Community Influenza Activity and Risk of Acute Influenza-like Illness Episodes among Healthy Unvaccinated Pregnant and Postpartum Women

Abstract

This study investigated the relation between weekly levels of influenza activity and the risk of acute influenza-like illness episodes among 8,323 healthy pregnant and postpartum women enrolled in a Puget Sound region, Washington, health maintenance organization, Group Health Cooperative, between June 1991 and December 1997. The authors classified weeks between October and May for isolate activity level based on surveillance data for influenza, respiratory syncytial virus, parainfluenza, and adenovirus infection. Influenza-like illness episodes were identified from medical encounters assigned a diagnostic code consistent with a symptomatic influenza infection. The authors compared the occurrence of influenza-like illness episodes within each pregnancy stage for periods with varying levels of influenza isolate detection in the community. Repeated-measures logistic regression methods accounted for time-dependent factors. The adjusted strength of association between influenza exposure and influenza-like illness episodes increased as the pregnancy stage progressed (first trimester odds ratio = 1.12, 95% confidence interval: 0.79, 1.59; second trimester odds ratio = 1.30, 95% confidence interval: 0.97, 1.73; third trimester odds ratio = 1.84, 95% confidence interval: 1.31, 2.59; postpartum period odds ratio = 2.28, 95% confidence interval: 1.42, 3.68). Pregnancy stage modified the association between influenza activity and influenza-like illness episodes. Findings estimate that 20-43 pregnant/postpartum women would need to be vaccinated with an 80% effective vaccine to prevent one influenza-like illness episode.

Influenza Vaccine Text Message Reminders for Urban, Low-Income Pregnant Women: A Randomized Controlled Trial

“…Importantly, pregnant women in the third trimester have been shown to be at higher risk than those in other trimesters to have an influenza-like illness episode. 29 These women also accounted for the majority of pregnant women with the severe 2009 H1N1 infection. 30 Of note, a recent study in low-income, primarily African American women did not demonstrate an effect of text messages on influenza vaccination in pregnant women, but only included women who were at less than 28 weeks gestational age at enrollment.…”

How and why researchers use the number needed to vaccinate to inform decision making—A systematic review

“…The disease outcomes reported were influenza in eight studies [4][5][6][7][8][9][10][11], tuberculosis in four studies [12][13][14][15], as well as three studies each of herpes zoster (HZ) [16][17][18], human papilloma virus (HPV) [19][20][21], and pertussis [22][23][24]. Two studies each focused on Hepatitis A [25,26] and pneumococcal disease [4,27].…”

“…Outcomes for which NNVs were measured included being a case of a specific disease, death, hospitalization, outpatient visit, qualityadjusted life year (QALY), disability-adjusted life year (DALY), and life-years lost. One third of the included studies (n = 9) used data from observational studies, which were primarily cohort studies [8][9][10]12,17,23,27,28,30]. In addition, seven studies were cost-effectiveness and economic analyses [4,5,13,15,16,21,22], six studies were systematic reviews [6,7,11,14,26,29]; three were commentaries [18,20,25], and two studies utilized mathematical modelling [19,24].…”

“…They estimated that 12-42 children 6-59 months of age need to be vaccinated to prevent one outpatient visit, and that vaccination was therefore an important means of reducing influenza associated outpatient visits in this age group. Similarly, two other studies used NNV to measure the benefits of influenza vaccination in preventing influenza and cases of influenza-like illness in pregnancy and postpartum women, and HIV-infected individuals, respectively [8,11]. Voordouw and colleagues investigated the benefit of influenza vaccination for preventing all-cause mortality.…”

Maternal immunization

“…17,18 Numerous studies have documented increased respiratory, febrile, and cardiopulmonary morbidity among pregnant women during seasonal influenza epidemics. 7,8,[19][20][21][22][23][24] These maternal consequences increasingly appear to be associated with numerous adverse pregnancy outcomes (preterm delivery, fetal distress, fetal growth restriction, cesarean delivery), and the potential for detrimental neonatal outcomes. 20,25,26 Influenza vaccination is the most effective strategy for influenza prevention during pregnancy.…”