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Pregnant women at higher risk for flu-related hospitalization

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January 31, 2019

Pregnant women in any trimester, but not during the postpartum period, are at a higher risk for influenza-related hospitalization compared with nonpregnant women, according to study findings.

“Influenza A(H1N1)pdm09 has gone from a pandemic virus to a seasonal influenza virus since 2010, underscoring the importance of assessing the clinical impact of influenza viruses over time,” Namrata Prasad, MPH, epidemiologist and public health analyst at the Institute of Environmental Science and Research, and colleagues wrote.

For their study, Prasad and colleagues estimated influenza-associated hospitalization and outpatient visit rates by pregnancy, postpartum and trimester status using active surveillance data from the Southern Hemisphere Influenza and Vaccine Effectiveness Research and Surveillance (SHIVERS) project, as well as information collected at the administrative and individual level. The SHIVERS data come from predominantly urban areas in central, southern and eastern Auckland, Australia, and include women aged 15 to 45 years, Prasad and colleagues noted.

According to the study, between 2012 and 2015, there were 260 influenza-confirmed acute respiratory hospitalizations, with pregnant or postpartum women making up 17.7% of the cases. Additionally, there were 294 influenza-confirmed outpatient visits within the same time period, and 4.4% were pregnant or postpartum women. Overall, Prasad and colleagues observed that pregnant and postpartum women experienced higher rates of influenza hospitalization compared with non-pregnant women (rate ratio [RR] = 3.4; 95% CI, 2.5-4.7). The researchers observed similar results by trimester, with an RR of 2.5 in the first trimester (95% CI, 1.2-5.4), 3.9 in the second (95% CI, 2.4-6.3), 4.8 in the third (95% CI, 3-7.7) and 0.7 during the postpartum period (95% CI, 3-7.7).

pregnant woman recieving flu shot 
Pregnant women are at a higher risk for influenza-related hospitalization than nonpregnant women.
Source: Adobe Stock

Increased risk also was associated with influenza A viruses, with RRs of 5.3 for H1N1 (95% CI, 3.2-8.7) and 3 for A(H3N2) (95% CI, 1.8-5). However, an increased risk was not associated with influenza B, (RR = 1.8; 95% CI, 0.7-4.6).

Prasad and colleagues found that Mori women had significantly higher rates of influenza-related hospitalizations during pregnancy compared with women of European or “other” ethnicity (RR = 3.2; 95% CI, 1.3-8.4).

They noted that similar increased risks were not observed for influenza-confirmed outpatient visits. They also suggest pregnancy may be a risk factor for influenza and that effects of influenza type/subtype on disease risk among pregnant women should be monitored.

“We believe our findings have implications for antenatal health care and influenza vaccination providers,” Prasad and colleagues wrote. “Our findings from a robust, active, population-based surveillance study emphasize the importance of seasonal influenza vaccination among pregnant women and highlight the benefit of vaccination early in pregnancy.” – by Marley Ghizzone

Disclosures: The authors report no relevant financial disclosures.

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