Hongkongers will experience an unusually cold Christmas Eve morning, and a disease expert is urging parents to take their children to get flu shots. The Observatory said an 'intense' cold winter monsoon would affect southern China in the next couple of days. It expects the temperature to drop overnight to a minimum of 11 degrees Celsius today (2-3 degrees lower in the New Territories). Temperatures will range between 13 and 18 degrees on Christmas Eve, compared with 16.3 to 20.2 degrees on the same day last year. But Christmas Day is expected to be a comfortable 15 to 20 degrees this year, similar to the 16 to 19.4 degrees last year. As the mercury drops to the low teens in the next two days, flu experts say the young will be the most vulnerable to weather-related cold. Thomas Tsang Ho-fai, controller of the Centre for Health Protection, expects the peak flu season to hit in about one or two months' time. He urged parents to get their children vaccinated now for seasonal flu. Children need two shots four weeks apart for proper immune response, he said. The Department of Health launched a pilot scheme last month to subsidise flu vaccinations for children, giving HK$80 for every flu shot by 1,200 private doctors. So far, 48,000 flu shots have been given to children aged six months to six years old, Dr Tsang said. This meant a take-up rate of just 8 per cent of the 300,000 children in the age group. The coverage rate in most developed countries is between 20 to 30 per cent. 'I am making an appeal to parents to take their children to doctors who are participating in this scheme to get the flu shot,' Dr Tsang said. 'This is the last chance in the sense that most children will require two shots' four weeks apart, before the flu season hits, he said. Dr Tsang said the authorities would decide whether to extend the vaccination programme beyond March 31, if it proved effective in reducing severe hospital admissions from seasonal flu.