Note: Today’s topic may look familiar. Sorry about that. Here is my take on a topic Steve covered yesterday.
The first American polio case since 2013 was reported last month in New York. The young adult had developed paralysis after contacting a strain of polio that was vaccine-derived. How this infection occurred, and how widely polio may be circulating is now under investigation, as paralysis is an uncommon consequence of the infection, which often has no symptoms. Evidence of polio’s spread was also detected in England in London’s wastewater, where there has been (to date) no active case detection.
Wasn’t polio eliminated in most countries decades ago? How did we get (back) here?
Throughout most of human history, poliomyelitis (polio) has been a cause of paralysis and death, with cases going back likely thousands of years. A viral infection of one of three different polioviruses, polio mainly affects children and is most often transmitted through sewage-containing drinking water. Most infections have no symptoms, so the disease can spread widely undetected. In some circumstances, the virus infects the brain and spinal cord, causing paralysis and sometimes death.
It was not long ago that polio was a feared disease, with surges leading to cities closing down gathering places like pools and theatres. The infection, which mainly affects children, can start with flu-like symptoms but every parent feared the potential for it to worsen – in some cases, leading to the inability to eat and even breathe. Treatments for polio were (and remain) supportive only. The iron lung (see above) used changes in air pressure to inflate and deflate the lungs. While many children could eventually leave an iron lung, not all could, and some spent their entire life in iron lungs. Even without the iron lung, children could face a life of partial or complete paralysis.
Dr. Jonas Salk developed the first vaccine, inactivated and injectable, in 1955 and countries began widespread vaccination campaigns. From almost 60,000 infection in 1952, infections in the USA plunged to under 5,500 by 1957. The oral (live) vaccine was developed by Dr. Albert Sabin in 1961 which became the preferred vaccination method. By the 1960s, polio was paralyzing fewer that ten Americans per year. The iron lung, which was a literal lifesaver a decade earlier, became obsolete.
Vaccination has virtually eliminated polio from the earth. The oral polio vaccine (OPV) became the preferred vaccination method after it was introduced. It contains poliovirus strains that have been weakened, in that they cannot cause severe illness, like paralysis. Because it is ingested orally, the antibodies it produces protects one from exposure to wild poliovirus in the event of future exposure. The inactivated polio vaccine (IPV) provides good protection against polio but this form of vaccination still allows the transmission of wild poliovirus, although the vaccinated individual will not themselves become ill. In the US and other countries, children receive the IPV at 2, 4 and 6 months of age, and again at ages 4-6 years.
The OPV is easier to administer and less expensive than the IPV and protects individuals and the community against infection (in the event the weakened virus is excreted and ingested by others, it can give immunity), which has been important in vaccination campaigns that seek to eradicate the disease. However, if vaccine uptake is low, the weakened but still viable virus can mutate, allowing it once again to cause paralysis. In the case of the New York resident that was identified with polio last month, the form of the virus was from the live vaccine which has not been used in in the US since 2000. Therefore, it is believed the virus originated in a country where the live vaccine is still used. This type of infection is exceptionally rare. In 10 years where 10 billion doses of OPV have been administered, fewer than 800 cases of vaccine-derived paralytic polio have been reported. Now there is a new OPV developed that will not lead to mutations that could cause polio, which could help play an important role in countries where the OPV is still used. Importantly, eradication of polio is within reach. With two of the three viral strains gone, only one strain remains, wild poliovirus 1. Polio circulation continues only in Pakistan and Afghanistan.
Pandemic effects on vaccination
The pandemic has had a significant effect worldwide on access to, and delivery of preventative health measures like routine childhood vaccines. With access to health care (especially primary care) restricted, and schools moving virtual, vaccination campaigns have been interrupted. This likely contributed to a recurrence of polio in Malawi, where a 3 year old child was paralyzed earlier this year, triggering a campaign to vaccinate nine million children in four countries.
Moreover, attitudes to vaccines may have changed because of COVID-19 vaccines. Pre-COVID, I would have expected the emergence of a safe and effective vaccine against a worldwide pandemic to reinforce how important vaccination actually is. But in some, the opposite has occurred, with hardened attitudes against public health measures, and especially vaccination – of any kind.
David Gorski noted recently how “new school” antivaxxers are increasingly indistinguishable from “old school” antivaxxers. If the endgame of the anti-vaccine movement is the elimination of all vaccine mandates, then even the high uptake and widespread protection we have against diseases like polio may be at risk. What a tragedy it will be if we ever see children in iron lungs again.