Kathmandu offers the best-quality clinics and hospitals in Nepal, but these high standards at medical facilities decline the closer you get to the rural areas. In mountainous areas, there may be no health services at all. Trekkers who face health issues in the mountains are generally evacuated to Kathmandu, or even overseas if it happens to be a really serious condition. Always have your travel insurance with you to cover the costs of clinical treatment and emergency evacuations.
You do not legally require any vaccines to enter Nepal, unless you have come from an area where yellow fever is present – in that case, you must show proof of having been immunized. Your best choice is to seek medical advice at least six weeks before traveling, because some vaccinations require multiple injections over a period of time. Be aware that some vaccinations should not be given during pregnancy or to people with allergies.