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Understanding polio

by Tshepy Matloga-Malope
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Poliomyelitis (Polio), is a highly infectious disease that mainly affects children below the age of 5 years. Although it has largely been eradicated due to vaccination efforts, the threat of polio still lingers, making it crucial to understand the significance of continued vaccination. By Tshepy Matloga-Malope

The dangers

Polio is mostly spread through the faecal and oral routes, largely through unclean water and poor sanitation.

The disease can cause paralysis, disabilities, and, in extreme instances, even death. There is no cure for polio, and it can only be prevented by immunisation. Treatment for acute polio generally focuses on limiting and alleviating symptoms.

Those with paralytic polio may require long-term physical therapy and assistive devices, while specialised equipment is required for those needing breathing support.

The World Population Review, reports that the annual number of cases has dropped by more than 90% since 1988.  In fact, globally, only 6 cases were reported in 2021, which is a significant reduction from an estimated 350 000 cases recorded each year in the late 1980s.

Today, polio is endemic in only two countries: Pakistan and Afghanistan.

In February 2022, Malawi confirmed its first case of wild-type Poliovirus in 30 years imported from Pakistan; eight cases followed in Mozambique months later.

Although no further cases were reported after intensive vaccination campaigns were immediately conducted throughout Southern Africa, it is clear how easily this virus can spread.  Until the transmission of the polio virus stops in both Pakistan and Afghanistan, all other countries remain at risk of importing the virus, especially where vaccine coverage is inadequate.

South Africa was declared polio-free on October 20, 2006, and no new cases of wild-type Poliovirus have been reported since.

However, with the imperfect vaccine coverage, especially since the COVID-19 pandemic disrupted vaccine services, Dr. Edina Amponsah-Dacosta, who is a medical virologist and vaccinologist at Vaccines for Africa and the School of Public Health at UCT, said the risk of importation remains high and therefore stressed the importance of vaccination.

“We recommend that parents take their children to catch up on any vaccination they might have missed to reduce the likelihood of infections from any vaccine preventable diseases, including polio,” she says.

MORE HERE on post-birth vaccinations

The history of polio vaccines

The first Polio vaccine was developed in the 1950s by an American physician, Dr. Jonas Salk, and is currently available as Salk Inactivated Poliovirus Vaccine (IPV). In the early 1960s, four new Poliovirus vaccines were developed so it has been around for a very long time!

Type 1 and 2 monovalent oral Poliovirus vaccines (mOPV) were introduced in 1961, followed by type 3 mOPV in 1962, and then the trivalent oral Polio vaccine in 1963, which is no longer in use. South Africa provides routine polio vaccinations free of charge through the national expanded program on immunisation.

The regimen is as follows: Oral Polio vaccine (OPV), given as drops by mouth at birth and again at 6 weeks of age, Inactivated Polio vaccine (IPV) is given via injection at 6, 10, and 14 weeks and then later at 18 months of age.

The IPV comes in a combined formulation with the vaccines against diphtheria, pertussis, Haemophilus influenzae type B, and hepatitis B.

Why it is still important to vaccinate

There is no cure for polio, so preventing it through vaccinations remains our most effective public health measure against the disease. The oral polio vaccine contains an attenuated (weakened) vaccine virus, which activates an immune response in the body.

When a child is vaccinated with OPV, the weakened vaccine virus multiplies in the body for a limited period, long enough to build protective antibodies.

During this time, vaccine viruses can also be excreted. In areas with inadequate sanitation, the excreted vaccine virus can spread in the immediate community, offering protection to other children through passive immunisation before dying out.

“However, if populations are under-immunised, an excreted vaccine virus can continue to circulate for an extended time.

The longer it is allowed to survive, the greater the chance of mutation. This mutated virus, known as the circulating vaccine-derived poliovirus (cVDPV), can cause paralysis in unvaccinated individuals. Cases of cVDPV are rare and, with optimal vaccine coverage, can be avoided altogether,” said Dr. Amponsah-Dacosta.

She also emphasised the importance of completing the number of Polio vaccine doses.

“Completing the number of recommended doses of the vaccine protects you from contracting Polio as the immune protection provided therein against paralytic disease is lifelong. A complete schedule of polio vaccination is 99% to 100% effective against paralytic polio,” she says.

In conclusion

Polio remains a significant public health concern despite significant progress in its eradication.

The risk of contracting the polio virus remains high among those who are not vaccinated. While South Africa is polio-free, the high degree of international travel to and from endemic countries increases the potential for importation. Sporadic outbreaks such as the recent ones experienced in neighbouring countries only further heighten this risk.

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