Sacha Westerbeek is one of the people trying to help some of the one million Sudanese people who have fled their homes in what the UN is calling "the world's worst humanitarian crisis".

She is working for the United Nations children's agency, Unicef, in Nyala, southern Darfur and is writing a diary for BBC News Online about her experiences.

Friday 30 July

The threat of a cholera outbreak is a reality in many of the camps for internally displaced people (ISP) and so the World Health Organization (WHO) has spearheaded a massive immunisation campaign.

The first phase in Kalma took place from 21 to 25 July, and the second phase will be carried out next week.

The state Ministry of Health (MoH), the non-governmental organisation Medecins du Monde and Unicef are helping to carry out the campaign.

Some immunisation points are at the Unicef-supported Children's Space Centre and in schools. Hundreds of children look curiously at what is happening. Cars drive in and out, and health workers and community volunteers mix water with strange-looking substances: sodium bicarbonate.

There is a team of local and international staff in each of the seven sectors, including two supervisors. The MoH supervisors train the community volunteers, who lead mobile "outreach" teams, to properly administer the vaccine. The teams go from shelter to shelter ensuring every person above the age of two receives their first dose of the vaccine.

The UN and NGO supervisors organise the logistics, such as preparation of vaccine carriers, and the delivery of water and other supplies such as plastic cups and a bottle of ink to mark the vaccinated person's finger.

I saw some of the 42,878 men, women and children receive their first dose of cholera vaccine. They were quite willing to take the medicine as they had been told it would prevent cholera. The children walk around proudly with their purple painted finger. It reminds me a bit of election time when your fingernail is coloured to show that you have cast your vote.

Wednesday 28 July

There are many extraordinary initiatives in the IDP camps and I have in particular a soft spot for the organisations that run primarily life-saving interventions.

For the people working in the therapeutic and supplementary feeding centres (TFC and SFC) there is no escape. Every single day, they are confronted with the daily suffering of many malnourished children. Some of the children are being brought in more dead then alive.

Some days ago I went to one of the Medecins Sans Frontieres feeding centres. The therapeutic day care centre is based in a row of tents. The women and children sit on mats. The heat is almost unbearable and the smell of "sickness" is all around. It is strange. Usually children make noise. Here, there is only some incidental moaning.

I see a woman with a very malnourished child in the corner. Her child seems to be in a very serious condition. I'm not a doctor, but being able to count a child's ribs is not a good thing.

Aisha, the mother, tries to comfort her son Abdulai by breastfeeding him, but she has nothing to give any more. Her breasts look like dry grapes and the milk is finished.

She arrived three months ago in Kalma IDP camp with her six children, but only came with her baby to the TFC some days ago.

She knew her son was becoming more malnourished by the day, but she had to help her pregnant daughter through a long and problematic labour. Her daughter gave birth and the baby is fine, but their money for food went on the hospital fees.

Aisha's daughter has still not recovered from her operation but has to look after her baby and four siblings while Aisha spends her days in the clinic. Abdulai has now been vaccinated for the common childhood diseases and received worm treatment. They could be attending the clinic for up to three months, receiving care and food to strengthen their immune systems.