Polio making a comeback?

In July, a 20-year-old man in Dockland County, N.Y., was diagnosed with polio, a highly contagious, disabling, and potentially fatal disease caused by the polio virus (hereafter referred to as polio).

On June 22, the U.K. Health and Safety Executive announced that the poliovirus has been detected repeatedly in sewage in London, England, but no cases have been reported. During the same period, Israel reported that the virus was also found in sewage in Jerusalem.

In recent articles in the world's top scientific journals Nature and The Lancet, these events herald an unexpected and worrisome development in humanity's long-running battle against polio: the re-emergence of poliovirus in developed countries with good sanitation; the possibility that the actual spread and magnitude of the virus may be more widespread than is currently known; and thus the potential for more cases in vaccinated individuals cases of paralysis.

According to the WHO, polio primarily affects children under five years of age. One case of irreversible paralysis occurs in every 200 cases, and of the paralyzed cases, 5% to 10% die from respiratory muscle paralysis. Polio cannot be cured, but it can be prevented with a safe and effective vaccination.

Polio is also one of the few diseases that can be eradicated, with the number of cases caused by the wild poliovirus decreasing by more than 99 percent since 1988, from an estimated 350,000 cases at the time to six cases reported in 2021. However, as long as one child remains infected with poliovirus, children in all countries will remain at risk of contracting the disease. Failure to eradicate it in all countries could lead to a global resurgence of the disease. And low vaccination rates in recent years due to the new crown outbreak could undermine years of hard-won progress.

Outbreaks emerge in multiple countries

The discovery of traces of the polio virus in New York's wastewater comes on the heels of a series of ominous signs around the globe.

Malawi, Africa, announced its first case in 30 years in February, when a 3-year-old girl was paralyzed after contracting the polio virus. The case can be traced back to cases reported in Pakistan. Pakistan has reported 14 cases this year.

In March, Israel reported its first case of childhood polio paralysis since 1988. The virus was also detected in several other children, but there were no symptoms, and almost all cases were not vaccinated.

In June, British authorities declared the polio virus an "incident of national concern" after it was found in sewage, and in July, polio was detected in sewers in New York after cases of paralysis, suggesting that the actual spread of the virus may be even wider.

Notably, the infected man in the U.S. was not vaccinated and did not travel abroad during the time he may have been exposed to the virus, suggesting he was infected domestically after the U.S. had declared polio eradicated.

"No country in the world is immune to polio," Nature quoted Fulfill Bhutto, a global health researcher at the Ag Khan University in Karachi, Pakistan, as saying, "It's all interconnected. "

Are vaccines to blame?

Genetic analysis showed that the viruses in the three developed countries mentioned above are all vaccine-derived polio virus type 2 (AVDP), which means they are mutated versions of a virus derived from an oral vaccine.

There are three wild polioviruses. type 2 was declared eradicated by WHO in 2015 and type 3 in 2019. Only poliovirus type 1 is still not eradicated, and it is only transmitted in Pakistan and Afghanistan.

There are two main types of polio vaccines in widespread use: inactivated vaccine (IV), which is administered intramuscular, and oral vaccine (OP), both of which are certified by WHO as safe and effective.

The oral vaccine has been used in many countries since 1988 and has been instrumental in helping to eradicate polio in developing countries because of its affordability, ease of administration and use, and its ability to protect entire populations at risk of transmission.

However, the oral vaccine has long been controversial because it contains a weakened form of the live virus. In extremely rare cases, attenuated viruses can sometimes mutate into transmissible live viruses in compromised populations and cause outbreaks in vaccinated populations through the feces of vaccinated individuals, especially in areas with poor sanitation and low levels of vaccination.

An increasing number of countries that have eradicated polio are now turning to inactivated vaccines to avoid such risks. Last year, WHO also announced that it was developing a new, more stable, and safe oral vaccine.

It is not clear how far the polio virus has spread in the United States, the United Kingdom, and Israel. The U.S. Centers for Disease Control and Prevention says all cases have been linked to people who have not been vaccinated or have weakened immune systems. Most U.S. adults were vaccinated as children and can be adequately protected.

Call for vigilance

After smallpox, polio is the disease most likely to be eradicated from humans. The disease once terrorized countless families and paralyzed hundreds of thousands of children worldwide each year.

After the first vaccine was introduced in 1955, global polio cases fell by 99 percent - from 350,000 cases of paralysis in 1988 to six cases reported in 2021. For those who are vaccinated, the virus is virtually risk-free. But scientists point out that the New Crown pandemic has disrupted routine vaccination programs in many countries and made them more vulnerable to the resurgence of polio, making an urgent call for countries to increase vaccination rates, especially among children.

The Nature article notes that the discovery of poliovirus resurgence in countries such as the United Kingdom and the United States should be a wake-up call and that comprehensive testing should be made for factors contributing to the emergence of virus transmission in settings where only inactivated vaccines are used, national vaccine coverage is high and sanitation is good.

Polio and iconic pneumonia, as well as monkeypox, which was just declared this year, are the only three public health emergencies of international concern (CEPHEID) currently considered by the WHO. It is important to note that a public health emergency of international concern is not the same as a large-scale global outbreak. On the contrary, polio has been virtually eradicated from the world and is currently endemic in only a few countries. However, with the goal of polio eradication close at hand, any sustained outbreak in countries that remain vulnerable would be a catastrophic setback. Therefore, since 2014, WHO has maintained polio at this highest level of alert status and continues to update concerns.