This year's flu vaccine did not not offer protection against a virulent strain which has infected thousands.

Three young people have died from complications after contracting the Hong Kong strain of influenza B.

Ministry of Health Chief Advisor Pat Tuohy says the World Health Organisation did not issue a warning about this particular strain, so it was not included in this year's vaccination. He says the current outbreak is significant, with thousands of children affected.

The outbreak comes as a new campaign is launched, to reduce the spread of viruses amongst children.

Virologist Dr Lance Jennings says children are particularly susceptible to viruses and on average, have one respiratory infection every two months. He says germs spread through schools like wildfire.

Dr Jennings suggests the use of anti-viral tissues which kill bugs as soon as they hit the tissue.