For the first time in nearly ten years, a case of polio was confirmed in the United States. Health officials in New York’s Rockland County discovered the case last month in a… unvaccinated 20-year-olddecades after polio was eradicated in the US 1979.
With the country and its public health system already struggling under the weight of Covid-19 and monkey pox, this news comes as an unpleasant surprise and immediately raises questions. How did this happen? Who else is at risk? What does it mean that the Rockland case is a… vaccine-derived strainand what are the implications for global efforts to eradicate polio completely?
What is polio?
Polio, short for poliomyelitis, is caused by the poliovirus, an enterovirus that can infect the nervous system. Symptoms can range from those similar to the flu (sore throat, fever and fatigue), to a more serious spinal cord infection that meningitis even paralysis. But unlike the flu, the polio virus multiplies mainly in the gut, and above all spreads when people don’t wash their hands after using the bathroom. Polio is very contagiousat least for the unvaccinated, especially in areas with poor hygiene and water safety.
Of the first documented US outbreak in 1894 until vaccines were developed in the 1950s, polio was one of the most common dreaded teething problems. Thousands of children were left behind paralysed with each summer break. The most vulnerable were: children under 5 years
But those victims were the exception; three quarters of poliovirus-infected patients show no symptoms at all. For most of the remaining quarter, the disease never progresses beyond flu-like symptoms. However, in about one in 25 patients, the virus spreads to the nervous system and causes meningitis. About one in eight of meningitis cases — or about 0.5 percent of total polio cases — will have permanent damage to their nerves that leave them paralyzed. There was and is no known cure, only supportive treatments, including the iron lung – since replaced by more advanced ventilators – and physiotherapy.
The threat of polio changed permanently when two vaccines were discovered in quick succession: an injected, inactivated vaccine by Dr. Jonas Salk in 1955 and a live attenuated vaccine taken orally by Dr. Albert Sabin in 1961. Both vaccines are very effective, conferring 99 percent immunity to infection. Sabin’s oral vaccine eventually became widely used in the US, and polio cases dropped dramatically in the 1960s and 1970s, until the wild virus was completely eradicated from the country.
The US led the way – a global vaccination campaign began in earnest in 1988, a few years after smallpox was eradicated in 1980. switched to the slightly safer inactivated injected vaccine in 2000, and the injections are still recommended to all children on the standard childhood vaccination schedule. Worldwide, thanks to ongoing public health effortsHundreds of millions of children receive the oral vaccine every year, and the original wild virus has been expelled from all but one handful of countries.
Where does this case come from?
Since the spread of polio in the community was eliminated from the US around 1980, all infections have come from other countries that still have the disease. Genetic Sequencing shows that the recent case was a vaccine-derived poliovirus strain. This means that the circulating virus is not from one of the few remaining areas of endemic wild polioviruses, but rather from one of the many other countries with polio outbreaks that have mutated from an oral, live attenuated vaccine – which is not the vaccine. currently used in the US.
Polio vaccines fit into one of two types: inactivated or live attenuated. Live Attenuated Vaccineslike the combined measles, mumps and rubella vaccine recommended to all U.S. children contains a modified, attenuated strain of a pathogen that does not cause disease in humans, yet elicits an immune response that protects against the original strain. The oral vaccine used in most high-risk countries is live attenuated. Inactivated vaccines, such as the polio vaccine currently used in the US, contain only dead virus material and may have a longer series of booster shots to stimulate the immune system enough to confer long-lasting and complete immunity.
Although the live attenuated polio virus vaccine almost never causes polio itself, except in the less than one in a million cases when a child is severely immunocompromised – the fact that it contains a live virus inevitably carries some risk, unlike inactivated vaccines. When Live Attenuated Polio Vaccines Are Given in a community containing a high percentage of unvaccinated people, the modified virus can infect others, and with enough generations of spread, it can – very rarely – mutate back into a new virulent strain. It is essential to public health efforts to ensure that enough people are vaccinated, to protect against both the wild virus and the possibility of new vaccine-derived strains.
Ironically, the fact that most cases of polio are asymptomatic or mild — along with an incubation period that can picking up up to 30 days before symptoms appear – making polio particularly challenging for contact tracing and public health containment efforts. The only way to suppress the virus is to achieve herd immunity, which is required for polio Vaccinate about 80 percent of the population.
Who is at risk?
For most people in the US, the newly discovered case of polio has not increased the risk at all. The Rockland County Public Health Department believes the patient… no longer contagious.
The polio virus can detected in stool samplesand also in wastewater monitoring, which searches for evidence of viral genetic material in sewage. On August 1, the New York State Department of Health reported that the case of polio in Rockland was genetically linked to samples of the virus collected in sewerage in Jerusalem and London, although the department emphasized that the results do not automatically imply that the patient had traveled to either location. Rockland’s public health department was able to use previously collected wastewater samples for Covid-19 monitoring, and polio virus found in samples there from June genetically linked to the current case.
Given how common asymptomatic cases are and the long incubation period, it is possible that there are other unrecognized cases in the Rockland area. Those can still be contagious, but chances are it won’t spread very far. From 2019, more than 90 percent of American children were fully vaccinated against polio on schedule, well above the herd immunity threshold, and this figure has kept stable for decades. Babies 4 months or older will usually have received two doses, which are already provides 90 percent immunity.
However, Rockland County has a lower vaccination rate than the rest of the country; it was the site of a 2018-2019 measles outbreakand currently alone 60 percent of 2-year-olds there are fully vaccinated against polio, compared to the national average of 90 percent. The New York Department of Health now urges all unvaccinated people, those who have not completed their polio vaccine series, and pregnant people to get vaccinated. In the month since the polio case was discovered, the Rockland clinic nearly 400 vaccine doses. People in the Rockland area who were vaccinated as children but are concerned they may have been exposed should schedule a booster shot.
What does this mean for global eradication efforts?
While the US remains protected from polio, the same cannot be said of some of the more risky developing countries where the virus is still active.
After his work developing the oral vaccine, Sabin campaigned for a worldwide eradication in the 1960s and 1972. donated all of its vaccine strains to the World Health Organization in the hope of reducing production costs. Despite recent efforts to use the slightly safer inactivated vaccine worldwidemost low- and middle-income countries still use the oralready vaccine.
The global extermination program has been huge good luck total, with total global polio cases are declining by more than 99.99 percent since the program’s inception in 1988. But the closer eradication becomes, the more difficult reaching the finish is. When hundreds of millions of doses of oral vaccine are given each year, even the very low risk of one dose producing a new vaccine-derived strain adds up. Most cases of polio discovered in African countries Like it Nigeria and Yemen to be vaccine-derived from. Breaks in vaccination coverage due to: military conflicts and the COVID-19 pandemic likely increased the risk of vaccine-derived variants spreading uncontrollably.
Despite the risks inherent in live attenuated vaccines, the oral vaccine has significant benefits, particularly for public health campaigns in developing countries. Each dose costs as little as 12 centscompared to about $2 per dose for the inactivated vaccine, and because it is given in drops under the tongue, no needles or trained professionals are needed to administer it. Live attenuated vaccines also generally provide stronger and longer lasting immunity than inactivated vaccines.
And in the beginning, the infectivity of the oral vaccine strain was actually considered a plus, as children who are not reached by health professionals can get the weakened strain from others, making them immune. In theory, as long as the vaccination campaign reached enough people in the community, the spread would disappear long before the virus had a chance to mutate back to virulence in humans.
Phasing out the oral vaccinepolio, which would eliminate the source of new polio variants, will likely be necessary to achieve complete eradication, but replacing the oral vaccine with the full schedule of booster injections needed to confer immunity is not yet possible. Even if funding and staff were available, the total global supply of inactivated vaccines would be: way too low to cover the hundreds of millions of children who are still at risk.
With monkeypox recently declared a public health emergency of international concern by the WHO, and the ever-present threat of future pandemics on the horizon, the global effort against polio is more important than ever to ensure that polio never happens again. so will be of global threat. To maintain and ideally increase vaccination coverage in the US will protect the country in the meantime and support the global drive to eradicate by keeping polio from taking hold.