Incidence of influenza and other respiratory viruses among pregnant women: A multi-country, multiyear cohort.

Objective: To quantify rates of influenza illness and assess value of influenza vaccination among pregnant women in Panama and El Salvador.

Methods: Pregnant women were enrolled and followed each week in a prospective cohort study to identify acute respiratory illnesses (ARI). Nasopharyngeal swabs obtained from women with febrile ARI were tested by reverse-transcription polymerase chain reaction for influenza and other respiratory viruses.

Results: We enrolled 2556 women between October 2014 and April 2017. Sixteen percent developed at least one ARI; 59 had two ARI, and five had three ARI for a total of 463 ARI. Women in El Salvador and Panama contributed 297 person-years (py) and 293 py, respectively, during influenza circulation. Twenty-one (11%) of 196 sampled women tested positive for influenza. Influenza incidence was 5.0/100 py (5.7/100 py in El Salvador and 4.3/100 py in Panama). Only 13% of women in El Salvador and 43% in Panama had been vaccinated against influenza before influenza epidemics (P < 0.0001).

Conclusions: One in six pregnant women developed ARI and more than one in ten ARI were attributable to vaccine-preventable influenza. While women were at risk of influenza, few had been vaccinated before each epidemic. Such findings suggest the utility of evaluations to optimize vaccine timing and coverage.