Table 3.

Weighing of the potential benefits against risks of harm from the inactivated influenza vaccine in pregnant women and young children.

Criteria	Pregnant women	Children aged 6 months to 5 years
Rationale for influenza vaccination	Risk of severe complications due to influenza infection	Risk of severe complications due to influenza infection, particularly in children less than 2 years of age High attack rates and the main source of influenza transmission High burden of influenza in low- and middle-income countries
Potential harm of inactivated influenza vaccine	Current literature does not suggest evidence of harm to the mother or fetus following inactivated influenza vaccine (IIV). Side effects, if any, are usually transient and minor.	Current literature does not suggest evidence of harm to the child following IIV. Side effects, if any, are usually transient and minor. In one study in China, IIV increased the risk of hospitalization in the 2015–2016 season, where a vaccine mismatch occurred (vaccine effectiveness: −63.7%; 95%CI = −423.6% to 48.9%, suggesting imprecise estimates)
Potential benefits of inactivated influenza vaccine	Moderate efficacy/effectiveness a of IIV against laboratory-confirmed influenza (range = 50%–70%) and influenza-related hospitalization (range = 45–65%) Passive mother-to-child immunity protecting newborns from influenza and influenza-related hospitalization following maternal IIV Newborns born to vaccinated mothers are less likely to be premature, small for gestational age, and of low birth weight when compared to those of unvaccinated mothers.	Moderate to high efficacy/effectiveness a of IIV against laboratory-confirmed influenza (range = 20%–90%) and influenza-related hospitalization (range = 43%–81% in those fully vaccinated) Preventing influenza transmission within the family and in the community
Acceptability to clinicians, pregnant women, and parents	Likely acceptable to pregnant women without contraindications, when shown appropriate risk-to-benefit ratio following influenza vaccination	Likely acceptable to children (parents/guardian) without contraindications, when shown appropriate risk-to-benefit ratio following influenza vaccination

^aDetermining exact IIV effectiveness estimates is challenging due to several factors, such as the IIV type (whole virus, virosome, split virus, or subunit) and manufacturing processes (eggs, cell culture, or recombinant DNA technologies) (31). Other confounding factors (31) are the vaccinee’s age, preexisting immunity, and comorbidities, as well as antigenic match/mismatches between the vaccine strains and circulating viruses and the use of adjuvants. Furthermore, the wide confidence intervals of the IIV effectiveness point estimates in most studies suggest imprecise knowledge.