Surveillance of influenza and other respiratory viruses in the UK: 2010-2011 report
Synopsis During the first influenza season after the 2009/10 H1N1 influenza pandemic, the UK experienced intense influenza activity. Indices of activity in the community (such as NHS Direct and institutional outbreak surveillance) together with severe (hospitalised and fatal) influenza cases were reported in week 48. This occurred approximately two weeks before levels of consultations for influenza-like-illness (ILI) in sentinel GP schemes began to rise above traditional “baseline” levels. Also in week 48 an increase in the proportion of cold/flu calls to NHS Direct was also reported, after the early warning threshold was breached on 2 December 2010. Overall, influenza activity in the UK in 2010/11 reached a level higher than that seen in the winter of the 2008/09 season and 2009/10 winter season of the pandemic, but lower than during the first wave of the pandemic in the summer of 2009. Clinical indices peaked between late December 2010 and early January 2011 in England, Wales, Scotland and Northern Ireland. Both influenza A/H1N1 (2009) and influenza B circulated at the same time. A prolonged tail to the season was noted (particularly in Scotland), as indicated by continued swab positivity for influenza B. Influenza was reported more often in young and middle-aged adults in the 2010/11 season than seen in the previous pandemic period in 2009/10. Outbreaks, mainly caused by influenza A/H1N1 (2009) and influenza B, were reported in schools, care homes, hospitals, prisons, a nursery and a military base. The occurrence of severe hospitalised cases resulted in increased intensive care unit bed occupancy, primarily in under 65 year olds. Severity indicators suggested a higher level of morbidity in terms of the daily number of cases of confirmed or suspected influenza in critical care compared to the 2009/10 pandemic. Mortality, in terms of excess deaths and individual fatal cases, was also higher in 2010/11 than the 2009/10 pandemic. Total excess deaths, however, were lower than seen in the 2008/09 season. Influenza A/H1N1 (2009) was the predominant strain detected, with virological activity reflecting clinical activity. In addition, a significant proportion of virus detections due to influenza B were reported. In Europe, the predominant circulating strains varied between countries. Of the influenza A/H1N1 (2009) viruses tested in the UK, 3.1% were found to carry the mutation commonly associated with resistance to oseltamivir. While reports of concurrent bacterial infections (CBI) were not identified as a major feature of the 2009 pandemic, there were reports of CBI associated with influenza infection during the 2010/11 season, prompting an alert for clinicians issued by the Chief Medical Officer. In England, the proportion of over 65 year olds who received the 2010/11 seasonal influenza vaccine reached 72.8% by the end of the season, a slight increase on the previous year. For people aged under 65 years in a clinical risk group, a slight decrease to 50.4% uptake was seen. Pregnant women were incorporated into the seasonal influenza vaccine programme in the UK for the first time in 2010/11, following the pandemic. Vaccine uptake in England was 36.6% among healthy pregnant women and 56.6% in pregnant women with an underlying clinical risk factor. Data from the final monthly collection of flu vaccine uptake by frontline healthcare workers show 34.7% were vaccinated by 28 February 2011.