The influenza pandemic referenced in this episode is based on the Russian Flu pandemic from 1889-1890, which recurred several times between 1891 and 1895. The virus started in the Russian Empire and spread mainly through travel via railway and by sea, and was the first pandemic to spread worldwide. Of the 300-900 million estimated cases, an estimated 13,000 Americans and approximately 1 million people worldwide were killed by the virus. A 2005 study stated that it might not have been an influenza virus, but the human coronavirus OC43; a 2020 Danish study reached a similar conclusion, and stated the symptoms of the 1889-1890 pandemic as very similar to those of Covid-19.