Exposure to ultrafine particles during pregnancy enhances the risk of respiratory viral infection, according to a new study published in Particle and Fibre Toxicology

“We know that air pollution affects the pulmonary immune system, making individuals more susceptible to viral infections,” says Natalie Johnson, PhD, associate professor in the Texas A&M University School of Public Health’s Department of Environmental and Occupational Health, who led the study, in a release. “We also know pregnant women are already at increased risk for severe flu. Surprisingly, studies have not interrogated the combined effects of pregnancy, air pollution, and influenza. Our findings demonstrate the need to further study these interactions in order to prevent short- and perhaps long-term impacts on maternal health.”

In the study, Johnson and co-authors point out that there are several physiological characteristics that explain maternal susceptibility to viral infection. Among those are increased cardiac output and decreased tidal volume—the amount of air that moves in or out of the lungs with each respiratory cycle—as well as immunological changes such as selective modulation of immune cell subsets to protect the developing fetus.

The research team also highlights that vaccination compliance during pregnancy is generally below 50%, despite vaccination against influenza being safe and effective, leading to increased risk of developing respiratory infection. They further note that pregnant women are disproportionately affected by influenza, resulting in a more than 10-fold increase in hospitalization risk.

As a result, air pollution, a worldwide environmental health issue, is responsible for one in nine deaths with an annual premature mortality of more than 7 million. A mixture of gases and tiny airborne particulate matter, categorized as ultrafine particles, are critical to recognize and identify, especially to protect vulnerable populations, according to researchers.

The research team says these findings support future clinical and regulatory interventions for protecting pregnant women and controlling ultrafine particles. According to the researchers, it is imperative that pregnant women in urban cities, where influenza and ultrafine particles are more prevalent, are provided vaccinations and preventive measures limiting exposure to ultrafine particles to protect maternal health.

“Air pollution is a pervasive environmental health issue,” says Johnson in the release. “Strategies to protect the most vulnerable, like pregnant women, are of high priority to decrease adverse health effects.”