This makes some sense to me. By getting jabbed with needles as much as possible, we train our bodies to deal with a wide range of diseases, including ones it hasn’t seen yet.

How can a vaccine designed to protect against one disease be effective against a different disease?

Researchers think the vaccine trains the body to respond more quickly and more effectively to any pathogen it sees, Bruxvoort said…

One hypothesis is that different viruses have common characteristics that apply to all, said Dr. Lara Jehi, the Clinic’s chief research information officer and co-author of the Clinic-Brigham and Women’s study.

Cleveland.com

I remember reading about the BCG vaccine, which is a vaccine given to babies in tropical countries where tuberculosis is common. It leaves a scar, unfortunately, but I wonder if it could be part of the reason tropical countries in general seem to have been more resistant to the disease. Although I think another possible factor could be that people in tropical countries and poorer countries (which often go together) are just more used to and accepting of disease and their experience with Covid was not as thoroughly reported.