Abstract
Pregnant women are increasingly considered a priority group for influenza vaccination, but the evidence in favor relies mainly on observational studies, subject to the “healthy-vaccinee bias”. Propensity score methods—sometimes applied—reduce but cannot eliminate residual confounding. Meta-analyses of observational studies show relative risks far from the thresholds that would confirm the efficacy of universal vaccination for pregnant women without needing randomized controlled trials (RCTs). Critical articles have shown that in the four RCTs investigating the outcomes of this vaccination, there was a tendency towards higher offspring mortality. In the largest RCT, there was a significant excess of presumed/serious neonatal infections, and also significantly more serious adverse events. Many widely acknowledged observational results (about hormone replacing therapy, vitamin D, omega-3 fatty acids, etc.) were confuted by RCTs. Therefore the international drive to consider this vaccination a “standard of care” is not justified yet. Moreover, there is the risk of precluding further independent RCTs for “ethical considerations”, so as “to not deny the benefits of influenza vaccinations to pregnant women of a control group”. Instead, before promoting national campaigns for universal vaccination in pregnancy, further large, independent, and reassuring RCTs are needed, even braving challenging a current paradigm. Until then, influenza vaccination should be offered to pregnant women only once open information is available about the safety uncertainties, to allow truly informed choices, and promoting also other protective behaviors.
Highlights
The WHO considers pregnant women the priority group for influenza vaccination [1], and there is global pressure to make it universal
A Cochrane review about influenza vaccination in healthy adults [2] found that the “NNV was in mothers and in infants”—resizing its effectiveness, the review continued: “The protective effect of vaccination in mothers and the newborn was very modest . . . smaller than the effect seen in other populations considered in this review
In the light of the Cochrane evidence-based conclusions, the WHO claim that pregnant women should be “the priority group for influenza vaccination” comes from an authoritative source, but does not seem adequately backed by evidence
Summary
The WHO considers pregnant women the priority group for influenza vaccination [1], and there is global pressure to make it universal. The objective of this perspective article is to present a novel viewpoint on the topic of influenza vaccination for pregnant women It presents original data as well as personal opinions, analyzing new observational evidence, seeking plausible alternative explanations for some favorable outcomes in the offspring of vaccinated pregnant women, and quantifying the limited benefits in their offspring in recent meta-analyzes of observational studies (pooling two trials at best). It adds some new evidence from the RCTs, to date, raising new questions about the safety of influenza vaccination during pregnancy. This perspective proposes some coherent implications of health policies
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