Pediatricians take heart.

Yes, I know it is discouraging when families occasionally ignore our advice and refuse vaccines for their children. It is even worse when political leaders who ought to know better question the safety and value of vaccines.

But let’s not lose perspective. Let me share a quick reminder of why vaccines are (almost) universally considered one of the greatest public health achievements of the 20th century.

Not long ago, I reviewed a clinical case with students as part of a medical microbiology course. A 6-year-old girl presented with fever, headache, and flaccid paralysis of the right arm with areflexia. With little prompting, the students generated a short differential diagnosis. Enterovirus. West Nile virus. “I guess we should include polio,” one student offered. “But who gets that anymore?”

A mere 120 years changes everything. At the dawn of the 20th century, we didn’t even know with certainty what caused polio, although infection was suspected.

The 1898 edition of An American Text-Book of the Diseases of Children included a chapter on acute anterior poliomyelitis. “The acute onset, the duration of fever, its comparatively uniform range, and the immediate paralysis point to a systemic infection,” the authors wrote.

On Sept. 9, 1954, the Courier-Journal, a newspaper in my hometown of Louisville, Ky., carried a story about the annual number of polio cases in Jefferson County, noting that they had reached 198 and General Hospital had opened a polio ward usually reserved for epidemics. Concerns about the infection were rippling throughout the state, and the paper reported that at least one high school marching band had elected to withdraw from annual Kentucky State Fair competition because of concerns about infection.

My mom was 10 years old in the summer of 1954, and she recalls that it was a “scary” time. Swimming pools closed. Parents refused to allow their children to go to movie theaters or the local amusement park because of fear that they might come into contact with the virus. My mom said, “Then one of my friends was diagnosed with polio. We had played together the week before she got sick. We worried that we were going to get sick, too. And once you got sick, you didn’t necessarily get better.”

Courtesy Wikimedia Commons/Shobhit Gosain/Creative Commons License

The same edition of the newspaper carried an Associated Press story posted from Rome about the third International Poliomyelitis Conference. American scientists Jonas E. Salk, MD, Albert B. Sabin, MD, and John F. Enders, PhD, hailed as leaders in the war on polio, were applauded when they announced that “prospects are good for a vaccine which may eventually give long-term protection against the disease.”

I probably don’t need to remind you that both Dr. Sabin and Dr. Salk did develop successful poliovirus vaccines. Dr. Enders, along with junior colleagues Fred C. Robbins, MD, and Thomas H. Weller, MD, developed the techniques to grow poliovirus and other viruses in culture, making the work of Dr. Sabin and Dr. Salk possible. For this, Dr. Enders, Dr. Robbins, and Dr. Weller received the Nobel Prize in 1954.

Regarding the prediction of long-term protection, I’d say we’re there. According to the Centers for Disease Control and Prevention, wild poliovirus cases have declined more than 99.9% since 1988. According to the Global Polio Eradication Initiative, that means that there are approximately 10 million people walking today who would have otherwise been paralyzed by the disease.

In 2015, there were only 74 cases identified in the world, and these were localized to two countries. Even better, a global commission announced that wild poliovirus type 2 had been eradicated from the world. Eradicated. The last known transmission occurred in India in 1999.

Type 3 poliovirus may not be far behind. The last known case of wildtype poliovirus 3 was detected in 2012.

The complete story of poliovirus eradication efforts could read like a suspense novel: There have been twists and turns, some missed deadlines, and now a bit of irony. Success, in large part, has hinged on the use of trivalent, live attenuated oral poliovirus vaccine (tOPV) throughout much of the world. Now eradication of all polio disease is going to require withdrawal of OPV in countries that still use it.

Rarely, the live attenuated vaccine viruses contained in OPV can cause polio, and since 2012, vaccine-derived cases have exceeded wild poliovirus cases. Vaccine-derived cases include vaccine-associated paralytic polio (VAPP) – paralysis occurs in a vaccine recipient or a close contact – as well as cases of circulating vaccine-derived polioviruses (cVDPVs). Remember that vaccine viruses are shed in the stool, and in communities with low immunization rates, they circulate and acquire mutations that confer the transmissibility and neurovirulence properties of wild viruses. Ultimately, cVDPVs lead to outbreaks.

In 2013, the Global Polio Eradication Initiative published a new “endgame plan” for polio that outlined a stepwise approach for removing OPV from immunization programs. First, it called on all countries to introduce at least one dose of inactivated poliovirus vaccine by the third quarter of 2015, immunizing infants at 14 weeks or at first contact thereafter. Second, it called for all countries to replace tOPV with a bivalent vaccine containing only types 1 and 3 by 2016. Given the eradication of wild poliovirus type 2, keeping type 2 in the oral vaccine just creates risk. An estimated 40% of VAPP cases and 98% of cVDPVs detected since 2012 were caused by poliovirus type 2. The type 2 component of tOPV also interferes with the immune response to the other types. Once poliovirus eradication has been achieved and certified, hopefully no later than 2019, all OPV will be withdrawn.

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So far, efforts remain on track. In 2016, all countries using countries OPV – 155 of them – simultaneously made the switch from oral polio vaccine to a bivalent vaccine.

What’s the role of pediatricians in the United States in polio eradication? For now, our job is to continue to protect all children in the United States against all three types of poliovirus. Current Advisory Committee on Immunization Practices (ACIP) recommendations specify 4 doses of trivalent inactivated poliovirus vaccine (IPV) at ages 2 months, 4 months, 6-18 months, and 4-6 years. Children vaccinated outside the United States with bivalent vaccine, including immigrants and refugees, will need to be revaccinated. Those without appropriate documentation of vaccine (written, dated records that specify trivalent vaccine) also should be revaccinated.

Serologic testing for immunity is no longer recommended. In the past, children without documentation of vaccines could be tested for neutralizing antibodies to poliovirus types 1, 2, and 3. Moving forward, serologic testing for antibodies to poliovirus type 2 won’t be available because it requires live virus, and in accordance with World Health Organization recommendations, laboratories have been destroying supplies of poliovirus type 2.

We also need to make sure that our patients who are traveling internationally receive all recommended vaccines, including a dose of IPV when appropriate. Specific recommendations can be found on the CDC’s pages for travelers.

A 2015 statement from the American Academy of Pediatrics called on pediatricians to consider polio as a potential diagnosis of any child presenting with fever and acute flaccid paralysis (Pediatrics. 2015 Jan;135[1]:196-202). When polio is suspected, public health authorities should be notified and two stool samples collected 24 hours apart, and within 14 days of the onset of paralysis, sent for testing. According to lead author Walter A. Orenstein, MD, “because most polio infections are silent, a case of paralytic polio in the United States may have been acquired from an asymptomatic individual, so a history of travel to a polio-infected area may be absent in the case of paralysis.”

I’ll second what my mom said. Scary.

Dr. Bryant is a pediatrician specializing in infectious diseases at the University of Louisville (Ky.) and Kosair Children’s Hospital, also in Louisville. She said she had no relevant financial disclosures. Email her at pdnews@frontlinemedcom.com.

It isn’t over until it’s over