Everything Parents Need to Know About the Polio Vaccine

Thanks to the vaccine, polio is a relic of the past in the U.S.

A baby receives the polio vaccine.
Karl Tapales / Getty

Polio is a dinosaur of a disease, with suspected cases dating back to prehistoric Egypt. For a portion of the 20th century, the paralysis it sometimes caused represented one of the greatest public health threats to American life. Today, you’d be hard-pressed to find anyone who’s had polio — the last time a case originated in the United States was 1979.

For this, you can thank one of America’s longest-running vaccine campaigns. In the 70 years we’ve been vaccinating against polio (also known as poliomyelitis), cases worldwide have been reduced by more than 99.9%. There’s a real possibility that polio could be eradicated entirely within our lifetime. Of the three viruses that cause polio (known simply as Types 1-3), only Type 1 remains. Types 2 and 3 were declared eradicated in September 2015 and October 2019, respectively.

When the polio vaccine was first made available in the U.S. in 1955, the country had never undertaken a nationwide vaccine campaign before. That we even have a standardized vaccine schedule for children today is the direct result of both that campaign and the smaller (or, smallpox-er) ones that came before it.

The generation being born today may very well be the last that will need to be vaccinated against polio.

Polio Vaccine History

In the early 20th century, summers were terrifying for American parents. Warm weather and dense city living gave rise to near-annual epidemics of polio, with most cases appearing in children. It’s unknown what exactly caused this sudden surge of an ancient disease, though some medical historians have suggested that advances in the availability of clean drinking water kept people away from contaminated water sources that would otherwise have inoculated them against polio as infants.

The majority of polio infections were asymptomatic, but a small portion of infected people experienced fevers, fatigue, and other flu-like symptoms. In an even smaller portion of cases, these symptoms gave way to paralysis and/or deformities, a result of the virus’s focused attacks on the nervous system. Though the percentage of paralytic cases was small, the overall number of infections grew so large that by the 1940s, more than 35,000 people were left disabled by the disease each year. And even those who suffered mild cases could be hit by the sudden onset of pain, weakness, and fatigue in the form of post-polio syndrome years later.

At the time of the polio surge, American vaccine science was increasingly becoming torn between two camps. The smallpox vaccine, which had been so successful not 200 years earlier at eradicating that virus, had been a live-virus vaccine, one with a weakened form of the living virus that could stimulate the production of protective antibodies. But more recent vaccines, including those for tetanus and diphtheria, had used killed versions of viruses that could still promote antibody development, an option seen as less risky but potentially less effective over time.

Ultimately, the first promising polio vaccine, which came from Dr. Jonas Salk at the University of Pittsburgh, used a killed version of the virus. Salk’s clinical trials, which eventually included dosing his own family, began in 1952, and his inactivated polio vaccine (IPV), was made available to the public in 1955.

The development of Salk’s vaccine was funded by the National Infantile Paralysis Foundation, now known as the March of Dimes. The foundation was established by President Franklin D. Roosevelt, who was famously paralyzed by polio at age 39.

The Oral Polio Vaccine and Sugar Cube

In 1961, a researcher named Albert Sabin finished development of a live-virus polio vaccine, providing a viable alternative to Salk’s IPV. Sabin’s oral polio vaccine (OPV), often fed to children as a droplet on top of a sugar cube, was easier to administer, cheaper to make, and capable of indirectly inoculating people who came in close contact with a vaccinated individual via transmission of the live virus particles. On the other hand, unlike the IPV’s inert virus, the OPV’s live virus was capable of accidentally causing polio instead of inoculating against it. Although such rare cases did occur, the risk was deemed small enough that the benefits outweighed them, and in 1963, OPV replaced IPV as the standard vaccine administered in the U.S.

By 1996, polio had been absent for decades in the U.S., and a recommendation was made by the Centers for Disease Control and Prevention (CDC) to switch back to IPV, as the risk of developing polio from OPV was considered greater than the threat posed by polio itself. A combination vaccine schedule was adopted for a few years, and in 2000, OPV was phased out entirely. Children in the U.S. now only receive the IPV vaccine.

All 50 states have required the polio vaccine for school attendance since at least 1980. Eradication in the U.S., completed in 1979, however, was achieved without any form of vaccine mandate.

When Do Babies Get the Polio Vaccine?

The polio vaccine schedule involves four injections before the age of six. Children should receive their first dose at two months, their second dose at four months, their third dose anytime between six and 18 months, and their final dose between the ages of four and six. In cases where a young child will be traveling to a country where they will be at higher risk of exposure to polio, the CDC recommends an accelerated vaccine schedule.

As always, it never hurts to contact your pediatrician before any international travel with a child.

Polio Vaccine Effectiveness

After two doses of the polio vaccine, a child is highly protected against the disease; the two doses of the vaccine are 90% effective. At the three doses, the vaccine is 99% or even 100% effective, according to the CDC.

Polio Vaccine Ingredients

Your child may be given IPV as part of a combination vaccine, an injectable that provides multiple vaccinations within one shot. IPV is commonly combined with DTaP (the vaccine that inoculates against diphtheria, tetanus, and pertussis), and can also contain a vaccine for hepatitis B or an infection known as Hib, depending on the brand. Combination vaccines are preferred when possible for children today, and are completely safe and effective.

The IPV active ingredients within any combination vaccine are the same, and consist of antigens, or immune-triggering substances, from each of the three types of poliovirus. It’s the presence of antigens, rather than viral particles themselves, that mark a killed vaccine. The vaccine will also include small amounts of several trace preservative ingredients that allow the antigens to arrive ready to do their best work. One of these ingredients may be formaldehyde, but that shouldn’t be cause for alarm — the amount of formaldehyde that may be in a vaccine is so small, and so diluted, that it’s about 1,500 times less than the amount that an infant’s body naturally produces.

Polio Vaccine Side Effects

We’ve said it before and we’ll say it again: When it comes to vaccines, side effects mean it’s working. Common side effects of IPV include aches, fatigue, tenderness at the site of the injection, and low-grade fevers (up to about 102°F).

If you have an infant experiencing discomfort after their first or second round of vaccination, try a cool sponge bath, or ask your doctor about non-aspirin pain relief. For older kids, remind them it’s not every day you get to be a living record of scientific history.