Maternal Influenza Vaccination and the Risk of Laboratory-Confirmed Influenza Among Household Contacts Under the Age of Five in Mali.

Andrea G Buchwald,Boubou Tamboura,Fatoumata Diallo,Milagritos D Tapia,Moussa Doumbia,Fadima C Haidara,Karen Kotloff,Adama M Keita,Flanon Coulibaly,Sarah Boudova,Myron Levine,Samba O Sow

doi:10.4269/ajtmh.18-0450

Abstract

.Influenza transmission is increased among household contacts. Vaccination decreases transmission; however it is unclear how vaccinating a single individual alters disease risk among household contacts, particularly in regions with low vaccination coverage. Pregnant women were randomized to influenza or control vaccination. Households were visited weekly until infants born to enrolled women reached 6 months. Household contacts younger than 5 years were tested for laboratory-confirmed influenza (LCI). Incidence of LCI and rate ratios (RtR) comparing incidence between vaccine groups were calculated. The secondary infection rate (SIR) was calculated for households where LCI was detected. The H1N1 strain in the vaccine was a match for circulating H1N1 during the study, thus, all analyses were performed for H1N1-LCI and any LCI. A total of 5,345 household contacts younger than 5 years followed for a mean of 228 days (standard deviation [SD] = 45 days) experienced 2,957 influenza-like illness episodes. Incidence of any LCI and H1N1-LCI was 23 (N = 276) and 7.3 per 100,000 days (N = 89), respectively. Household contacts of women who received influenza vaccine had fewer LCI (RtR = 0.90; 95% CI: 0.71, 1.14) and fewer H1N1-LCI (RtR = 0.73; 95% CI: 0.48, 1.11) episodes than contacts in control households. Incidence of LCI and household SIR were low in households of women enrolled in an influenza vaccine trial in Mali. Although low incidence made statistical significance difficult to detect, there was a trend for decreased rates of H1N1-LCI in households where a pregnant mother received influenza vaccination.

Highlights

In 2008, there were approximately one million influenzaassociated severe acute lower respiratory infections among children under five worldwide; an estimated 180,000 cases occurred in Africa.[1,2] these estimates are based on severely limited surveillance data on influenza incidence in Africa, in sub-Saharan Africa
Household transmission is one of the primary contributors to the spread of influenza with approximately 42% of all infections estimated to occur in the household[5] and the risk of infection due to contact with an infected household member is estimated at 38%
Using data from a clinical trial of maternal influenza vaccination in Bamako, Mali, we aimed to examine the effect of vaccination of a single adult within the household on the risk of influenza among household contacts younger than 5 years, and the effect of vaccination on the household secondary infection rate (SIR)

Summary

Introduction

In 2008, there were approximately one million influenzaassociated severe acute lower respiratory infections among children under five worldwide; an estimated 180,000 cases occurred in Africa.[1,2] these estimates are based on severely limited surveillance data on influenza incidence in Africa, in sub-Saharan Africa. Household transmission is one of the primary contributors to the spread of influenza with approximately 42% of all infections estimated to occur in the household[5] and the risk of infection due to contact with an infected household member (secondary infection rate [SIR]) is estimated at 38%.6. Immunization against influenza protects the vaccinated individual from illness, the impact on household transmission is unclear. Few studies report significant protection when only a few individuals in the household are vaccinated, suggesting lower vaccine effectiveness against infection in the household setting.[6,7,10] Cocooning, or vaccinating adults to protect neonates in the household, has been

Objectives

Methods

Results

Conclusion