The useful question
The CDC documents three waves of influenza in 1918–19. The WHO characterized COVID-19 as a pandemic on 11 March 2020. The useful resemblance lies in watching spread, health-system response and changing conditions over time, rather than in the shared label of pandemic.
What changes
In 1918, rapid virus identification, specific vaccination, intensive care and immediate global data exchange did not exist as they do now. The pathogens differ. The number of waves in 1918 cannot predict the timing or severity of another outbreak.
What to observe
Spread, hospitalizations, health-system capacity and surveillance quality can frame analysis of a respiratory emergency. This is an editorial reading framework, not a clinical model or estimate of individual risk.