Year-Round Influenza Vaccination Improves Maternal, Fetal Outcomes

While the influenza vaccine is common in the United States, many other countries do not have access to the preventive treatment. In resource-challenged developing countries, influenza can present a significant challenge, especially among pregnant women.

A study published by The Lancet Infectious Diseases found that year-round flu vaccination of pregnant mothers in Nepal reduced infections by 30%. Additionally, vaccination increased birth weight by 15% and fewer infants had the infection.

Based on their findings, the authors project that year-round vaccination for pregnant mothers would benefit other tropical and subtropical parts of the world.

"The development of a child inside the mother affects that child its entire life, and low birth weight has lifelong health implications for a child," said corresponding study author Mark Steinhoff, MD. "The overall positive effect of performing these vaccinations -- which is not expensive -- is quite significant."

The authors focused their study on the subtropical terai plans of southern Nepal, which has high rates of malnutrition and limited healthcare access. The investigators visited villages in Nepal during routine health visits and followed up with the patients.

Included in the study were 3693 pregnant women aged 15 to 40 who were administered the flu vaccine or a placebo. Patients were randomized into 2 different cohorts.

Of the 2090 patients in the first cohort, 1040 patients received placebo, while 1049 received were administered the recommended trivalent inactivated vaccine. Of the 1603 patients in the second cohort, 805 received placebo and 798 received the vaccine.

Across both cohorts, the authors reported 3646 live births.

The investigators examined 3 primary outcomes: incidence of confirmed infant influenza 0 to 180 days after birth; incidence of low birth weight; and incidence of influenza-like illness in mothers 0 to 180 days post-partum, according to the study.

In the first cohort, influenza-like illness in patients who received the vaccine was reduced by 9% compared with placebo patients. In the second cohort, this illness was reduced by 36% in vaccinated patients. For both groups, the authors reported that vaccination reduced the rate of influenza-like illness by 19%.

The average rate of confirmed influenza infections was reduced by 16% among infants born to vaccinated mothers in the first cohort and 60% among infants born to vaccinated mothers in the second cohort compared with the placebo group. Low birth weight was reduced by 15% among infants born to vaccinated mothers in both cohorts.

The authors reported 111 infant deaths — 50 in the placebo group and 51 in the vaccination group – and 7 patient deaths – 5 in the placebo group and 2 in the vaccine group – during the study.

Overall, vaccination was observed to be beneficial to both mothers and infants in both cohorts.

Additional data are currently being gathered to conduct an expansion study in other similar regions where year-round influenza may be beneficial. Approximately 40% of the world’s population inhabits subtropical/tropical zones, but the flu vaccine is not widely used largely due to differing ideology.

The authors noted that the most positive results from the vaccine were observed in the second cohort. This group received 2 different formulations of flu vaccine that had a broader range of antigens to account for viral variability in Nepal, according to the study.

The variability of the influenza virus observed in the region requires improved vaccines that have broader coverage, the authors concluded.