Epidemiological study of influenza B in Shanghai during the 2009–2014 seasons: implications for influenza vaccination strategy

Abstract

A new quadrivalent influenza vaccine has been available for influenza B, which can pose a significant global health burden. Shanghai has the highest GDP and largest metropolitan population in China. To understand the impact of influenza B in Shanghai in terms of age-related incidence and relative prevalence compared with other subtypes, we conducted this retrospective epidemiological study of influenza B in the 2009-2014 seasons. A total of 71 354 outpatients with influenza-like illness were included, and both lineages of influenza B and subtypes of influenza A were identified using real-time RT-PCR. The antigenic characteristics of influenza B isolates were analysed by sequencing and reciprocal haemagglutinin inhibition assay. On average, 33.45% of influenza strains were influenza B, and 40.20% of strains isolated from children were influenza B. The incidence of influenza B was highest (12.52 per 100 people with influenza-like illness) in children ages 6-17 years and usually peaked in this age group at the early stage of an influenza B epidemic. Overall, both matched and mismatched influenza B strains co-circulated in Shanghai annually, and 44.57% of the circulating influenza B belonged to the opposite lineage of the vaccine strains. We concluded that influenza B has caused a substantial impact in Shanghai and that school-aged children play a key role in the transmission of influenza B. Hence, it may be beneficial to prioritize influenza vaccination for school-aged children to mitigate the outbreaks of influenza B.

Trends of influenza B during the 2010–2016 seasons in 2 regions of north and south Italy: The impact of the vaccine mismatch on influenza immunisation strategy

“…On the other hand, children and adolescents have been shown to be crucial in the spread of the virus in the community, experiencing some of the highest rates of influenza infection during seasonal epidemics 18,30 and, in this regard, it has been suggested that influenza B viruses could be transmitted with a higher reproductive number (R 0 ) in younger age population. 31 It is well known that influenza type B, when present as seasonal circulating virus within a geographic area, mainly occurs among younger persons than influenza A and school-aged children reflect the highest proportion of influenza B cases, 18,19,25,[32][33][34] as further confirmed in the present study among children aged 5-9 y.…”

“…In Shanghai, the age distribution of B infections documented between 2009 and 2014 was higher among young outpatients (6-17 years) seeking hospital medical care for ILI, 33 and similar findings were reported in a population study conducted in Southern China between 2009 and 2010. 35 Our results evidenced that ILI subjects infected by influenza B, in the context of the general population, were significantly younger than those admitted to hospital and an inverse correlation was found between the 2 healthcare settings, by comparison of age-stratified prevalences.…”

Understanding the complex seasonality of seasonal influenza A and B virus transmission: Evidence from six years of surveillance data in Shanghai, China

“…It is reasonable to assume that the extremely low activity level of influenza B in 2012/13 is the most likely explanation for this exception to the general pattern. This phenomenon was also found in other districts in Shanghai (Zhao et al, 2015) and in other provinces in China that year (Yang et al, 2018a,b).…”

Literature review of the epidemiology of influenza B disease in 15 countries in the Asia‐Pacific region

“…During the period from 2009 to 2012, B/Victoria lineage matching the seasonal influenza vaccines strain predominated over the B/Yamagata lineage. The proportion of B/Yamagata lineage exceeded 97% of all circulating influenza B viruses in late 2012 and resulted in complete vaccine B strain mismatch …”