The CDC is saying that based on past studies, the efficacy rate of a prior smallpox vaccine is 85%.
https://www.cdc.gov/poxvirus/monkeypox/clinicians/smallpox-vaccine.html
I have been vaccinated from smallpox and do not engage in the behaviors that appear to be the overwhelming source of monkeypox spread. Not to mention that so far, serious illness and death seem to be exceedingly rare. I am not going to spend a single second worrying about catching it on a cruise.
Of course, everyone is entitled to do what makes them feel comfortable, as long as you leave me alone. 🙂