A second wave of the H1N1 influenza virus could result in larger numbers of severely ill patients that will require intensive care and are likely to be the most urgent burden on health services, the World Health Organisation (WHO) said.

The impact could overwhelm intensive care units and possibly disrupt the provision of care for other diseases in the northern hemisphere, the WHO said.

Some cities in the southern hemisphere have reported that nearly 15% of hospitalised cases have required intensive care.