Perinatal Outcomes of Asynchronous Influenza Vaccination, Ceará, Brazil, 2013-2018

Abstract

In Ceará, Brazil, seasonal influenza transmission begins before national annual vaccination campaigns commence. To assess the perinatal consequences of this misalignment, we tracked severe acute respiratory infection (SARI), influenza, and influenza immunizations during 2013-2018. Among 3,297 SARI cases, 145 (4.4%) occurred in pregnant women. Statewide vaccination coverage was >80%; however, national vaccination campaigns began during or after peak influenza season. Thirty to forty weeks after peak influenza season, birthweights decreased by 40 g, and rates of prematurity increased from 10.7% to 15.5%. We identified 61 children born to mothers with SARI during pregnancy; they weighed 10% less at birth and were more likely to be premature than 122 newborn controls. Mistiming of influenza vaccination campaigns adversely effects perinatal outcomes in Ceará. Because Ceará is the presumptive starting point for north-to-south seasonal influenza transmission in Brazil, earlier national immunization campaigns would provide greater protection for pregnant women and their fetuses in Ceará and beyond.

Keywords: Brazil; childbirth; influenza; influenza viruses; pregnancy; premature birth; respiratory infections; severe acute respiratory infection; severe flu syndrome; underweight; vaccination; vaccines; viruses.

Figure 1

Seasonal patterns in rainfall and influenza and timing of influenza vaccination campaign, Ceará, Brazil, 2018. A) Location of Ceará state in the semiarid region of Brazil. B) Monthly rainfall in Ceará. Numbers indicate total influenza cases each month. C) Weekly influenza cases before, during, and after the annual vaccination campaign in Ceará.

Figure 2

Design of study of SARI during pregnancy, Ceará, Brazil, 2013–2018. SARI, severe acute respiratory infection; SINASC, the Sistema de Informações Sobre Nascidos Vivos (24); SINAN, Notifiable Diseases Information System (19).

Figure 3

Patterns of influenza and severe acute respiratory infections and timing of influenza vaccination campaigns, Ceará, Brazil, 2013–2018. A) Dominance of various influenza subtypes over time. Years indicate date each strain was first identified. B) Weekly cases of influenza and severe acute respiratory infections.

Figure 4

Associations between SARI among pregnant women and birth outcomes, Ceará, Brazil, 2018. A) By birthweight; B) by gestational score. Gestational length scored using a 1–6 scale in which 1 indicates <22 weeks, 2 indicates 22–27 weeks, 3 indicates 28–31 weeks, 4 indicates 32–36 weeks, 5 indicates 37–41 weeks, and 6 indicates >42 weeks of gestation. SARI, severe acute respiratory infection.

Figure 5

Seasonal periodicity of gestational score (A) and birthweight (B), Ceará, Brazil, 2013–2018. Gestational length scored using a scale of 1–6: 1 indicates <22 weeks, 2 indicates 22–27 weeks, 3 indicates 28–31 weeks, 4 indicates 32–36 weeks, 5 indicates 37–41 weeks, and 6 indicates >42 weeks of gestation.

Figure 6

Comparison of birthweights of children born to mothers who did (cases) and did not (controls) have severe acute respiratory infections during pregnancy, Ceará, Brazil, 2013–2018. Horizontal lines within boxes indicate means; box tops and bottoms indicate 25th and 75th percentiles; whiskers indicate 95% CIs. p = 0.02 by Mann-Whitney test.