictive NPIs may contribute to mental health morbidity. This study highlights the need for better understanding of the broader health, social, and demographic impacts of pandemics.