(updated on 2011/04/04)
The second wave (updated) 第二波 (更新)
In 2009, swine flu was the dominant virus in influenza epide mics around the world, the causative virus if which is now commonly referred as Influenza A (H1N1)2009. In Hong Kong the epidemic peaked in September 2009, leaving people to guess when the second wave would arrive. Swine flu did not come back in the following two influenza seasons in 2010. Outbreaks however began to occur in late January 2011. The map shows the locations of school outbreaks of influenza-like illness (red circles) in the 10-week period from the last week of January 2011, against the distribution of student cases (age 5-19) reported during the 2009 epidemic in the background (grey to black in colour). Interestingly most of these were located in DCCA (District Council Constituency Areas) where a lower number of cases were reported in 2009. It is likely that H1N1 transmission in this second wave took place more readily in geographic areas less affected in the previous epidemic. A higher number of reported cases in the past then could well mean that more students have become immune before the second wave arrived. Data for the map were obtained from the daily update reports of Centre for Health Protection (www.chp.gov.hk) in Hong Kong.