New CDC Study Identifies Timing of Seasonal Flu Epidemics for 25 Countries in Africa

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April 14, 2023 — A new CDC study published in the Lancet Global Health looked at 10 years of laboratory flu data from 25 African countries in order to provide new, policy-relevant information about when to expect annual flu epidemics. Understanding the timing of flu epidemics is essential for successful mitigation efforts such as vaccination campaigns and antiviral treatment messaging to clinicians. The findings of this study lay the foundation for timely public health interventions with the potential to reduce flu illnesses, hospitalizations, and deaths in these 25 African countries.

Study authors looked at data from 34 World Health Organization (WHO) member states on the African continent that report surveillance data to Global Influenza Surveillance and Response (GISRS) and used the 25 countries that had at least 3 years of consecutive surveillance data for their analysis. Those 25 African countries are home to 1.1 billion people or 89% of continent’s total population.

The authors applied three WHO-endorsed analytical methods to determine the start, peak, and end of seasonal flu activity for these countries and categorize flu epidemic patterns into five groups.

Six countries had a northern hemisphere pattern: Algeria, Burkina Faso, Egypt, Morocco, Niger, and Tunisia.
Eight countries had a primarily northern hemisphere pattern with some southern hemisphere epidemics: Cameroon, Ethiopia, Mali, Mozambique, Nigeria, Senegal, Tanzania, and Togo.
Three countries had a primarily southern hemisphere pattern with some northern hemisphere epidemics: Ghana, Kenya, and Uganda.
Three countries had a southern hemisphere pattern: Central African Republic, South Africa, and Zambia.
Five countries had no clear pattern: Côte d’Ivoire, Democratic Republic of Congo, Madagascar, Mauritius, and Rwanda.

Assessing the timing of flu activity in tropical countries has been challenging in the past because data were sparse in most WHO African countries, and annual epidemics may not have aligned with traditional northern (October-March) or southern (April-September) hemisphere epidemic patterns. However, the extent and quality of flu surveillance data reported by African countries to the GISRS FluNet network has improved substantially in the past decades, making the current analysis possible.

Based on these high-quality data, the study was able to identify and describe historical flu epidemics, characterize typical yearly activity, and explore optimal times for interventions. Additionally, identifiable flu epidemic periods can be used to recommend when to start vaccination campaigns with either the northern or southern hemisphere flu vaccine formulations, when to launch antiviral treatment messaging to clinicians, and similarly when to promote preventive measures such handwashing.

These findings further support the value of partnerships to enhance global flu surveillance. CDC works with a wide range of international partners, including the World Health Organization, National Ministries of Health, and others to build capacity to respond to pandemic flu and to prevent and control seasonal flu around the world. Additional information on how CDC participates in the Global Monitoring of flu is available.

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