Safety, Immunogenicity, Efficacy and Effectiveness of Inactivated Influenza Vaccines in Healthy Pregnant Women and Children Under 5 Years: An Evidence-Based Clinical Review

Abstract

Annual influenza vaccination is often recommended for pregnant women and young children to reduce the risk of severe influenza. However, most studies investigating the safety, immunogenicity, and efficacy or effectiveness of influenza vaccines are conducted in healthy adults. In this evidence-based clinical review, we provide an update on the safety profile, immunogenicity, and efficacy/effectiveness of inactivated influenza vaccines (IIVs) in healthy pregnant women and children <5 years old. Six electronic databases were searched until May 27, 2021. We identified 3,731 articles, of which 93 met the eligibility criteria and were included. The IIVs were generally well tolerated in pregnant women and young children, with low frequencies of adverse events following IIV administration; however, continuous vaccine safety monitoring systems are necessary to detect rare adverse events. IIVs generated good antibody responses, and the seroprotection rates after IIVs were moderate to high in pregnant women (range = 65%–96%) and young children (range = 50%–100%), varying between the different influenza types/subtypes and seasons. Studies show vaccine efficacy/effectiveness values of 50%–70% in pregnant women and 20%–90% in young children against lab-confirmed influenza, although the efficacy/effectiveness depended on the study design, host factors, vaccine type, manufacturing practices, and the antigenic match/mismatch between the influenza vaccine strains and the circulating strains. Current evidence suggests that the benefits of IIVs far outweigh the potential risks and that IIVs should be recommended for pregnant women and young children.

Quadrivalent Vaccines for the Immunization of Adults against Influenza: A Systematic Review of Randomized Controlled Trials

“…Even if it is challenging to compare the immunogenicity and efficacy of different types of influenza vaccines [ 12 ], there are already reviews on this issue in pregnant women, children < 5 years old [ 13 ], and the elderly [ 14 ].…”

Influenza Viruses and Vaccines: The Role of Vaccine Effectiveness Studies for Evaluation of the Benefits of Influenza Vaccines

“…On the other hand, VE seems to be variable and suboptimal, with differences being related to the season, child’s age, antigenic match/mismatch, and the manufacturing process. In addition, since vaccination is recommended for children aged 6 months and older, a promising strategy may be maternal immunization [ 86 , 92 , 95 , 96 , 97 , 115 , 116 ].…”

Effects of Vaccination Against Influenza, Pertussis, and COVID-19 on Human Milk Antibodies: Current Evidence and Implications for Health Equity

“…There is year-to-year variability in vaccine efficacy, due to a number of factors including antigenic mismatch, pre-existing immunity, and the limited ability to predict the dominant viruses each year. However, the efficiency of the flu vaccines typically ranges between 50-70% in pregnancy but may be less for other populations ( 41 , 42 ).…”

“…There is year-to-year variability in vaccine efficacy, due to a number of factors including antigenic mismatch, preexisting immunity, and the limited ability to predict the dominant viruses each year. However, the efficiency of the flu vaccines typically ranges between 50-70% in pregnancy but may be less for other populations (41,42). Influenza vaccination during pregnancy leads to a 40% decreased risk of influenza-related hospitalization in pregnant women (43), as well as a significant increase in maternal and infant serum influenza IgG levels (44,45).…”