IRELAND'S schools are on the brink of another deadly swine flu epidemic as the number of cases jumped threefold last week.
Maternity hospitals have been put on high alert for cases of the virus as seven pregnant women with swine flu required hospitalisation.
And the Health Protection Surveillance Centre (HPSC) is monitoring a network of schools' absenteeism lists.
The HPSC has revealed that patients presenting with H1N1 virus increased from 30 to 91 in the last week of December.
The highest rates remained among those under 14 years of age.
And the figures are set to soar as thousands of children return to school after the Christmas break.
Dr Kevin Kelleher, head of health protection with the HSE, said that the number of swine flu cases have swelled with the severe weather.
"It is affecting more younger people than in previous years," he said. "In 2008 and 2009 it affected the over 60s, but this time it is the under 60s.
"The H1N1 virus has the propensity to cause more serious illnesses in women who are pregnant, so we would urge them to obtain the vaccine."
Five patients were admitted to intensive care within the last week and 34 required hospitalisation as the numbers presenting to GPs soared by 150pc.
During the last flu season, a total of 24 people with H1N1 died in Ireland.
"During week 51 in 2010, influenza activity increased significantly across Ireland," the HPSC said.
It also said that 19 of the confirmed cases of flu were among pregnant women, and 18 of those had swine flu.
The HSE has offered pregnant women the seasonal flu vaccine since September. The executive said that most people who get the flu are able to self-medicate and be looked after at home.
"However, as had been anticipated, this winter some people have been hospitalised as a result of their illness," a representative for the HSE added.
"In particular, the groups most affected by the swine flu virus were widely vaccinated, including children, young people, those with chronic illness and pregnant women."
The HSE said the best protection was the flu vaccine, which now includes the swine flu strain.
The HPSC says that swine flu has made up almost 90pc of the 120 confirmed cases of influenza so far this season
The symptoms of a typical flu are a sudden fever, headache, muscle aches, a dry cough and sore throat.
The average duration of infection is 10 to 14 days.