Some background on seasonal mortality, relevant to the measurement of excess Covid mortality in the Southern Hemisphere. A brief thread, with pictures. (1/7)

Mortality is generally seasonal – more deaths in winter than summer. A significant component (but by no means all) of that mortality is flu-related. The Covid outbreak in the Southern Hemisphere coincides with the peak flu season. (2/7)

With so few cases of flu being reported, a winter spike in deaths in these countries is almost certainly not flu-related. (7/7)

And yet, it would appear (using data from the WHO: https://www.who.int/influenza/gisrs_laboratory/flunet/en/) that the virtual cessation of international travel and lockdowns has hugely attenuated the flu season in the Southern Hemisphere: (3/7)

Southern Hemisphere (last 12 months). Almost no cases since week 16 (13 April on), and certainly nothing like the previous year (4/7)

Australia: Big flu season in 2019. Ditto: New Zealand. Ditto South Africa which experienced an atypical outbreak in early March (5/7).

Brazil (stops abruptly at week 19 after the start of a season (one or two cases reported in July)). And Chile. (6/7)