Polio and Monkeypox Are Circulating—Am I Protected?

With polio found in the wastewater in both London and New York City, many adults are wondering what their polio immunization status is. Will childhood vaccines continue to protect against the circulating strains? How does one even begin to locate vaccination records? Is it safe to just get a boost if in doubt? While the task of checking the family’s vaccination records may sound daunting just as the school year is starting, it is worth taking stock and getting needed updates.

What strains of poliovirus are covered in the vaccine?

There are three strains of polio: wild types 1, 2 and 3. A vaccine against all three types of polio was created in 1955, called inactivated polio vaccine (IPV), which was given as an injection. In 1961, oral polio vaccine (OPV) was developed and given as drops in the mouth. Due to its convenience, the vaccine of choice soon became OPV.

However, the weakened version of the virus used in OPV can go through changes as it passes through the intestine making it possible to revert back to the wild type which can cause paralysis. This happened once per 13 million doses in the 1990s in the US. By far the most common circulating vaccine-derived polio virus was type 2. Although the risk of paralysis from OPV was very rare, as types 2 and 3 were eradicated, the need for a safer vaccine became evident and the US switched to the injectable IPV in 2000.

Elsewhere in the world, OPV continued to be used due to its convenience and the importance of vanquishing polio. When type 2 was declared eradicated, the global supply of OPV gradually switched to a bivalent form containing only types 1 and 3. This means that people vaccinated abroad may be susceptible to vaccine-derived type 2 polio virus. This is the type found in the sewage in London and several counties in New York and New York City, prompting health officials to get children up to date on polio vaccination. In some areas, vaccine coverage is very low, allowing polio to circulate.

How do the polio vaccines work?

Polio is transmitted via the fecal-oral route, such as by contaminated water or soiled hands. Once in the intestinal tract, the virus replicates and can gain entry to the nervous system where one in 200 cases can result in paralysis. In 1921, Franklin D. Roosevelt contracted paralytic polio when he was 39, but still went on to become the 32nd US President twelve years later.

To interrupt polio transmission, the virus must be stopped in its tracks in the intestine. Although the IPV vaccine is very good at preventing paralytic polio by providing systemic protection, only OPV primes the intestine to develop antibodies against polio. This priming is called “mucosal immunity” and is part of why OPV was a mainstay of the polio eradication effort throughout the world.

How many doses should children and adults have?

Polio vaccination requires four doses for children who start the series before four years of age. People who are unvaccinated should receive three doses if starting after four years of age. Adults who only received one or two doses should finish the series—it does not matter how long it has been since you were last vaccinated. Adults who are traveling to places with a high polio incidence and have already finished their polio vaccination series can talk to their clinician about getting one lifetime booster.

How and where do I check my immunization status in the US? Does my physician hold all the routine vaccination records?

Pediatricians often provide a vaccination booklet for parents to record immunizations for their child. Your parents may still have a copy of your records or may have taken a picture of it at one point. It is worth checking the family archives for important records like these. Your records may have also been entered into an electronic reminder system to allow the clinic staff to send a reminder for additional vaccines or boosters. If you have moved frequently, you can begin consolidating records by reaching out to the state department of public health to see if you can request your records.

I’m fully vaccinated against polio but am still worried. How long does my childhood vaccine last?

Two doses of IPV are 90% effective against paralytic polio, and three doses are 99-100% protective. You are considered fully vaccinated and protected with four doses of any combination of IPV and OPV (administered in the US before 2000). The last dose should be at least six months after dose three, and should be given after four years of age.

Do I need to take any tests to find out if my immunity after vaccination in childhood still works for certain diseases, such as polio or measles?

The Advisory Committee for Immunization Practices (ACIP) monitors the incidence of disease, vaccination practices around the world, and provides recommendations to doctors about the best strategy to protect children living in the US. The ACIP recommends that if vaccination records are unavailable for children 18 years or younger, the child should be vaccinated or re-vaccinated according to the current schedule. This is because the laboratory tests needed to assess immunity against all three strains of polio are increasingly unavailable. This is because wild polio type 2 was declared eradicated in 2015, at which time only certain labs began handling the antibody tests as the live virus was consolidated and destroyed to prevent re-emergence.

For other diseases like measles or smallpox, antibody testing is possible but may not be covered by insurance. In some cases, it is wisest to be revaccinated. This is a conversation that would be important to have with a clinician.

Routine vaccination against smallpox ended in the US in the 1970s. This vaccine was administered by dropping the vaccine virus on the upper arm then using a two-pronged needle to puncture the skin, leaving a scar at the inoculation site. Adults over age 50 may still see a scar on their upper arm suggesting receipt of smallpox vaccination. People who are expected to have occupational exposure to smallpox can discuss vaccination or boosting with their healthcare team using newer vaccines delivered by injection. These vaccines also protect against monkeypox, but due to scarcity of the vaccines eligibility is limited to those most at risk.

How do I remember my immunization schedule?

The schedule for adult vaccines in the US follows CDC recommendations based on age and health conditions which may put a person at higher risk for serious disease. If you are about to turn 50, or just recently celebrated this milestone, check your vaccination records. If you have children, the back-to-school flurry may be a good time to take care of your own health needs, too. Many local pharmacies can provide needed vaccines, making it easy to not only get needed immunizations but track them, too.


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