To the Editor: Australia and the other member nations of the World Health Organization’s Western Pacific Region were declared free of circulating endemic poliovirus in 2000, although the last case of endemic polio in Australia occurred in the 1970s.1 Nevertheless, the low risk of vaccine-associated paralytic poliomyelitis (VAPP) persisted through the continued use of the Sabin live attenuated oral polio vaccine (OPV) until it was replaced by the Salk inactivated polio vaccine in the National Immunisation Program from 1 November 2005.2

Despite the eradication of indigenous wild poliovirus and the removal of the risk of VAPP, Australia cannot afford to be complacent with surveillance for cases of poliomyelitis. Polio is a highly infectious disease and is quickly spread through international travel. All countries risk importation of wild poliovirus from the four remaining endemic countries (Afghanistan, India, Nigeria and Pakistan) — as occurred in Indonesia and 11 other countries during 2005.3 Until the latest outbreak, involving over 300 cases, Indonesia had not reported a single case of poliomyelitis since 1995. Genetic sequencing of the wild polioviruses from Indonesia determined that they originated in Nigeria and were related to strains isolated in Sudan, Saudi Arabia and Yemen.

Australia is also at risk from imported vaccine-related strains of poliovirus, as indicated by two reports from the United States in 2005. The first was a case of imported VAPP in an unimmunised adult, who had been in close contact with an infant recently immunised with OPV, while in Costa Rica.4 The second report described isolation of OPV poliovirus type 1 with a significant number of mutations (referred to as vaccine-derived poliovirus [VDPV]) from unvaccinated members of a religious community.5 Given that OPV has not been used in the USA since 2000, the source of the virus is unknown. VDPVs have been associated with paralytic polio worldwide.

It is imperative that the Australian community maintains the current high rate of polio vaccination coverage, especially for travellers, which remains the best defence against all forms of imported polio. A surveillance scheme for investigation of children with acute flaccid paralysis, the major clinical presentation of poliomyelitis, was established in Australia in 1995. It is coordinated by the National Poliovirus Reference Laboratory and the Australian Paediatric Surveillance Unit (Box). While the scheme focuses on children, specimens from patients of all ages are tested. Notification of all cases with a clinical suspicion of poliomyelitis is essential for the detection of imported polio.