"most badly affected" is correct and usable in written English.
You can use it when you want to emphasize how much severity of the impact of a negative event on a group or individual. For example: "The people of the coastal town were most badly affected by the hurricane."
Those most badly affected can all too easily be ignored.
Unions put real unemployment at over 18% with Greek youth being among the most badly affected.
This grouping includes the eight economies most badly affected by the collapse of 1997-98.
Among the most badly affected are those in wholesale and retail, real estate, education, health and social work.
I meet Lorna Reith, my local councillor whose ward covers half of the High Road most badly affected by the rioting, who is also responsible for children's services.
Reports from Nauru suggest she has severe burns to 70% of her body, with her upper body and face most badly affected.
"The other group feels that most people are not badly affected and that this disease progresses slowly".
Business has not been too badly affected because most of his customers are foreign tourists, but he has cut spending on everything but the basics, just in case the country does crash out of the euro.
The majority of respondents from Colombia were from the Andean city of Bogotá, which is not believed to have been badly affected, while most Venezuelan respondents were from the sweltering coastal capital Caracas, which is thought to have suffered high rates of infection.
If it remains at the lower end which the current hiatus in warming suggests is possible then most species should not be too badly affected.
He said that most of the men involved were badly affected by horrifying post-traumatic stress.
