Global influenza seasonality to inform country-level vaccine programs: An analysis of WHO FluNet influenza surveillance data between 2011 and 2016

<div><p>By analyzing publicly available surveillance data from 2011–2016, we produced country-specific estimates of seasonal influenza activity for 118 countries in the six World Health Organization regions. Overall, the average country influenza activity period was 4.7 months. Our analysis characterized 100 countries (85%) with one influenza peak season, 13 (11%) with two influenza peak seasons, and five (4%) with year-round influenza activity. Surveillance data were limited for many countries. These data provide national estimates of influenza activity, which may guide planning for influenza vaccination implementation, program timing and duration, and policy development.</p></div

Illustrative examples of influenza seasonality classifications, 2011–2016.

<p>Illustrative examples of influenza seasonality classifications, 2011–2016.</p

Global maps of monthly influenza activity, 2011–2016.

<p>Global maps of monthly influenza activity, 2011–2016.</p

Influenza activity¹ seasonality by World Health Organization region, 2011–2016.

<p>Influenza activity<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0193263#t001fn001" target="_blank">¹</a> seasonality by World Health Organization region, 2011–2016.</p

Forecasting demand for maternal influenza immunization in low- and lower-middle-income countries

<div><p>Immunization of pregnant women against seasonal influenza remains limited in low- and lower-middle-income countries despite being recommended by the World Health Organization (WHO). The WHO/PATH Maternal Influenza Immunization Project was created to identify and address obstacles to delivering influenza vaccines to pregnant women in low resource setting. To gain a better understanding of potential demand from this target group, we developed a model simulating pregnant women populations eligible for vaccination during antenatal care (ANC) services in all low- and lower-middle-income countries. We assessed potential vaccine demand in the context of both seasonal and year-round vaccination strategies and identified the ways that immunization programs may be affected by availability gaps in supply linked to current vaccine production cycles and shelf life duration. Results of our analysis, which includes 54 eligible countries in 2015 for New Vaccine Support from Gavi, the Vaccine Alliance, suggest the demand for influenza vaccines could be 7.7 to 16.0 million doses in 2020, and 27.0 to 61.7 million doses by 2029. If current trends in production capacity and actual production of seasonal influenza vaccines were to continue, global vaccine supply would be sufficient to meet this additional demand—although a majority of countries would face implementation issues linked to timing of supply.</p></div

Model schematic (base case scenario).

<p>Model schematic (base case scenario).</p

Countries eligible for New Vaccine Support (NVS) from Gavi in 2015 at risk of facing an availability gap of influenza vaccine formulations.

<p>Countries eligible for New Vaccine Support (NVS) from Gavi in 2015 at risk of facing an availability gap of influenza vaccine formulations.</p

Seasonality and potential gap in availability of Northern and Southern Hemisphere formulations.

<p>Seasonality and potential gap in availability of Northern and Southern Hemisphere formulations.</p

Comparison of demand estimates generated under base case scenario versus alternative scenarios (millions of doses).

<p>Comparison of demand estimates generated under base case scenario versus alternative scenarios (millions of doses).</p

Influenza Pneumonia Surveillance among Hospitalized Adults May Underestimate the Burden of Severe Influenza Disease

<div><p>Background</p><p>Studies seeking to estimate the burden of influenza among hospitalized adults often use case definitions that require presence of pneumonia. The goal of this study was to assess the extent to which restricting influenza testing to adults hospitalized with pneumonia could underestimate the total burden of hospitalized influenza disease.</p><p>Methods</p><p>We conducted a modelling study using the complete State Inpatient Databases from Arizona, California, and Washington and regional influenza surveillance data acquired from CDC from January 2003 through March 2009. The exposures of interest were positive laboratory tests for influenza A (H1N1), influenza A (H3N2), and influenza B from two contiguous US Federal Regions encompassing the study area. We identified the two outcomes of interest by ICD-9-CM code: respiratory and circulatory hospitalizations, as well as critical illness hospitalizations (acute respiratory failure, severe sepsis, and in-hospital death). We linked the hospitalization datasets with the virus surveillance datasets by geographic region and month of hospitalization. We used negative binomial regression models to estimate the number of influenza-associated events for the outcomes of interest. We sub-categorized these events to include all outcomes with or without pneumonia diagnosis codes.</p><p>Results</p><p>We estimated that there were 80,834 (95% CI 29,214–174,033) influenza-associated respiratory and circulatory hospitalizations and 26,760 (95% CI 14,541–47,464) influenza-associated critical illness hospitalizations. When a pneumonia diagnosis was excluded, the estimated number of influenza-associated respiratory and circulatory hospitalizations was 24,816 (95% CI 6,342–92,624). The estimated number of influenza-associated critical illness hospitalizations was 8,213 (95% CI 3,764–20,799). Around 30% of both influenza-associated respiratory and circulatory hospitalizations, as well as influenza-associated critical illness hospitalizations did not have pneumonia diagnosis codes.</p><p>Conclusions</p><p>Surveillance studies which only consider hospitalizations that include a diagnosis of pneumonia may underestimate the total burden of influenza hospitalizations.</p></div