With one confirmed case of polio and dozens of positive wastewater samples dating back as far as April, New York has declared a state of emergency over the outbreak of the polio virus.

Officials stated that the declaration allows 'necessary State agencies to take appropriate action to assist local governments and individuals in containing, preparing for, responding to and recovering from this State disaster emergency.'

The first case was detected in Rockland County outside of New York City's Bronx on July 21 in an unvaccinated man in his 20s. Wastewater surveillance since has detected the virus within the city itself and in nearby Orange and Sullivan counties, with officials revealing on Friday that Nassau County, also just outside of the city had detected the virus in its wastewater surveillance - leaving the thought that the true number of infected New Yorkers could be in the thousands. 

Last month, the Center for Disease Control and Prevention (CDC) disclosed that further investigation found at least 21 positive samples of the virus in the state. 

Its side effects, according to the CDC, entail that around one-in-every-1,900 polio infections in unvaccinated persons will result in paralysis, but not much of a risk is posed for those vaccinated as more than 90% of Americans are vaccinated by their second birthday - and many had to receive the shot to attend public school. According to official data, 78% of New Yorkers have received at least three polio jabs by that age but no booster and vaccination in infancy, however, provide protection for a person's entire life.

Both Rockland and Orange county have vaccination rates in the 60s, significantly lower than the 95% mark set by the World Health Organization (WHO) to control the virus. "On polio, we simply cannot roll the dice," Dr Mary Basset, the state's health commissioner, said in a statement on the Nassau county findings, adding: "If you or your child are unvaccinated or not up to date with vaccinations, the risk of paralytic disease is real. I urge New Yorkers to not accept any risk at all."

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Although just one case is confirmed, officials worry that a massive outbreak is quietly going unnoticed. Dr. Patricia Schnabel Ruppert, the health commissioner for Rockland County, told the BBC that 'most cases are asymptomatic or mildly symptomatic, and those symptoms are often missed. So there are hundreds, perhaps even thousands of cases that have occurred in order for us to see a paralytic case.'

The Rockland County man initially experienced a fever, neck stiffness, stomach issues, and limb weakness. He was admitted to the hospital, and a stool sample later confirmed that he had a case of vaccine-derived polio.

This form of the virus comes as a result of the oral poliovirus vaccine (OPV), which delivers a person a live version of the virus and the body will usually kill the virus by generating antibodies - on some rare occasions the recipient will be infected.

The OPV is no longer used in the US, as it been replaced with the inactivated polio vaccine (IPV) which is delivered via injection but some developing nations still use the former because it is easier to access and activates antibodies faster than the latter.

Paralytic polio usually takes between seven to 21 days for an infected person to feel symptoms. Even though the man had no travel outside of the country, he attended a large gathering 8 days before symptom onset, which officials believe the exposure originated. Based on earlier polio outbreaks, New Yorkers should know that for every one case of paralytic polio observed, there may be hundreds of other people infected,' Basset warned in August.

In a report revealed by the CDC last month, 260 samples from Rockland and Orange counties were tested which came back with 13 samples from Rockland and 8 from Orange found to have traces of the virus.

The last time there was a polio outbreak in the US was back in the late 1940s, until the vaccine was developed in 1955.