I was curious to see what O-sensei had to say about practice during a pandemic. I went back through the references I have available — and could not find that he said anything about pandemics in particular.
However, he would have been well-aware of the situation.
While Japan had experienced many waves of influenza in the past, it was devastated from 1918–1920 by three waves of the Spanish Influenza. A third of the population was sick and a half million people died – many of them once-healthy adults in the prime of life. Without doubt, O-sensei would have known many of them personally.
Even more grievous, O-sensei’s two young sons died in 1920, within three weeks of each other, of an “illness” — the records don’t seem to be more specific than that.
How did he respond?
At about this period, he was intensively practising sword technique, often by himself.
This was also approximately when he became deeply involved in the Omotokyo religion. He seemed driven to further his studies of spirituality.
I may be projecting, here, but I think he viewed the pandemic stoically — as something he could not change, but that could not change his own correct behaviour.
Here are some of his quotes related to Aikido and health, from “The Art of Peace” by John Stevens.
About maintaining practice: “Life is growth. If we stop growing, technically and spiritually, we are as good as dead.”
About personal health: “When I do Aikido, old age and illness vanish!”
About social distancing: “I do not need a dojo to practice Aikido. I’m not teaching for fame, status, or money. I can teach under a tree or on top of a rock. The entire world is my bridge to heaven.”
Lastly, COVID-19 is not the only lethal illness besetting us: “The Art of Peace is medicine for a sick world. We want to cure the world of the sickness of violence, malcontent, and discord—this is the Way of Harmony.”