Effectiveness of maternal vaccination with quadrivalent inactivated influenza vaccine in pregnant women and their infants in 2019-2020

Effectiveness of Influenza Vaccination During Pregnancy Against Laboratory-Confirmed Seasonal Influenza Among Infants Under 6 Months of Age in Ontario, Canada

BACKGROUND

Randomized trials conducted in low- and middle-income settings demonstrated efficacy of influenza vaccination during pregnancy against influenza infection among infants <6 months of age. However, vaccine effectiveness (VE) estimates from settings with different population characteristics and influenza seasonality remain limited.

METHODS

We conducted a test-negative study in Ontario, Canada. All influenza virus tests among infants <6 months from 2010 to 2019 were identified and linked with health databases to ascertain information on maternal-infant dyads. VE was estimated from the odds ratio for influenza vaccination during pregnancy among cases versus controls, computed using logistic regression with adjustment for potential confounders.

RESULTS

Among 23 806 infants tested for influenza, 1783 (7.5%) were positive and 1708 (7.2%) were born to mothers vaccinated against influenza during pregnancy. VE against laboratory-confirmed infant influenza infection was 64% (95% confidence interval [CI], 50%-74%). VE was similar by trimester of vaccination (first/second, 66% [95% CI, 40%-80%]; third, 63% [95% CI, 46%-74%]), infant age at testing (0 to <2 months, 63% [95% CI, 46%-75%]; 2 to <6 months, 64% [95% CI, 36%-79%]), and gestational age at birth (≥37 weeks, 64% [95% CI, 50%-75%]; < 37 weeks, 61% [95% CI, 4%-86%]). VE against influenza hospitalization was 67% (95% CI, 50%-78%).

CONCLUSIONS

Influenza vaccination during pregnancy offers effective protection to infants <6 months, for whom vaccines are not currently available.

Maternal vaccination-current status, challenges, and opportunities

AIM

Maternal vaccination is a promising strategy for protecting pregnant women and newborns against severe infections. This review aims to describe the current status and challenges associated with maternal vaccination against seasonal influenza, tetanus-diphtheria-pertussis (Tdap/DTaP), and novel coronavirus disease of 2019 (COVID-19) in Japan and other countries, mainly the United States and the United Kingdom.

METHODS

A literature search was conducted in PubMed and other public websites (e.g., Centers for Disease Control and Prevention) to obtain information on maternal vaccination.

RESULTS

Inactivated vaccines are recommended for pregnant women by gynecologic societies in Japan, the United States, and the United Kingdom. Among pregnant Japanese women, the influenza and COVID-19 (two doses) vaccine coverage rates were 27.0%-53.5% (six studies) and 73.6% (one study), respectively; there are no studies on maternal vaccination with DTaP. Concerns regarding vaccine safety are a major barrier to maternal vaccination across countries. Maternal vaccination is effective in preventing severe disease in pregnant women and protecting infants aged <6 months, is generally safe, and does not increase the risk of adverse maternal and fetal outcomes. Providing accurate information regarding vaccination through healthcare providers and the government and government funding for vaccines may help improve maternal vaccination rates in Japan.

CONCLUSION

Current coverage for maternal vaccination is still low globally mainly because of vaccine hesitancy among pregnant women. The government, drug-regulatory authorities, and healthcare professionals must educate pregnant women about the effectiveness and safety of maternal vaccines and encourage vaccination when the benefits outweigh the risks.

Vaccination with Deglycosylated Modified Hemagglutinin Broadly Protects against Influenza Virus Infection in Mice and Ferrets

Recent efforts have been directed toward the development of universal influenza vaccines inducing broadly neutralizing antibodies to conserved antigenic supersites of Hemagglutinin (HA). Although several studies raise the importance of glycosylation in HA antigen design, whether this theory can be widely confirmed remains unclear; which influenza HA with an altered glycosylation profile could impact the amplitude and focus of the host immune response. Here, we evaluated the characteristics and efficacy of deglycosylated modified HA proteins, including monoglycosylated HA (HA_mg), unglycosylated HA (HA_ug), and fully glycosylated HA (HA_fg), without treatment with H3N2 Wisconsin/67/2005. Our results showed that HA_ug could induce a cross-strain protective immune response in mice against both H3N2 and H7N9 subtypes with better antibody-dependent cellular cytotoxicity (ADCC) than the HA_mg- and HA_fg-immunized groups, which suggested that highly conserved epitopes that were masked by surface glycosylation may be exposed and thus promote the induction of broad antibodies that recognize the hidden epitopes. This strategy may also supplement the direction of deglycosylated modified HA for universal influenza vaccines.