Skip to main content
    • Aa
    • Aa

Pandemic (H1N1) 2009 influenza in the UK: clinical and epidemiological findings from the first few hundred (FF100) cases


The UK was one of few European countries to document a substantial wave of pandemic (H1N1) 2009 influenza in summer 2009. The First Few Hundred (FF100) project ran from April–June 2009 gathering information on early laboratory-confirmed cases across the UK. In total, 392 confirmed cases were followed up. Children were predominantly affected (median age 15 years, IQR 10–27). Symptoms were mild and similar to seasonal influenza, with the exception of diarrhoea, which was reported by 27%. Eleven per cent of all cases had an underlying medical condition, similar to the general population. The majority (92%) were treated with antiviral drugs with 12% reporting adverse effects, mainly nausea and other gastrointestinal complaints. Duration of illness was significantly shorter when antivirals were given within 48 h of onset (median 5 vs. 9 days, P=0·01). No patients died, although 14 were hospitalized, of whom three required mechanical ventilation. The FF100 identified key clinical and epidemiological characteristics of infection with this novel virus in near real-time.

Corresponding author
*Author for correspondence: Dr R. Pebody, Health Protection Agency, Centre for Infections, 61 Colindale Avenue, London, NW9 5EQ. (Email:
Linked references
Hide All

This list contains references from the content that can be linked to their source. For a full set of references and notes please see the PDF or HTML where available.

3.RJ Garten , Antigenic and genetic characteristics of swine-origin 2009 A(H1N1) influenza viruses circulating in humans. Science 2009; 325: 197201.

5.Health Protection Agency. Epidemiology of new influenza A(H1N1) in the United Kingdom, April–May 2009. Eurosurveillance 2009; 14: pii=19213.

6.Health Protection Agency. Pandemic (H1N1) 2009 in England: an overview of initial epidemiological findings and implications for the second wave, 24 November 2009 ( Accessed 4 December 2009.

8.J McMenamin , Minimum dataset for confirmed human cases of influenza H5N1. Lancet 2008; 372: 2022.

9.Health Protection Agency. The First Few Hundred (FF100) Project. Epidemiological Protocols for Comprehensive Assessment of Early Swine Influenza Cases in the United Kingdom, 2009 ( Accessed 4 December 2009.

10.P Gates , Collection of routine national seasonal influenza vaccine coverage data from GP practices in England using a web-based collection system. Vaccine 2009; 27: 66696677.

12.J Ellis , M Curran . Simultaneous molecular detection and confirmation of influenza AH5, with internal control. In: JR Stephenson , A Warnes , eds. Diagnostic Virology Protocols. Humana Press (in press).

14.L Calatayud , Pandemic (H1N1) 2009 virus outbreak in a school in London, April–May 2009: an observational study. Epidemiology and Infection 2009; 138: 183191.

17.F Begum , RG Pebody .Influenza vaccine uptake among the 65 years and over and under 65 years at risk in England, winter season 2008–09. 2009 ( Accessed 4 December 2009.

21.E Miller , Incidence of 2009 pandemic influenza A H1N1 infection in England: a cross-sectional serological study. Lancet 2010; 375: 11001108.

25.FY Aoki , G Boivin . Influenza virus shedding: excretion patterns and effects of antiviral treatment. Journal of Clinical Virology 2009; 44: 255261.

26.LJ Donaldson , Mortality from pandemic A/H1N1 2009 influenza in England: public health surveillance study. British Medical Journal 2009; 339: b5213.

Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Epidemiology & Infection
  • ISSN: 0950-2688
  • EISSN: 1469-4409
  • URL: /core/journals/epidemiology-and-infection
Please enter your name
Please enter a valid email address
Who would you like to send this to? *