The CDC warns that compared with nonpregnant women of similar reproductive age, pregnant women and their unborn babies are at increased risk for influenza-related complications, including hospitalizations and death. Despite these complications, pregnant women often still have concerns about the safety of the influenza vaccine and its effect on their unborn child. A recent analysis of data from a global quadrivalent influenza vaccine pregnancy registry offers reassuring results.

A descriptive report from the pregnancy registry for the quadrivalent inactivated influenza vaccine (IIV4; Fluzone) reviewed vaccine exposures during pregnancy and relevant outcomes in both mother and child. Information from nine countries was included in this analysis, which captured data from 239 IIV4 pregnancy exposures resulting in an adverse event (AE) that occurred between August 2013 and September 2019.

In this report, vaccine exposure was defined as receiving the IIV4 vaccine during pregnancy or within 30 days of the last menstrual period.

Prospective exposures included those reports that were made following vaccine exposure but before knowledge of the pregnancy outcome was known through prenatal testing. Retrospective exposure occurred when prenatal tests had already been undertaken before the exposure was reported.

Exposures were further divided into maternal outcomes (i.e., impacting maternal health but independent of the pregnancy), pregnancy and obstetrical outcomes (POOs; i.e., those directly affecting pregnancy, labor or delivery), and neonatal outcomes (i.e., those directly related to the infant at birth or within the first 29 days of life).

Of the 239 AE reports of exposure to IIV4, 210 were prospective and 29 were retrospective. Not all exposures had evaluable follow-up. In the case of maternal outcomes, all exposures were included regardless of the availability of follow-up information. POOs had to have at least one successful follow-up. For neonatal outcomes, all cases had to have follow-up information.

Based on prospective exposure reports, there were 105 maternal AEs occurring in 50 pregnant women and 10 maternal AEs based on retrospective reports. These mostly included administration of expired or extra vaccine, pain at the injection site, cough, fatigue, or headache.

There were 62 prospective and 29 retrospective POOs with at least one follow-up. Among these were four spontaneous abortions, one case of fetal hypokinesis, two cases of morning sickness, four cases of gestational diabetes, and one case each of abnormal fetal heart rate, severe premature separation of the placenta, placenta previa, and fetal tachycardia.

There were 15 prospective and 29 retrospective reports of neonatal outcomes, which included one premature birth, four cases of tallipes (club foot), and one case each of an atrial septal defect and congenital central nervous system anomaly.

Of the 210 prospective reports, 148 were lost to follow-up. Of the remaining cases, there were 62 with known POOs. Of these 62 cases, 43 exposures were lost to further follow-up, four involved a spontaneous abortion, and 15 were associated with a known neonatal outcome.

Among the 29 retrospective reports, there were 29 known POOs. Further follow-up revealed one fetal death and 28 exposures with known neonatal outcomes.  

Only 30 AEs reported in 19 women were considered serious, and these included hypovolemic shock, vaccine failure, Guillain-Barre syndrome, and tonic-clonic seizures in a patient with a seizure history.

It is important to note that due to the voluntary and often incomplete nature of reporting to this database, causality cannot be established between an AE and IIV4.

The investigators concluded that their findings did not indicate any new safety concerns for IIV4.

This data analysis lends support to pharmacists' recommendations that pregnant women should be vaccinated against influenza and can be used to help dismiss any concerns that pregnant women may have about receiving the influenza vaccine.

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.

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