Q:

How far can one go from Addis Ababa without needing prevention medication for Malaria?

I am travelling to Ethiopia and I was informed that you don't need medication regarding Malaria if you go to Addis Ababa. This is due to the fact that the city is above 2000mts where the mosquitos that spread it don't exist.
That was fine with me since I didn't have any plans to leave the capital. Meanwhile I will stay a few days longer and plans started imediately "popping". 
I read in this website that you are safe all around the highlands, since these are all in average higher than 2000Mts but is this good enough? how about if you go into a valley like where Blue Nile is (1800mts)?
How far can one go, and which directions, from Addis Ababa without prevention medication for Malaria?

A:

The NHS seems to think the entire country bar Addis Ababa is a high Malaria zone. 
The US State Department's website for Ethiopia under health states: 

Malaria is prevalent in Ethiopia outside of the highland areas excluding Addis Ababa. Extremely high malaria  transmission occurs throughout the year below 2,000 m (6,600 ft). Altitudes between 2,000 m and 2,500 m are subject to infrequent epidemics. Travelers who become ill with a fever or flu-like illness while traveling in a malaria-risk area and up to one year after returning home should seek prompt medical attention and report their travel history and anti-malarial medication taken. For additional information on malaria, insect precautions, protection from insect bites, and anti-malarial drugs, please visit the Centers for Disease Control and Prevention malaria website.

The link to the CDC on the state department is broken but a quick search of their website returned the following useful links.
CDC Malaria Map Application this application when launched states anything under 2500m excluding Addis Ababa is high.
CDC Malaria drug information,
CDC Malaria advice for travelers

A:

Some research papers suggest that Anopheles mosquitoes can be found quite high indeed, even above 2000 m above the sea so altitude does not appear to be the sole factor protecting Addis Ababa.
Official advice (e.g. from the CDC in the US or Institut Pasteur in France) indicates that malaria transmission happens throughout the country except in Addis Ababa and above 2500 m of altitude.
All this suggests that you can't assume any valley or rural area on the plateaus to be safe, even in the highlands (actual mountains above 3000 m should be OK).

A:

There is no malaria in Addis Ababa at all it is dry for the mosquito to survive. They need rather wet and dampy places. Also it is relatively colder than the other areas they seem to spread.In all the regions in the country where malaria may be found there are hotels with bed covers.  

