Polio, also known as poliomyelitis, is a virus that attacks the brain and spinal cord. It’s highly contagious and can cause symptoms that range from fever and headache to paralysis.

Polio vaccines have been around since 1955 and — after mass vaccination programs — have stopped the spread of polio in the United States. The IPV vaccine is used in the United States for polio.

Here’s more about how it works, when it’s typically given, and what you can expect after vaccination.

IPV stands for inactivated polio vaccine. This means it contains poliovirus that has been killed off.

The vaccine must be given in a series of four shots to boost protection. It is given as a shot in the arm or leg, depending on a child’s age. The series is usually given before a child starts kindergarten in the public school system.

Before Jan. 1, 2000, the oral poliovirus vaccine (OPV) was the route of vaccination for polio. It involved swallowing a small amount of live virus. Though the vaccine was (and still is) very effective, it caused a small percentage of children (1 in 2.4 million) to develop polio.

Now that the virus is well contained in the United States, experts have eliminated any risk of transmission and switched to the IPV vaccine. The OPV vaccine is still used in other countries.

The IPV vaccine is 99 percent effective. This means that out of 100 children fully vaccinated with the IPV vaccine, 99 will have protection from the virus.

Even just 2 doses of the vaccine provide 90 percent protection. Three doses get this number up to 99 percent or better. The Centers for Disease Control and Prevention (CDC) recommends getting all four doses in the series for the strongest protection.

Vaccines against polio have been so effective that the virus has been eliminated in most parts of the world. For instance, in the 1950s, the United States had more than 15,000 cases of polio. By the 1960s, vaccination brought this number down to under 100. And there were fewer than 10 cases of polio by the 1970s.

Polio is now found mostly in Pakistan and Afghanistan.

The CDC recommends the IPV vaccine for all people in the United States. The vaccine is given in four doses, typically at:

  • 2 months
  • 4 months
  • 6 through 18 months old
  • 4 through 6 months old (booster)

If a younger child travels to a country with high transmission of polio, there is also an accelerated dose schedule available.

What about adults?

Most adults have likely been vaccinated against polio in the past, as it is required to attend public school. But the IPV vaccine may be given again under certain circumstances:

  • if you need to travel to specific regions where polio is common
  • if you work in a lab that handles poliovirus
  • if you regularly treat polio patients in a healthcare setting
  • if you are unvaccinated and your child (for example, an international adoptee or refugee) is receiving the oral poliovirus vaccine

If you meet these high risk criteria, you may receive the vaccine on its own or in combination with other vaccines.

For adults, the vaccine is given as a three-dose series:

  • the first dose at any time
  • the second dose 1 to 2 months later
  • the third dose another 6 to 12 months after the second dose

Who should not get the IPV vaccine?

The IPV vaccine is safe for most children and adults.

That said, be sure to talk with a doctor if you have concerns about an allergy to the vaccine’s ingredients.

You should also not get the vaccine if you’re moderately or severely ill, though getting it when you have a more mild illness, like the common cold, is considered safe.

Pain or swelling around the injection site is a possible side effect of the IPV vaccine. There may also be a visible or red sore spot after your vaccination.

If you have a history of allergic reactions, there is a small possibility you may have a severe reaction to the vaccine. Call 911 immediately if you experience any signs of anaphylaxis, such as:

  • trouble breathing
  • rapid heartbeat
  • dizziness
  • hives
  • facial or throat swelling
  • weakness

Also, let a doctor know if you experience any dizziness, vision changes, or ringing in your ears after you’ve had the shot.

If you have questions about the IPV vaccine or how it might affect you or your child, consider calling a doctor to go over the benefits versus the risks.

If polio is eradicated, do you still need the IPV vaccine?

Part of keeping the virus at bay is mass vaccination. It takes just one person with a virus to begin the spread to many people, as the United States has seen with COVID-19. Keeping immunity levels high through vaccination — in this case, with the IPV vaccine — prevents this spread.

Should adults get vaccinated?

Most adults have already been vaccinated against polio, though experts do not know how long protection lasts.

If you have not been vaccinated in some time and are at higher risk — healthcare worker, laboratory worker, traveling to an area of high transmission — speak with a doctor about getting vaccinated.

Can the IPV vaccine cause polio?

No. The IPV vaccine contains inactivated poliovirus, which means the virus has been killed off and cannot infect and cause illness.

Why did the U.S. change from OPV to IPV use?

First, the OPV vaccine carries a very small risk of transmitting polio to people because it contains a live virus. Second, the IPV vaccine is as effective at preventing polio as the OPV vaccine. Also, the CDC says the decision was also made based on the very low rate of polio coming into and circulating through the United States.

Polio has not been seen in the United States since 1979. Control of the virus has been achieved in large part due to mass vaccination. The IPV vaccine is considered safe and is recommended by the CDC for all children and adults in high risk settings.

Experts do not know how long protection lasts, so you may need to be boosted depending on different factors in your life, like travel or work. If you have questions about the vaccine and whether you need it, contact a doctor for more information.