Malaria is a major problem in Malawi - it's not uncommon for a child to suffer from the disease 4-5 times in a single year and it is one of the leading causes of mortality in children under 5. Although there are some effective preventive measures and treatments available, people must visit a clinic before they take advantage of them. Visiting a clinic can be expensive - the visit itself is free, but the wait can be as long as 8 hours to see a doctor, and if you have to wait that long that means missing out on a day of work.
One small problem with this campaign is that the notices are only in English. Although all Malawians learn English in school, it's certainly possible that these messages would reach more people if they were also presented in Chichewa, the dominant native language. Other than this small quibble, I think it's great that officials are using the World Cup as an opportunity to bring important public health messages to as many people as possible.