Reconstructing the timing of South Africa’s influenza season over the past century from newspaper records

Abstract

While the contemporary influenza season in South Africa is understood, its historical occurrence and dynamics are not. This study applies methods in historical geography, using archival newspaper reports to reconstruct the historical influenza season in South Africa over the past century (1904–2019) to examine changes in the seasonality of influenza in South Africa, and to compare this to contemporary records. A 20% seasonal threshold was calculated and applied to the data to return this approximate 19-week season, with the start of the influenza season ranging from week one in 1917 to week 41 of the year in 1918. On average, over the past century, the South African influenza season has started in the first week of May and ended in the last week of August, lasting 19 weeks. This outcome aligns with the contemporary influenza season described in other studies. These records reveal considerable interannual variability in length and timing with no unimodal shifts. The most linked climate phenomenon to influenza transmission rate were cold and winter conditions. This has important implications in advancing the timing of influenza vaccines to the late summer and early autumn weeks. Moreover, this shows how archival newspaper proxy records can help us reconstruct the past.