What Is “vaccine-Derived Polio” and How Much Should You Be Concerned?
Polio has been nearly wiped out worldwide, but now, for the first time in nine years, a case has been reported in the US . The person is not vaccinated, but the strain with which he was infected belongs to the type of so-called “vaccination-derived” poliomyelitis. Let’s talk about what that means, because it doesn’t mean you should avoid the polio shot.
What is poliomyelitis?
Polio is a virus that causes no symptoms or mild flu-like symptoms in most people who contract it, but it can sometimes affect the nervous system and cause paralysis or even death.
Two polio vaccines were developed against it: an injectable killed virus vaccine in the 1950s and an oral attenuated live virus vaccine in the 1960s. (These are often referred to as the Salk and Sabin vaccines, respectively.) The global campaign to eradicate polio was launched in 1988, and as of 2021, there have been only six reported cases of wild polio infection worldwide.
Eradication means vaccinating people around the world, with particular attention to places where polio is still circulating. Since humans are the only species that can carry polio, the idea is to make everyone immune to the disease, and then it will have no hosts and become extinct. Of the three types of wild polio, two have already been eradicated.
What do vaccines do?
There are two types of polio vaccines and they are used in different parts of the world due to the different risks and benefits of each.
The inactivated polio vaccine (IPV) is the only polio vaccine that has been used in the United States since 2000 and is currently one of the routine vaccines given to infants here . This is the safest polio vaccine for the person receiving it because the virus is inactivated and cannot make you sick. The virus contained in the vaccine cannot be transmitted to other people.
The downside is that even if you are vaccinated, if you contract the polio virus, you are protected from the disease, but you can still pass it on to others.
Because of these pros and cons, it makes sense to use this vaccine in places where polio is not commonly found. You are personally protected from polio if the case reaches your area, but in a place where outbreaks continue, it makes more sense to use a vaccine that prevents transmission.
Oral polio vaccine (OPV) is used in places where polio is more common. It prevents transmission as well as infection.
It also has a bonus feature where your body can actually spread the vaccine virus to others, essentially vaccinating them as well. This can happen because the virus in the vaccine is “live” but weakened. In addition to convenience, it is easy to manage. You don’t need a healthcare provider who knows how to give injections; you just need someone to squeeze a few drops of the vaccine into your child’s mouth, or even put the drops on a piece of sugar for him to eat.
Since this vaccine uses a live attenuated virus, it is dangerous for immunocompromised people. And because it can spread, it’s also not recommended for people in their home.
However, there are several other important risks associated with OPV, which is why it is avoided in places where there is no endemic polio. One is that, in very rare cases, the vaccine virus can cause paralysis (called VAPP for vaccine-related paralytic poliomyelitis). This is estimated to be one in every 2.4 million vaccine doses administered, or 0.00004%.
Second, again in rare cases, a vaccine virus can mutate and become capable of infecting humans. This is the so-called vaccine-derived poliomyelitis. People who have been vaccinated are still protected from vaccine-derived polio, but it can be transmitted to unvaccinated people.
How can vaccine-derived polio be avoided?
It’s simple: make a polio vaccine.
Remember that people who are vaccinated against polio are protected from it. If you get a full three-dose series of IPV, the vaccine that is used in the US, it will be 99% to 100% effective.
You are only susceptible to vaccine-derived polio if you are not vaccinated and exposed to the virus. For example, if you are traveling to an area where OPV is widely used, you should make sure you are vaccinated yourself. But even without traveling, you may come across someone who is a carrier of a vaccine-derived polio strain (for example, if they come from a place where this vaccine is used), and they can transmit the virus to you.
This is probably what happened with the case reported in New York. The patient was paralyzed and found to be infected with the polio vaccine strain. They were unvaccinated. The Rockland County and New York State Health Departments issued a statement recommending that “unvaccinated individuals, including pregnant women, those who have not previously received a polio vaccination course, or members of the community who are concerned that they may have been unprotected, be vaccinated.” “