Cumbria is facing a whooping cough "epidemic", health experts say.
Doctors have called for pregnant women and babies to be vaccinated after a recent surge in cases.
Nearly 200 cases have been identified in the county so far this year, NHS Cumbria said.
Nigel Calvert, associate director of public health for NHS Cumbria, warned it was "essential" children were immunised once they reached the appropriate age.
The Health Protection Service said more cases of whooping cough had been identified so far this year than for more than a decade.
NHS Cumbria said for maximum immunity, youngsters need jabs at two, three and four months before a pre-school booster at the age of three.
Pregnant women who get vaccinated can also protect unborn babies from developing the condition in the first few weeks after birth, NHS Cumbria added.
Whooping cough is highly contagious and usually begins with a persistent dry and irritating cough.
The infection can be treated with a course of antibiotics to prevent the infection spreading further but young infants may need hospital care.
Mr Calvert said: "All too often we've seen vaccinations delayed, perhaps because of holiday commitments, and babies remain vulnerable in that period.
"My message to parents is that they should make the vaccination of their children, at the right time, a priority."