The precautionary medical measures are being offered in stages to all those in school years seven to 13 who study or live in the Weymouth, Portland and Chickerell areas.
It said anyone attending Atlantic Academy, Kingston Maurward Academy and Coastland Academy would be invited for antibiotics and vaccination this week.
Anyone not in full-time education who would be in one of those year groups will also be able to have a single dose of antibiotics and the vaccine from Tuesday afternoon at All Saints Academy.
Young people aged under 16 should be accompanied by a parent or guardian who is able to provide consent.
The UKHSA said all those have already taken the preventative antibiotic which gives the most effective short-term protection will also be offered a meningitis B (MenB) vaccination.
It said more information on the vaccination schedule would be provided in due course.
The Dorset cases are the same sub-strain type, but a different sub-strain, to the one detected recently in Kent, and are not linked.
All three Weymouth students are said to be recovering well.