What can I do to stop Poliomyelitis?
On 6 December 2019, the ministry of health of Malaysia confirmed that a 3-month old local Sabah male child was infected with vaccine-derived poliovirus type 1 (VDPV1) – the first case of polio in Malaysia after 27 years. As there is still no cure for this crippling and life threatening disease, the best weapon to fight polio is through preventing infection by immunising every child until transmission stops. Vaccine preventable diseases such as diphtheria and measles are making a comeback threatening the health of our nation, the children in particular, in the recent years. And this time is polio. It is timely for each one of us to understand what polio is and why polio vaccination is the best weapon against this dreadful disease. Let us all take our stand on promoting childhood vaccination.
What is polio?
Polio or Poliomyelitis is a highly infectious disease which can cause permanent disability and even death. It is caused by a virus which attacks the nervous system, the poliovirus. As a type of enterovirus, it can survive even the hostile acidic environment in the stomach. There are three wild poliovirus serotypes (PV1, PV2 and PV3). It is important to note that immunity to one serotype is not protective against the other serotypes.
Poliovirus spreads from one person to another through faecal-oral route. Polio affects mainly young infants and children under 5. During an infection, the virus enters the body through the mouth and multiplies in the intestine. The virus is then shed into the environment through faeces. An infected person is infectious immediately before and up to 2 weeks after symptoms appear. The virus can live in the faeces of an infected person for 4-8 weeks thus it can spread rapidly through a community, especially in areas with poor sanitation and hygiene.
Young children who are not yet toilet-trained are a ready source of transmission. Polio can spread through food or water contaminated by faeces. It has been reported that flies can passively transfer poliovirus from faeces to food. The duration between infection and initial symptoms is 3 to 6 days. The period between infection to the onset of paralysis is about 1 to 3 weeks.
Most people(9 out of 10 people) infected with poliovirus do not have any symptoms or very mild flu-like symptoms and are usually not aware that they have been infected. These people carry the virus in their gut and unknowingly spread the infection to thousands of other people before the first case of paralytic polio emerges. Thus, WHO considers a single confirmed case of paralytic polio as an epidemic.
A small proportion of people infected by poliovirus may develop initial symptoms such as fever, fatigue, headache, vomiting, drowsiness, stiffness over the neck and pain in the limbs.
Approximately 1 of 200 infections leads to irreversible paralysis. The lower limbs are involved more frequently, usually asymmetrical and sensation remains intact. This is caused by the viral invasion on the central nervous system. The virus destroys the nerve cells that activate muscles. As a result, the affected muscles lose their functions and the limb becomes floppy and weak. This condition is known as acute flaccid paralysis(AFP). All children under 15 years with AFP must be reported and immediately tested for poliovirus.
Between 10 to 15 people out of 100 people with paralytic polio, the virus attacks the nerve cells in the brain stem affecting breathing, swallowing and speaking capacity which is potentially fatal.
The scourge of polio does not end here. 40% of these paralytic polio survivors may go on to develop non-infectious post polio syndrome(PPS). The symptoms include new progressive muscle weakness, severe fatigue and pain in the muscles and joints. Why and how PPS happens is still not fully understood.
Several key risk factors have been identified as increasing the risk of paralysis in a person infected by polio. These include immune deficiency, pregnancy, removal of tonsils, intramuscular injections of medications, strenuous exercise and injury.
Poliomyelitis was once endemic in the world. WHO estimates that in the absence of vaccination, there would be 550,000 cases of children affected by paralytic polio every year. Polio vaccines were introduced since the 1950s. Global efforts to immunise children with the oral polio vaccine have reduced wild poliovirus cases by 99% since 1988 from an estimated 350,000 cases to 33 cases in 2018. Of the 3 serotypes of wild polio virus, only Type 1 is still in circulation while Type 2 and Type 3 were eradicated in 2015 and 2019 respectively. Attacks on vaccination programmes and, political unrest and wars are among the reasons why there are still pockets of wild poliovirus in the world. Polio is still endemic in Pakistan and Afghanistan (2019). International spread is a very real threat as majority of people infected by the virus do not have any symptoms and may not know they are carrying the virus. The best protection is to ensure a very high vaccination coverage among any population.
In Malaysia, oral live polio vaccine (OPV) was first available in the 1960s. Routine childhood immunisation started in 1972. Coverage for 3 doses of OPV exceeded 90% from 1991. The last major epidemic of paralytic polio was in 1977. The last local case of polio was in 1986. There were 3 imported cases of wild poliovirus in 1992. WHO declared the Western Pacific region, including Malaysia, polio free in October 2000.
There are 2 effective and safe polio vaccines, namely OPV and IPV. OPVs are the predominant vaccine used to eradicate polio. OPVs offer long lasting protection and is given as 2 drops into the mouth of a child. The weakened polioviruses contained in OPV are able to multiply effectively in the gut, get excreted and can spread to others in close contact. However, these attenuated viruses are about 10,000 times less able to cause paralysis. OPV builds protection in the child’s intestine. This vaccine not only protects the child but also protects those others around the vaccinated child. Virtually all countries which have eradicated polio used OPV to interrupt person to person transmission of the virus. OPVs are easy to administer in mass vaccination campaigns. A single dose is not protective thus several doses of OPV should be given to every child in places where polio is a threat.
Inactivated(killed) polio vaccine(IPV) is given as an injection and needs to be given by a health trained personnel. It is 5 times more expensive than OPV. IPV builds protection in the blood instead of the intestine. It helps to boost immunity against polio but it does not stop polio from spreading between children so it is not useful in places where the virus is still circulating. IPV is the vaccine of choice in polio-free countries. The Malaysian National Childhood immunisation programme introduced IPV in 2008 and was fully implemented by 2016.
However, in extremely rare cases, about 2 to 4 cases per 1 million birth cohort per year in countries using OPV, the live attenuated vaccine-virus in OPV can mutate and cause paralysis(vaccine-associated paralytic poliomyelitis or VAPP). If a community is seriously under- immunised, an excreted vaccine-virus maybe able to circulate in the community over a prolonged period of time uninterrupted, it can undergo genetic changes and over a course of 12 to 18 months, reacquire its natural ability to cause paralysis. This is known as a circulating vaccine-derived poliovirus(cVDPV).
From over 10 billion doses of OPV given worldwide, there were fewer than 800 cases of cVDPV in 24 countries from 1988 to 2018. Within the same period, in the absence of vaccination with OPV, more than 1.5 million children would be paralysed by wild polio. Circulating VDPVs occur when routine immunisation activities are interrupted by poor acceptance as by anti-vaxxers leaving pockets of susceptible population. Hence, the problem is not with the polio vaccine itself but with the low vaccination coverage. If a population is fully immunised, the people will be protected against both wild poliovirus as well as the cVDPV.
The case of VAPP from Sabah was caused by cVDPV type 1. The WHO announced that this strain was genetically linked to the ongoing poliovirus circulating in the southern Philippines, which declared an outbreak of polio on 19 September 2019. This rare strain can occur only if a population is seriously under-immunised.
The young Sabah infant was not fully protected having just received 1 dose of IPV . Based on an investigation of a VAPP outbreak, the protection conferred after 1st IPV and 2nd IPV was 36% and 89% respectively. It could have been prevented if the community he was living in has a high immunisation coverage.
Surely, by now, these questions would be playing in your mind. Who made up the community he lived in and what were stopping the community from achieving a high level of protection? The community we live in is very important. As there are more and more marginalised people including the migrants in our country living in extreme poverty with health and social issues, what we see in Sabah can happen even in the other states. We want the government through the different ministries and not just the ministry of Health to review their policies and approach on not just the public health but also the economics, sanitation, transportation and the like for the benefit of the rakyat they serve. And as members of the human race, we each have our part in the fight against polio. Ask yourself,” What will I do to stop polio?”