Flu shots are clearly protective, even during though those years with poor matches between the vaccine and the circulating flu strains, say researchers at the University of Rochester Medical Center.

They looked at children between 6 months (the youngest able to receive the vaccine) and 5 years old in 2003-2004 and 2004-2005.

'These years were poor matches and fully vaccinated children were still half as likely to get the flu,' said researcher Dr Katherine Eisenberg.

She said that vaccinations could prevent thousands of hospitalisations each year.

In the 2004-2005 flu seasons, the vaccine was effective almost 60 percent of the time in children between 6 months and 5 years old who were fully vaccinated compared to those who were not. But oartial vaccination (receiving one shot when two are recommended) did not provide any protection. This highlights the importance of having children receive full vaccination. Receiving only partial vaccination has not been shown to protect children from flu, Eisenberg said.

'It is incredibly important for all children to receive flu vaccinations for themselves and for the people around them,' said researcher Dr Peter Szilagyi.

'Children are notorious for unintentionally spreading illnesses. If we can prevent them from getting sick in the first place, we can prevent their loved ones from getting sick, especially younger siblings under 6 months who can’t receive the vaccine and older grandparents who are at increased risk of complications from the flu.'