What happens when COVID-19 meets other infectious diseases such as HIV/AIDS, tuberculosis, and malaria? Particularly in middle- and low-income countries, this is a relevant question. Nevertheless, multimorbidity, the coexistence of two or more health conditions, is in the field of infectious diseases also a growing challenge for high-income countries. What happens to the human body when it is affected by several infectious diseases? How can scientists advise politics and society on coping with the issue of COVID-19 and multimorbidity?