More than half of the victims of a swine flu pandemic three years ago were school children and school closures proved to be a practical way to slow the spread of the disease, a study has found.
Between May and September 2009, 25,473 cases of influenza A (H5N1) were reported, forcing the closure of all kindergartens, primary schools and special schools, as well as secondary schools with many cases.
The study by Chinese University researchers found that the illness hit pupils at the start of the pandemic and spread to working adults and then younger children.
Elderly people were the least likely to be infected, and researchers speculated that they may have developed immunity in their younger days.
Reviewing the pattern of the outbreak, the researchers found that 54 per cent of those infected were pupils, and pointed out that cases involving children predominated during the first two weeks of the pandemic, in May.
'School-age children are usually the main transmitters of human influenza as a result of their high contact intensity with peers,' the study, published in the Hong Kong Medical Journal yesterday, said.
The researchers said that acting faster and closing all schools in a district, rather than individual schools where cases had been recorded, could theoretically be a more practical way of slowing transmission.
More adults began to contract the disease after the first two weeks, accounting for 33.4 per cent of all cases. The report suggested the disease was transmitted more slowly between adults because of different networking patterns.
Infants made up 11.1 per cent of the flu victims, while people aged 65 and above made up 0.9 per cent.
The World Health Organisation put the number of deaths from the global pandemic at 18,500.
The first known case in Mexico was identified in March 2009 and the disease rapidly spread around the world, causing panic. The disease arrived in Hong Kong in May, when a Mexican tourist was found to have the disease and Wan Chai's Metropark Hotel was quarantined for a week.
In a separate study, also published by the Journal, researchers found that 1.8 per cent of women who took the morning-after pill in the city became pregnant, higher than the figure of 1.1 per cent reported internationally by the WHO.
The Family Planning Association, which issues the pill in the city and which conducted the study, said there was no evidence to suggest that the figures were a result of delays in taking the pill or multiple episodes of unprotected sex.
The paper found that the pill was requested 11,014 times between 2006 and 2008, and said that a significant number of people sought the pill after problems with a condom, such as slippage or splitting. It urged the government to continue to educate the public about contraception.
The number of people who died in Hong Kong after contracting the disease three years ago