The standard of public healthcare in Nepal is mediocre at best. Avoid government hospitals if possible but few of them are quite ok. Makes sure your insurance covers the costs of private clinics, as these have relatively high standards and English-speaking doctors. The World Health Organization (WHO) recommends vaccinations against adult diphtheria, covid-19, and tetanus, Hepatitis A and B, and also typhoid. Malaria is not usually an issue in Kathmandu, but you may wish to consider taking precautions anyway.
Definitely take precautions if visiting any rural areas. Do not drink water that has not been boiled or purified in some other way. Be wary about how salads are washed and avoid ice unless you are certain the water is safe. Use boiled and filtered water for brushing teeth. This is less essential in the city’s better hotels. Some animals including the monkeys at Swyambhunath Temple may be carriers of rabies. Visit a clinic immediately if bitten, even if you have been vaccinated beforehand.