In this age group, RSV can cause bronchiolitis (inflammation of the small breathing tubes of the lung) and pneumonia (infection of the lung).
The virus is particularly contagious, with a person typically infectious for around 10 days after showing symptoms.
The virus spreads via droplets, predominantly from sneezing or coughing.
In Whanganui, the DHB has set up designated isolation rooms, where children are placed inside rooms with droplet precautions.
All staff caring for RSV-infected patients have to wear PPE to ensure the virus doesn't spread within the hospital.
The DHB has also taken the rare step of asking all children not to visit the hospital, and adult visitors are asked to keep their visits to a minimum.
A Whanganui DHB spokesman told the Chronicle that although there was a decline in admissions during the recent school holidays, there had been a steady admission rate since, and the DHB urged parents to remain vigilant.
"Simple hygiene measures such as keeping children at home, washing hands, coughing and sneezing into your elbow and not sharing drinking cups and glasses can help stop RSV from spreading," the spokesman said.
"If a child has RSV symptoms – runny nose, cough, vomiting or fever – parents should phone Healthline on 0800 611 116 or talk to their GP. However, if symptoms persist or get worse they should be brought to Whanganui Hospital's emergency department."
What is RSV?
• Respiratory syncytial virus (RSV) causes infections of the lungs and respiratory tract.
• It's so common that most children have been infected with the virus by age 2, but it can also infect adults.
• Symptoms are usually mild and typically mimic a common cold but they cause a severe infection in babies - especially premature infants - and elderly or those with weak immune systems.
Advice for self-management of colds
• Get plenty of rest.
• Drink lots of fluids such as water.
• Use a humidifier to increase air moisture, especially in your bedroom.
• No medicines cure a cold. Antibiotics only work against bacterial infections, not the viral infections that cause a cold.
• Symptoms can be treated with medicines such as painkillers, nose drops or sprays, cough syrups and drops, throat lozenges and decongestants.
• If you have Covid-like symptoms, please stay at home and get tested.
Source: Ministry of Health