A generally mild disease that sometimes killed

One year on from the start of the 21st century's first influenza pandemic, it is a good time to take stock of how the outbreak evolved and what has been learned. Although we now know that many infections were mild or inapparent, it is important not to forget the severe disease that it sometimes caused, and may still cause, in future winters.

During April 2009, reports from Mexico provided a worrying picture of unusually severe influenza in large numbers of healthy people including healthcare workers.1 The impact on hospitals was particularly marked with up to one in four specialist beds being occupied by patients with influenza, often needing highly specialised care and mechanical ventilation. Medical resources were exceeded by demand, and elective admissions and surgery halted; transmission to staff and to other patients was common, placing specialised nursing care, consumables, ventilators, drugs and containment facilities under great pressure.

Once cases began to appear in UK schools in May 2009, an intensive cooperative campaign of quarantine and antiviral prophylaxis was mounted by the Heath Protection Agency, the Department of Health and the NHS. Antiviral drugs have not been used in this way in previous pandemics; although it was unlikely that the spread of influenza could be halted, it was important to gather information about the pattern and severity of disease and to slow the spread, buying time for vaccine development and capacity building. Despite the public health campaign, the numbers of cases increased in London and the West Midlands, putting considerable strain on primary care. By 2 July, case numbers were rising sharply in most parts of the UK and containment measures no longer seemed appropriate. Routine antiviral prophylaxis was discontinued and a telephone helpline was launched on 23 July.2 Call centres took a history according to defined algorithms …