Understanding the Polio Outbreak: History and Prevention

Historical Background

According to End Polio Now, the first documented polio outbreak in the United States happened in 1894 in Vermont. This outbreak led to 132 cases of permanent paralysis. By 1905, there was a general understanding that polio could be transmitted from person to person, and it was later determined to be a viral illness.

In 1916, a major polio outbreak in New York City killed over 2,000 people and resulted in 6,000 deaths nationwide. Beyond mortality, thousands of people were paralyzed by this epidemic.

The first significant breakthrough in disease prevention happened in 1954. Based on a timeline from the College of Physicians in Philadelphia, that is when the first polio vaccine trial began. One year later, the inactivated polio vaccine was announced as safe and effective and was then licensed for distribution in the US.

An oral version of the vaccine was then developed in 1959 by Soviet officials. Despite its cheaper and more accessible distribution, this vaccine had one major drawback: unlike the injectable virus, the oral virus could revert to its virulent form, causing paralysis.

In 1988, the WHO’s World Health Assembly launched the Global Polio Eradication Initiative (GPEI) alongside Rotary International, the CDC, and the United Nations International Children's Emergency Fund. This initiative, alongside other government programs, reduced the global polio prevalence by 99%.

By the late 1900s, polio had already been eradicated in many countries due to vehement vaccine efforts and campaigns. In 1988, there were approximately 350,000 polio cases; throughout 2021, there were only six reported cases.

Despite vaccination efforts, polio has reappeared in many countries such as the US and Ethiopia.

Poliovirus

Many people confuse the poliovirus with poliomyelitis. According to the CDC, poliomyelitis, commonly known as polio, is the illness caused by infection with the poliovirus.

The European CDC (ECDC) states that “polioviruses are small single-stranded RNA viruses that belong to the Enterovirus subgroup of the family Picornaviridae. Humans are the only reservoir for poliovirus.”

According to the CDC publication, the poliovirus has three different serotypes (or strains). The virus itself can be rendered inactive by heat and other environmental factors. Each serotype is distinct; immunity to one does not necessarily mean you are immune to all virus strains.

While all three versions of the virus can cause poliomyelitis, it is thought by the ECDC and other sources that type 1 is the predominant contributor to polio cases. Types 2 and 3 were eradicated in 1999 and 2012, respectively.

Furthermore, “the incubation period for nonparalytic poliomyelitis is 3–6 days. For the onset of paralysis in paralytic poliomyelitis, the incubation period is usually 7–21 days. The risk of severe disease and death following primary infection with poliovirus increases with increasing age,” states the publication.

Disease Transmission

Data from the CDC suggests that the poliovirus is very contagious, spreading through direct and indirect contact, and can stay inside the body for up to two weeks.

The virus typically enters the body through the mouth and multiplies in the throat and GI tract.

According to the New York State Department of Health, the virus “enters the body through the mouth, usually from hands contaminated with the stool of an infected person. Respiratory and oral-to-oral transmission through saliva may also occur.”

Symptoms

The CDC states that approximately 72% of people infected by the poliovirus may be asymptomatic and can still spread the virus.

Conversely, approximately 25% of patients who contract poliovirus will experience flu-like symptoms such as sore throat, fever, tiredness, nausea, headache, and stomach pain. On average, flu-like symptoms typically resolve within five days.

Less than 1% of people will experience more severe symptoms such as paresthesia, meningitis, and paralysis. Paralytic polio can be fatal as paralysis can lead to the cessation of breathing.

Prevalence

According to the ECDC and other sources, the poliovirus is most common in children under 5. Before vaccine development, it was a widespread pediatric virus.

The Global Polio Eradication Initiative (GPEI), started in 1988, has allowed for a 99% reduction in polio cases.

Prevention

Globally, there are two kinds of poliovirus vaccines available: (1) inactivated poliovirus vaccine (IPV) and (2) oral poliovirus vaccine (OPV). Over 99% of children who receive the polio vaccine will be protected from extreme versions of the disease.

According to the WHO, “OPV consists of a mixture of live-attenuated poliovirus strains of each of the three serotypes, selected by their ability to mimic the immune response following infection with wild polioviruses, but with a significantly reduced incidence of spreading to the central nervous system.”

In the US, physicians opt for the IPV vaccine to minimize the risk of virus reversal and infection in patients.

“To make IPV, poliovirus is purified and killed with a chemical (formaldehyde). IPV elicits antibodies in the bloodstream, not the intestines. It prevents the virus from traveling through the blood to the brain or spinal cord, thereby preventing paralysis. In a sense, because the vaccine induces antibodies in the bloodstream, and not the intestines, IPV induces a "second line" of defense against infection,” states the Children’s Hospital of Philadelphia (CHOP).

According to the CDC, the polio vaccine is a four-dose series given at 2 and 4 months, between 6 and 18 months, and between 4 and 6 years old.

Pediatric immunization against polio is a standard of care in the US, meaning that most American adults do not need polio vaccination in adulthood. However, the CDC recommends that adults in high-risk groups repeat the series. Risk factors include traveling to a country where the risk of infection is increased and working in a setting where exposure is likely such as a laboratory or healthcare facility.

Adults in these groups should consider a three-dose series with one to two months between the first and second dose and six months to a year between the second and third dose.

Looking Ahead

Because the disease persists despite the available resources and knowledge to prevent and eradicate the poliovirus, public health officials agree that the best way to avoid the further spread of the disease and work toward eradication is to continue vaccination efforts.

Parents are strongly encouraged to discuss vaccination and disease risk with their child's pediatrician. Additionally, adults who have not gotten the polio vaccine or are at high risk of infection should consult a licensed healthcare professional regarding immunization.