Table 1.
Timing and intensity of influenza transmission in the cohort.
| Period | Year (months) seasona | Subtype | Strainb | % infected(95% CI)c |
|---|---|---|---|---|
| Pre-study | 2007 | H1N1 | Solomon Islands/3/06-like | – |
| 2007 | H3N2 | Brisbane/10/2007-like | – | |
| 2007 | B | Yamagata Florida/04/2006-like | – | |
| Bleed 1 | 2007 (12) Winter | |||
| Season 1 | 2008 (7–8) Summer | H1N1 | Brisbane/59/2007-like | 7.2 (5.3–9.7) |
| 2008 (8–9) Autumn | H3N2 | Brisbane/10/2007-like | 2.3 (1.3–4.0) | |
| 2008 (2,4,6,9,10,12) | B | Yamagata Florida/04/2006-liked,e | 12.6 (10.1–15.6) | |
| Bleed 2 | 2008 (12) Winter | |||
| Season 2 | 2009 (4) Spring | H1N1 | Brisbane/59/2007-like | 8.6 (6.6–11.0) |
| 2009 (4–6) Spring | H3N2 | Perth/16/2009-like | 13.1 (10.7–16.0) | |
| 2009 (4) Spring | B | Victoria Cambodia/30/2011-likee | 10.5 (8.3–13.1) | |
| Bleed 3 | 2009 (6) Summer | |||
| Season 3 | 2009 (9–12) Autumn | H1N1 | California/04/2009-like | 18.2 (15.3–21.5) |
| Bleed 4 | 2010 (4) Spring |
Months (January = 1 – December = 12) when influenza virus RNA was detected in swabs by RT-PCR.
Strain designation is based on National Influenza Surveillance programme data from Northern Vietnam coordinated by the National Influenza Center at the National Institute of Hygiene and Epidemiology. Strains considered to be antigenically distinct compared to those circulating previously are shown in bold.
The number of participants assessed is shown in Table 2.
This strain started to circulate just prior to study commencement and continued to circulate during the study.
Six influenza B strains were isolated in S1 and belonged to the Yamagata lineage whereas a single strain was isolated in S2 and belonged to the Victoria lineage (Table S1).