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.

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.