Sisi Ndebele, receives a seasonal influenza vaccine from a nurse at a local pharmacy clinic in Johannesburg, South Africa on Friday, April 24, 2020. Ordinarily, South Africa sees widespread influenza during the winter months, but this year almost none have been found — something unprecedented. School closures, limited public gatherings and calls to wear masks and wash hands have “knocked down the flu,” said Dr. Cheryl Cohen, head of the institute’s respiratory program.