Parents are being urged to check their children's immunisation status as they return to school and group activities with health authorities continuing to deal with an outbreak of whooping cough in the Nelson-Tasman and Marlborough regions.
Between October 28, 2017 and January 26, 2018 there have been 266 cases of pertussis notified in these regions.
Dr Stephen Bridgman from the Nelson Marlborough Public Health Service says the number of notified cases has decreased from its peak of about 50 a week before Christmas to 10 to 20 cases a week currently.
"It is possible that cases might increase again with the start of the school year," Dr Bridgman says.
An outbreak in 2011 to 12 continued with a "long tail" for several months.
"Children, and especially infants, remain at much higher risk than normal from this highly contagious, serious disease.
"If you are a parent, who has previously declined immunisation for your children, please urgently reconsider your choice and protect your children from contracting this serious, potentially fatal disease."
The highest rates have occurred among infants and school-aged children, while 15 cases have occurred in infants younger than 12 months.
The most cases occurred in early December.