If you ask medics and/or travel agents they will look up the fullest list(s) and tell you you must have them all - this because they want to cover themselves and/or have not the first idea as to what the actual risk is. Our GP just about reported me (to whom neither he or I would have known) for turning down immunisation involving a painful injection I had previously had into the thigh - for all of us including a two year old. The protection this would have offered was/is less than complete and then only for at most six months after which you need a repeat - we were going for years to Kenya. We went and none of us got ill except our elder son who suffered a ruptured appendix (a separate and quite different story).
I have previously explained on AB how I have dealt with malaria risk and was castigated for advocating suicidal behaviour. I have spent many years in malarial areas in Africa, the Middle East and Asia and only briefly (a few weeks) in the beginning took any pills. Importantly, no pills will give you 100% protection. I have never had malaria. What I have done is take fairly rigorous measures against being bitten by mosquitoes, nothing like all of which carry the parasite, with very good results (only bitten on very, very few occasions - two or three bites each on maybe a dozen occasions). This scheme has concentrated in particular on the accommodation I have occupied - spraying with a good pesticide (a brief squirt; Baygon is the best, where you can get it - use locally sourced stuff, UK bought is likely to be produced with UK health and safety attitudes, perfume etc. in mind) in upper corners of the space, under tables, beds, chairs, sofas and a strip around all opening windows and doors - repeat every 2-3 days or at most a week. Keep all windows and doors shut from onset of dusk until after dawn. Use a mosquito net if you are visiting and move between accommodation but still spray and on arrival/takeover in/of your room start with the internal spraying as above. When out and about from onset of dusk until after dawn, wear a good repellent on legs, arms, face and neck and any exposed areas. During the dusk-dawn period wear long trousers and long sleeves as a matter of preference.
I hope you enjoy your trip. If you get the chance of being in Nakuru Park very late in the day or else in the very early morning then look out for a leopard - that was where we had the only sighting of these very illusive animals apart from at a "bait" location in Samburu. Naivasha Lake is attractive but not as "wild" by feel as Nakuru Lake, in our experience.
If you truly worry about disease, get all the immunisations and take all the pills. Then if you ever feel at all unwell after your return home, go and see your doctor and tell him/her where you have been and when. This includes any cold/flu-like symptoms.