TWiV explains why the concept of herd immunity might not apply to COVID-19, and the observation that smallpox vaccination causes an increase in skin bacteria that promote pathology and influence the immune response.

TWiV reviews the vials labeled smallpox that were not, re-emergence of enterovirus D68 in Europe, efficacy of inactivated SARS-CoV-2 vaccine, and cellular correlates of protection for an oral influenza virus vaccine.

Rich reviews the history of smallpox and the discovery of variola viral genomes in ancient DNA from human remains throughout Northern Europe, which pushes back the earliest date of smallpox virus infection to ~600–1050 CE, overlapping the Viking Age.

Donald “D.A.” Henderson, a physician, educator, and epidemiologist who led the World Health Organization’s campaign to eradicate smallpox, died at 87 years of age on Aug. 19, 2016. Vincent was fortunate to have the opportunity to speak with DA Henderson in 2014 about his career, the smallpox eradication effort, and what it means for the eradication of polio.