Health Matters with Daniel Martin. It's Health Matters. Welcome aboard, everybody. Thank you so much for joining me, Daniel Martin. Many of you would have heard about or read about on CNA.Asia how Singapore's confirmed one imported case of vaccine associated polio. It was an infant who was flown in from I came in from Indonesia and taken directly to NUH upon arrival in Singapore and then isolated upon admission.
We want to know more about why are we still hearing about polio and what is vaccine associated polio as well. I'm pleased to welcome Doctor Nicholas Chuu, infectious disease specialist, Fair Park Hospital, joining us on today's edition of Health Matters. It's been a wild off you. Hello, welcome back to the show.
Hi, um, yeah, so polio is a highly contagious virus that causes an infection, and really the, the concern is that the virus will infect the spinal cord, and this might lead to a severe disabling and also potentially life-threatening condition.
I was talking to some of my colleagues before the show began who are all very interested in this topic and they say, yeah, yeah, yeah, because they're of a certain age and they're like, I remember in the 60s and 70s, people were really affected by this and it was highly contagious. So it was highly contagious and it was preval not prevalent, but it was common in Singapore.
Um, well, the polio vaccine's been rolled out in Singapore since 1962, and, and obviously, it's, it's, it's taken off. It's not mandated by law, but I think the uptake is, is, is very robust in Singapore. And as a result, you know, we, we haven't seen any local transmission of, of cases since 1972.
So, in
fact, the last reported case was in, uh, 2006, and that was also an And uh imported case, same as the current one. OK,
so the full name for it is poliomyelitis. uh,
it's polio virus that causes a condition called poliomyelitis. So myelitis, uh, uh, uh, refers to inflammation of the spinal cord and therefore you get all the paralysis in your limbs and it could also, also affect your, your, uh, diaphragm, i.e. your breathing muscles, and that could impair someone's ability to breathe.
And how is it transmitted?
Um, well, polio is normally acquired through, through the oral route. So say if you have a patient who's contagious, they will be shedding the virus through their, their oral secretions. Then the virus kind of passes through your gut and it starts to replicate in the bowel. And because of that, your, your index patient will then start to secrete the virus in the feces.
So fecal oral transmission,
correct. So most likely this patient would, uh, well, I suppose this particular infant would be different, but, uh, in general for most patients, they would have acquired it through contamination of whatever. So
in the past, it could have been, yeah, through food prepared by people who've not washed their hands, for example, or I guess,
you know, sharing of saliva or respiratory secretions, for example.
It can be transmitted in the saliva and respiratory secretions as well. It's not necessarily just oral fecal transmission,
not necessarily. So if someone in the acute phase is infectious, uh, they will start producing the, the virus in, in their mouth as well.
I go for something to be transmitted so easily and to have such deleterious effects on the individual as well. No, no wonder the world celebrated when we so-called eradicated polio. Doctor Chu, why are we still talking about polio if we supposedly eradicated it?
Well, um, as of 2020, um, polio has been largely eradicated in most parts of the world, but what we don't know is that there are still 22 countries in the world where polio is endemic, i.e. Afghanistan and Pakistan, OK. Um, but the current imported case probably has, uh, uh, been the polio infection has been acquired as a result of, of vaccination potentially.
Let's talk about that. The articles are saying, um, vaccine associated polio. What is vaccine associated polio by definition?
Well, the, the WHO term for this is actually VDPV, which is vaccine-derived poliovirus. So to understand that, um, um, you need to appreciate that there are currently two types of polio vaccines. The first one is the oral uh vaccine, which is OPV or the inactivated vaccine, which is IPV, OK? Um, traditionally, we would have used the oral vaccine. Uh, for, and the oral vaccine remains the mainstay of
vaccination for large parts of the world. And the reason for that is because it's, um, you don't need to inject it. You just put it into an infant's mouth. So because of that, you get easier access, um, um, but the problem with the oral vaccine is that it's actually a live virus. It's a live attenuated virus, which means that the virus has been weakened. So in general, in, in uh uh a healthy uh infant, healthy host, um, the immune system will, will keep that under check.
So live attenuated the virus, the concept is I introduce a weakened form of the virus to your body and your body develops immunity against it.
It's almost as if you were, you were infecting somebody with, with polio, but because it's a weakened form, you're not likely to develop severe complications from it, OK? But the caveat to that is that if you use the oral vaccine in, in the live viral form in an immunocompromised host, what might happen then is this live virus might mutate. As it regenerates in the host, it may mutate and regain its virulence, i.e. its ability to cause the severe, uh, uh, downstream effects of polio. Oh
dear. And in this case, is that what we know that this poor infant received the oral form of the vaccine, i.e., um, the live attenuated form of polio, and is also immunocompromised.
Based on the information that is out in the public domain, um, it looks as if this, this infant is 5 months old, received the first dose of the polio vaccine in the, in the oral form at 2 months, and then at 4 months, received the inactivated form, OK? Um, and then symptoms may have begun at about 4 months of age. So the question is whether or not. Uh, because of the immunocompromised state, the initial dose of the live vaccine may have, you know, reactivated and caused, uh, paralysis.
Which form of the vaccine is utilized in Singapore for our children?
And in Singapore since 2021, uh, we have already phased out the oral form of the vaccine. So, i.e., we no longer use the life attenuated virus form. So it's all injected now and it's the inactivated vaccine.
OK, which still efficacious in terms of building up resistance to polio? Yeah,
of course. Um, so both vaccines have, have a high level of efficacy, although in the past, 1 may have argued that the oral form may have been more immunogenic, so, i.e., the amount of immune response that you get from the oral life form would have been slightly higher, but I think in general, the inactivated form, uh, for clinical purposes is highly effective.
How rare is this, doctor, this idea of vaccine-related um development, vaccine associated polio developing?
Um, well, if we're talking about paralysis as a result of polio from the, the vaccine, from the oral form of the vaccine, I think the recognized risk is about 1 in 2 million, so it's highly unlikely, but with an immunocompromised patient, um, you know, the, the risk is obviously much higher, but what we don't know is why this infant is immunocompromised, to what, to what degree of, of, uh. Uh, immune dysfunction this person has, and how did they
discover it? Because obviously, the first dose was the oral form, i.e. the, the live virus was given. So clearly at 2 months, they may not have recognized the immunocompromised state of, of the patient.
And it, it is possible that a parent might not know that their child is immunocompromised in some cases, is it? That's correct. OK, but that's a big umbrella term. Maybe if you can shoot out some examples of what we mean by the term immunocompromised because I mean, a listener might think it could be anything from Having asthma to having HIV. Do you know what I mean? So it's a very wide range.
Yeah. Um, well, for adults, in general, uh, causes of, of poor immune system could include chemotherapy for cancer, somebody with advanced HIV infection, uh, if they're on, uh, high dose, high-dose steroids, for example, for lupus, OK. But for, for somebody who's 2 months old for an infant, it's likely that the cause of the, the immuno compromised state may have been an inherited immunodeficiency problem,
something
that they were speculating because we don't have that information,
right, but that, but that is what we mean when somebody has an immunocompromised state, it means that therefore, um, it's affecting their own body's ability to respond to an infection. Correct. Got it. Now I wanna understand.
There are many things, obviously, a lot of people are wondering like, oh my goodness, poor thing, this poor child, what's the, but then there's also a group of people asking questions, especially in the comment sections like, oh, does this mean that with one imported case of vaccine associated polio, that this somehow increases the risk of community transmission in any way? What do we know about that? Because as I mentioned in my introduction, was immediately um taken to
NUH upon arrival and isolated upon admission. Obviously, our medical teams are wonderful and, and know their stuff and do their work very well. What is the risk of community infection? What do we know?
Um, well, in relation to Singapore, I think that the risk of community transmission is, is virtually zero, and the reasons for this are several fold. Um, firstly, the patient was admitted directly into NUH, so I think, you know, the duration that this patient. May have been in, in, out in the open, potentially shading the virus to the community is negligible. Secondly, the family members were here only for a brief period before the diagnosis was made and then they were quickly isolated and,
and screened as well. So again, um, the likelihood of them shedding the virus out in the community is unlikely. Thirdly, I think the level of sanitation in Singapore is first world, so it's again, uh, a factor in our favor. Um, and fourthly, um, as I said earlier, Singaporeans and Singapore residents are largely vaccinated against, uh, polio.
Are there multiple shots required for polio vaccination? I forget actually.
Well, in general, there, there are 5 for Singapore, but um other parts of the world may have only 4 shots that are required, but in general, you would give it to infants at age. 2 months, 4, and 6 months, and then again at 18 months and then probably at the end of the primary school years at about 11 or 12 years old. Got it.
OK. And the example that you mentioned of oral first followed by the uh non-oral version, that kind of combination approach is not practiced here in Singapore, right?
No, that's that's not the norm. I suspect what happened is that the, the uh Infant probably got the oral form first, and then they realized that there may have been a problem with the, the patient's immunity, then they switched over to the inactivated form,
potentially. Yes. Before we wrap up, let's spend a few minutes talking about what parents should be concerned about because I'm wondering whether the parents are reading the story, even though we've very clearly said how rare this case is and how the chances of it is something like 1 in 2 million as you described earlier on. Should parents worry for their own kids' safety when taking the polio vaccine?
Um, the form of polio vaccine that we use in Singapore is the inactivated form, so I would absolutely have, have no concerns there. Um, but on, on the flip side, I would be worried if a parent were to decide not to vaccinate their child because, you know, with, with Singaporeans traveling for holidays for work, um, that you may come into contact with, with somebody shading the polio virus overseas. So it's important that you get vaccinated.
And one of the things that I, I haven't mentioned earlier is that even though we think that wild type polio uh polio infections are largely eradicated in most parts of the world, um, one of the things that people don't know about is that, say in the last 18 months, OK, from early January 2023 up until the middle of 2024, uh, there have been multiple outbreaks of, of vaccine-derived um polio infections. So the WHO has recorded over 70 outbreaks. And
that's more than 1 in 2 million risk that I'm, I'm, that seems to buck the trend of the 1 in 2 million.
Uh, well, the, the, the outbreaks may not have led to paralysis, so essentially we're talking about people who have presented with uh a multitude of other symptoms that have been proven to be related to polio. So the reason for that really is because, um, um, all these countries would have relied on the oral form of the vaccine and. They would have had a lot of uh patients who are immunocompromised and continue to shed the virus as a
result of getting the live virus. And because if the uptake within your community, within your country is low, then the risk obviously of an outbreak is going to be much higher.
Would that not have contributed to the seesage, the cease of use of the oral version one would imagine?
Um, not, not necessarily, because if you can imagine. The inactivated vaccine would, would require the patient to be injected with a vaccine. Um, so obviously that adds to one level of complexity in order to, to be able to roll out your vaccine compared to something like a liquid that you just pop into an infant's mouth.
If you're talking about supply chains or chains to certain countries with lack of logistics or medical facilities, this all plays a part. Yeah. Got it. OK, final point, just a reiteration. I, I, I, I don't want people to start questioning something that's been around since 1978 and has served so much in terms of preventing disability and even death potentially from how serious polio was. Remind us why vaccination against polio remains our best events against a very serious illness.
Well, it's got to do with, with uh risk-benefit uh uh ratios. So I think even though the risk whenever you acquire polio, the risk of you developing paralysis is low. Um, But if you're unvaccinated, you're gonna put yourself, you know, at harm's way, um, in terms of the, of getting paralysis. And this paralysis is permanent. There's no treatment for it. Um, so once your arms or legs are disabled, you're, that's,
that's you for life. And also the fact that it's life-threatening if it affects your, your, your uh nerves controlling your breathing apparatus, then You know, we're gonna be in, in serious trouble that we cannot reverse.
And it's easily transmissible as well, unfortunately. We cannot afford a community outbreak and so it's wonderful that we do have in place um vaccination for everyone born after 1978. And that has played a big part in terms of keeping us polio-free to a large extent in Singapore. Doctor Chuu, it's been a pleasure. Thank you so much for speaking to my listeners today. Thank you for having me on again. My guest on the program, Doctor Nicholas Chou is an infectious diseases specialist
at Farrer Park Hospital. This has been Health Matters. I'm Daniel Martin for CNA 938. Before making any decisions based on the information in our program, please consult a medical professional.