The head of the organisation's global influenza programme, Dr Sylvie Briand, said that the containment strategy during the last pandemic was 'not feasible' and that guidelines might have to be overhauled.
Any change to the guidelines would be likely to affect the UK's plans for future pandemics, which are based largely on the WHO's advice.
Speaking at a Health Protection Agency (HPA) conference on the international response to the H1N1 pandemic, Dr Briand questioned whether it was possible to contain a virus at source. 'Rapid containment was not feasible this time,' she said.
The WHO's pandemic preparedness guidelines were based on the emergence of a pandemic virus in isolated rural areas where containment would be practical. Instead, the H1N1 pandemic began in densely populated cities.
Dr Briand said the WHO needed to look at the conditions under which containment could be achieved. 'If it is not feasible then we must slow transmission.'
Experts are examining the international response to the pandemic and a draft consultation is due in the autumn. It will take a further two years before new preparedness plans are released.
HPA chief executive Justin McCracken defended the scale of the UK's response to what turned out to be a mild virus. The authorities had to assume the virus was a real and credible threat to public health, he said.