Actually its not like a strait forward request from CO rather it seems Polio evidence is asked unintentionally. The original text are given below:
""Sensitive
Dear Sir/Madam
In order to be able to finalise this case would you please attend to the following.
Evidence of Polio vaccination
On 5 May 2014, the World Health Organization (WHO) Director General declared the recent international spread of wild type polio virus to be a ‘public health emergency of international concern’ under the International Health Regulations (IHR). Ten countries, listed below, have been identified as having suffered recent outbreaks of Polio. Applicants who have spent 28 days or longer in any of the 10 countries listed below on or after 5 May 2014 are required to provide their current certificate of vaccination.
As you are an applicant who has spent 28 days or longer in of these countries on or after 5 May 2014, you are requested to provide your current certificate of vaccination. Please note that failure to provide this certificate may result in unnecessary delays to the processing of your visa application.
Countries: Afghanistan, Cameroon, Equatorial Guinea, Ethiopia, Iraq, Israel, Nigeria, Pakistan, Somalia, Syria
Further information is available from www.immi.gov.au/allforms/health-requirements/threats-public-health.htm
Please submit the required certificate within 28 days of receiving this request. As this is an email request you will be deemed to have received the request today.
Regards"