Table 1. Circulation of influenza A strains reflected by proportion of influenza isolates submitted to the virology laboratory of the Department of Health in Hong Kong (2003–2011).
| Year | Number of Isolates | H1N1 | H3N2 | ||
| Strains | No. of isolates (%) | Strains | No. of isolates (%) | ||
| 2003 | 1428 | A/New Caledonia/20/99(H1N1)-like | 9 (0.6%) | A/Moscow/10/99(H3N2)-like | 1419 (99.4%) |
| 2004 | 4542 | A/New Caledonia/20/99(H1N1)-like | 26 (0.57%) | A/Fujian/411/2002(H3N2)-like | 4561 (99.4%) |
| 2005 | 4692 | A/New Caledonia/20/99(H1N1)-like | 410 (8.7%) | A/California/7/2004(H3N2)-like | 4282 (91.3%) |
| 2006 | 3090 | A/New Caledonia/20/99(H1N1)-like | 2880 (93.2%) | A/California/7/2004(H3N2)-like | 210 (6.8%) |
| 2007 | 4742 | A/New Caledonia/20/99(H1N1)-like | 127 (2.6%) | A/Wisconsin/67/2005(H3N2)-like | 4615 (97.4%) |
| 2008 | 3237 | A/Solomon Islands/3/2006(H1N1)-like | 1677 (51.8%) | A/Brisbane/10/2007(H3N2)-like | 1560 (48.2%) |
| A/Brisbane/59/2007(H1N1)-like | |||||
| 2009 | 36289 | A/Brisbane/59/2007(H1N1)-like | 2855 (8.0%) | A/Perth/16/2009(H3N2)-like | 7252 (20.2%) |
| A/California/7/2009(H1N1)-like | 25633 (71.7%) | ||||
| 2010 | 7138 | A/California/7/2009(H1N1)-like | 2874 (40.3%) | A/Perth/16/2009(H3N2)-like | 4264 (59.7%) |
| 2011 | 5085 | A/California/7/2009(H1N1)-like | 3782 (74.4%) | A/Victoria/361/2011(H3N2)-like | 1303 (25.6%) |
Strains with decreased homology from the previous year are denoted in bold.