Polio

Polio is a highly infectious viral disease predominantly spread through oral contact with faeces (water or objects). The virus is found in the mouth and intestines. Polio is a disease of poverty and largely affects children under 5 years. Three main serotypes were initially recognized but only wild serotype 1 exists today. Serotype 3 was declared globally eradicated in the 2019 and Serotype 2 in 2015. (WHO)

The global polio eradication program has been very successful, reducing the number of annual wild polio virus cases from over 300,000 cases annually in the late 1980’s to less than 10 now.

This remarkable success has been achieved through improvements in public health and hygiene and 2 types of vaccines. One, an inactivated injectable and the other a live oral vaccine.

The Salk (inactivated) vaccine was introduced into Australia during the 1950’s when the community was experiencing major outbreaks of paralytic polio. People born during this time will all remember school friends or relatives wearing calipers. Twenty to forty thousand people were diagnosed with paralytic polio between the 1930’s and 1960’s. The number of deaths peaked at 357 in 1951. The first Salk vaccines were introduced into Australia in 1956. Cases reduced but the coverage was not good enough to prevent a further outbreak in 1961 and 62. Sabin’s oral vaccine was first used in Australia in 1966. Many children of the 50’s received follow up Sabin vaccine.

The OPV (oral polio vaccine) had advantages over IPV (inactivated polio vaccine). It can provide inexpensive mass protection against the transmission of polio. However, there is a risk of the live strains reverting to a more virulent form of polio. When the risk of vaccine associated polio became higher than polio from the wild strain, most high-income countries changed back to the inactivated form and combined it with other childhood vaccines. Australia changed to the IPV in 2005.

Australia was declared polio free in 2000. In 2020 the IPV coverage was over 95%.

The last case reported in Australia was in 2007, where the individual contracted the infection in Pakistan.

The risk of exposure to polio for most travellers is very low. This presumes that most travellers are fully vaccinated. We know that 95% children who are born in Australia receive their childhood vaccinations. An unvaccinated individual might be protected in Australia but not when travelling.

The risk of international exposure to the wild virus is very low with only 3 countries reporting cases in the last 12 months (Afghanistan, Pakistan, Mozambique). The main concern for travellers is the potential exposure to vaccine associated paralytic polio (VAPP). Large outbreaks of VAPP have been reported in Central and West Africa and the Middle East. 

Most of these countries have poor public health infrastructures where safe water cannot be assured.

A one-time adult polio booster might be offered to those intending to visit these countries. This group includes long-term expatriate workers, international volunteers working in NGO’s and those intending basic travel with high-level community exposure.

It is interesting to note that both the UK and the USA have reported vaccine associated strains in their respective sewage. Both countries have excellent public health infrastructure and the risk to the public would be minimal.

The polio vaccine (IPOL) is a safe and effective vaccine. If you undertake frequent travel to low-income countries, then you might choose to have a one-time adult booster.