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01-10-2009 | Infectious disease | Article

Prenatal exposure to pandemic flu increases CVD risk


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MedWire News: People who are prenatally exposed to pandemic flu face a significantly increased risk for cardiovascular disease in later life, study results suggest.

The findings, published in the Journal of Developmental Origins of Health and Disease, emphasize the importance of influenza vaccination among pregnant women.

“The 1918–1919 influenza pandemic (Influenza A, H1N1 subtype) was notoriously virulent, causing symptomatic infections in one third of the USA across all ages and killing about 0.6% of the total population,” explain Caleb Finch (University of Southern California, Los Angeles, USA) and team.

They add: “If uncomplicated, the flu was a mild ‘3-day fever,’ with full recovery and low mortality. The lethality came from secondary bacterial infections that caused severe pneumonias, particularly among pregnant women.

“In addition, there are indications of long-term impairments in those exposed prenatally.”

To investigate further, the researchers studied data on 101,068 individuals who were born around the time of the 1918 influenza pandemic in the USA and who participated in the 1982–1996 National Health Interview Surveys.

They found that men born in the first 4 months of 1919, whose mothers were in the second or third trimester of pregnancy at the height of the epidemic, had a 23.1% higher risk for CVD after the age of 60 years than individuals of similar age who were not born during these months.

For women, those born in the first few months of 1919 did not have a significantly higher risk for CVD than other women of slightly younger or older age who were unlikely to have been exposed to pandemic flu. However, women born in the second quarter of 1919, whose mothers were in their first trimester at the height of the epidemic, were 17.0% more likely to have CVD than other women of similar age who were not exposed to the pandemic.

The researchers also examined height at World War II enrolment for 2.7 million men born between 1915 and 1922, and found that average height increased for every successive birth year except for the period coinciding with in utero exposure to the flu pandemic. Indeed, men who were prenatally exposed to H1N1 flu were slightly shorter than those born just a year before or a year later, even after controlling for known season-of-birth and maternal malnutrition.

The researchers conclude: “Prenatal exposure to the 1918 influenza pandemic was associated with at least a 20% excess risk for ischemic heart disease after the age of 60 years, as compared to birth cohorts with little or no prenatal exposure to influenza.”

They say that the findings “extend the hypothesized roles of inflammation and infections in CVD to prenatal infection by influenza.”

Finch added: “[The] 1918 flu was far more lethal than any since. Nonetheless, there is particular concern for the current swine flu which seems to target pregnant women. Prospective moms should reduce risk for influenza by vaccination.”

MedWire ( is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

By Mark Cowen

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