The Vaccine Coverage

Vaccines and the immune system with Doctor Linny Kimly Phuong

Published: 3 月 14, 2024
Duration: 22:24

Episode Notes

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The Melbourne Vaccine Education Centre (MVEC) is based at the Murdoch Children’s Research Institute. We are not-for-profit, and are supported by the Victorian Department of Health. We are verified as a reliable source of vaccine information by the World Health Organization through their 疫苗安全网.

This episode was recorded at The Royal Children’s Hospital Creative Studios with the assistance of Podcast Recording Services.

This podcast was made possible through the 2023 GSK Immunisation Award, presented at the Public Health Association of Australia’s (PHAA) Communicable Diseases and Immunisation Conference in 2023. MVEC has complete control over the content presented, and is independent of GSK and PHAA.

Episode Guest

00:03 MVEC credits 

You’re listening to The Vaccine Coverage, an educational podcast where we talk about the basics of vaccination in Australia, brought to you by MVEC, the Melbourne Vaccine Education Centre. The Vaccine Coverage is recorded and produced on the land of the Wurundjeri people. We acknowledge the traditional owners of the land and pay our respects to their elders, past, present and emerging.  

00:24 Rachael 

Hi everyone and welcome to The Vaccine Coverage, our podcast where we aim to share easy to follow information, debunk myths and discuss vaccines and immunisation. My name is Rachael McGuire and I’m joined today by a guru on infections; our very special guest Doctor Linny Phuong. Linny is a paediatric infectious diseases physician. In other words, she’s a doctor who specialises in treating children with infections. Welcome, Linny.  

00:49 Dr Linny Kimly Phuong 

Thank you. Thanks for having me.  

00:50 Rachael 

Thanks so much for joining us. Let’s jump right in. We can’t really talk about vaccines without talking about the immune system and immunity. So, can you start by explaining what is immunity?  

01:02 Dr Linny Kimly Phuong 

What is immunity?! So, not to start with any difficult questions or anything. Of course. But I think we should start off with. Yeah. What is the immune system? And perhaps we can go into immunity from there. So really, the immune system just to break it up is that there is an innate immune system and an adaptive immune system. And I think the way that I like to think of it and how I explain it to patients is that the innate immune system is very general and very non-specific. And then the adaptive immune system is very specialised and so has a more specific response to different bugs and germs. And so to go into those a little bit further. So, the innate system is very much about sort of the barriers that we have. So it’s the first line of defence. And I think of it is the gatekeepers of our body. The things that I think of are skin, you know, the things that coat our body. So sweat, tears, the acid that lines our stomach, mucus in our nose and, you know, lining our respiratory system. So when a germ tries to enter the body, the innate immune system is that first line of defence that kind of blocks the germ from actually entering the body. So the adaptive immune system is that specialised response that happens, and it’s something that actually builds over your lifetime. So the more you get exposed to things and we get exposed to millions and millions of germs every single day. Essentially your body is producing an adaptive immune response and that immunity that you were referring to. And so adaptive immunity is kind of made-up of lots of different components, but generally it’s kind of your B cells and your T cells, which are types of white cells and your antibodies that are produced by your B cells. So when your body sees a germ, what the body will do is that it will process it. So your innate immune system will do some processing to start with, and then it will pass it on to the adaptive immune system. So your B and T cells. Your T cells generally will produce a response, it might produce some chemicals and things to get the immune system stimulated. And then what happens is your B cells will actually form antibodies in response to the germ. And then it will also form what’s called memory cells and that gets stored away for later, which means that the next time you encounter that same germ or same thing that’s stimulated your immune system, your body will respond a lot quicker and a lot more efficiently.  

03:20 Rachael 

So one way that I explain it to my kids when we talk about the immune system, yes, my kids are nerds and we talk about the immune system. We actually call the B cells and T cells blood soldiers, and their antibodies are what they used to fight infections. Would you say that that seems about right?  

03:37 Dr Linny Kimly Phuong 

So The Bs and the Ts really come out to fight the infection once they’ve gotten past that first line of defence, which we talked about was, you know, skin and mucus and enzymes and all those other things that that are first line of defence. So the main difference between that general innate response to the adaptive and specialised response is that the specialised response takes some time. And so what we need to remember is that, because it does take time, if you are exposed to a certain germ before, it means that your body will respond a bit faster and more efficiently to that particular germ just to get rid of it and stop that infection from happening.  

04:17 Rachael 

So then with that in mind, why do we vaccinate? If your body is well equipped to sort of fight infections. What’s the purpose of vaccinating?  

04:24 Dr Linny Kimly Phuong 

That discussion is a really good segue to why we actually use vaccines and why we vaccinate. Vaccines are really used to train the immune system. We know that if you have had that exposure before in some way shape or form, it means that your body will respond faster and therefore be able to produce that immune response to kill the germ, the bacteria, whatever it is before it causes your full-blown symptoms. And so we talk about vaccines preventing disease, but we also talk about vaccines reducing the severity of a condition.  

04:58 Rachael 

When you look at the schedule of vaccines and they’re given at certain time points, what’s the benefit of sticking with that time point that they’re recommended?  

05:08 Dr Linny Kimly Phuong 

The National Immunisation Schedule is a really thought-out response into a program in terms of when you need to vaccinate against what diseases and so, for example at two, four and six months kids will often receive the same sort of combination of childhood vaccines and against certain illnesses that we know, in particular, kids are more prone to because they are more likely to carry those conditions. But also that they may have lost their immunity from their mothers at a certain point, and that’s when we would vaccinate against other conditions at, you know, 12 and 18 months, for example. Yeah. I think, with regards to when you vaccinate, it’s really about the epidemiology. And so the trends for when those diseases are more prevalent in those age groups. But also, perhaps when someone is more likely to be exposed to, to those particular diseases as well. Like for example the meningococcal vaccine that we give in adolescence is because we know that there’s a high rate of carriage in adolescents and therefore, we booster their protection at that time point.  

06:09 Rachael 

And by carriage you’re referring to someone’s ‘carrying’ that virus or bacteria or whatever you may be talking about. But they’re not necessarily experiencing symptoms. So, you don’t know that that person is sort of, able to pass that disease on to you, is that right?  

06:26 Dr Linny Kimly Phuong 

Yes, that’s exactly right. Exactly. And I think the other point is that we provide what’s called herd immunity. So we provide protection to the community. And this is particularly important for things like measles, for example. So, in Australia there is not a high level of measles, but we know that people travel overseas, and people come back from overseas and therefore we can get exposed to measles. Measles is one of those viruses that is highly contagious. And so, when there aren’t high levels of protection in the community, it can spread quite quickly. Because measles is the live vaccine, certain people in our population can’t receive that vaccine. So, you know, the very young. We’d be a bit more cautious in the older patients, but certainly immunocompromised patients can’t receive the vaccine. So, by us protecting the community and you know, ourselves and the community, it means that there aren’t those big outbreaks.  

07:17 Rachael 

So does that mean that not everyone’s immune system will function in the same way? There’s, I guess, specific things that can influence a person’s response to a vaccine, but also their risk of getting a disease in the first place. Can you talk that through?  

07:31 Dr Linny Kimly Phuong 

Absolutely. So the first thing to think is that, I always think about the newborn babies. So we know that when you were born, you have antibodies that you have inherited, I guess in a sense from your mother. So during pregnancy in the placenta, there is a transfer of antibodies from whatever mum has in terms of her protection. But also is boosted by any vaccines that she has during her pregnancy. So we know that as a newborn grows up, so once they reach about six months of age, a lot of that maternal immunity and the antibodies that they would have received start to, like, decrease. And that’s when it becomes really important that they’ve had some sort of, I guess, kick start to their immunity with their vaccines and that we start relying on that child’s own immune system to be able to fight infections. So I think that’s one aspect to it. So also when as we get older as we become unwell with various different things and our immune system is affected because of illness or because we go on medications for certain things. So certain patients might go on cancer treatments and that will affect their immune system. That would certainly affect their response to a vaccine because their Bs and T cells are really preoccupied, but also they are at risk of infections. So their first line of defence is down, as is their specialised adaptive immune system as well. So they are really prone to infections, but also because of the chemotherapy that they’re receiving; there are certain vaccines that they can’t receive. And so, what we often look at when we when we treat sort of more specialised cohorts of children for example, is what things are they going to be exposed to. So we know that before starting cancer treatment or chemotherapy we’ll look at what vaccines can we optimise beforehand to try and boost their immunity. We might also look at kids who, for whatever reason, don’t have a well-functioning spleen. What sort of additional vaccines might they need because they might be at further risk of certain types of bacteria. So often these patients will receive additional vaccines as well.  

09:34 Rachael 

And as you get older, your immune system, regardless of medications or what have you, its function does decline anyway, and that process is called immunosenescence. Can you talk us through that?  

09:46 Dr Linny Kimly Phuong 

Yeah, of course. So essentially immunosenescence is exactly as you described. So as you age, your immune system doesn’t function the same way when you get a vaccine. You might not respond in the same way and that you might not have that long lasting protection that you would if you were a younger, you know, 30 year old individual for example. And it just means that you are more likely to need more booster vaccines, so those extra shots to keep your immune system literally boosted. And in terms of your immune function, you like your cells might not be able to mobilise as quickly when you have an infection. So as much as possible, obviously we encourage people to have up to date vaccine status so that they are optimised in any way possible.  

10:31 Rachael 

So it really is those extra boosters, being up to date, but also recognising that there are specific vaccines that are for the older population which are stronger, so they’ll work better to promote an older person’s immune system.  

10:43 Dr Linny Kimly Phuong 

Yeah that’s right, exactly. So flu is a really good example of that. So we give it a different flu vaccine in older populations. There are also additional vaccines that we would recommend in older age groups. So for example, the shingles vaccine and yeah, as you said as you get older, your immune system changes and the function changes and the ability to respond to an infection changes. And so it’s kind of important to take into account and that’s why we, I guess have these recommendations and schedules.  

11:11 Rachael 

Yeah. So thinking back to before you mentioned a newborn baby might have some immunity from their mother. So antibodies are transferred over the placenta, you know, as they’re growing and then born. What about in breastfeeding babies? So do they get a transfer of antibodies then as well? 

11:28 Dr Linny Kimly Phuong 

Yeah. So there is certainly some antibody transfer via breast milk, but it’s less reliable and certainly it’s not as predictable. And so it’s not something that we would say if you were breastfeeding, then you your child would be protected, but certainly they are protected to a point. I think the other thing with vaccines that is really important is that vaccines are a controlled way of exposing an individual to an infection or a response, an immune response. We know through all the studies in the clinical trials that are done, what we expect to happen when someone’s been given you know this dose, for example, of a vaccine. Whereas if you are going out into the community and going to expose yourself to a condition like you just don’t know. 

12:11 Rachael 

There’s more variations to that sort of exposure. Yeah.  

12:14 Dr Linny Kimly Phuong 

Yeah, exactly. That’s correct.  

12:15 Rachael 

Yeah. So much harder to predict. I think we’ve covered lots of information there, going through the immune system and how vaccines work to prevent disease. Can we touch back on what actually is immunity?  

12:31 Dr Linny Kimly Phuong 

Yeah, sure. So I think to define immunity, it’s. I mean it’s a, it’s a big concept, but really broadly speaking its protection against a certain illness.  

12:41 Rachael 

So in summary, I think we’ve had a really good chat about what the immune system is, the purpose of vaccines and how to create immunity. I guess one thing I really wanted to explore was that vaccines can prevent infections, but then also reduce the severity of disease as well. Some of them I guess have, I guess a different goal. Can you elaborate on that?  

13:05 Dr Linny Kimly Phuong 

Yeah, of course. I think a good example is probably COVID infections. Even if you get vaccinated, you can still have COVID infection. But essentially, as I mentioned earlier, like we are training the immune system to be able to respond quicker and kind of have those protections in place. So that if you do encounter natural infection that your body is going to respond quicker and therefore you aren’t going to get those complications. And so, our primary goal really around COVID vaccination was to, I guess as much as possible, prevent hospitalisations and then prevent people from needing the intensive care unit. So I think overall it did that. 

13:44 Rachael 

And then if you think about COVID and compare that with, I guess, other illnesses like polio or even smallpox, where they are huge success stories. And not just reducing the severity of disease but preventing it from occurring altogether.  

14:00 Dr Linny Kimly Phuong 

Yeah, absolutely. Yeah, I think you’re right. So polio and smallpox obviously have been eradicated, well from Australia. We should be very local. But in terms of smallpox, obviously that’s completely gone. And that’s been as a result of vaccination very long time ago, it just essentially stopped this particular virus from circulating.  

14:21 Rachael 

So polio is a really good example of an infection that we don’t routinely see here in Australia, but it is found in other countries. So why do you think it is so important that here in Australia, we still continue to immunise against that disease?  

14:37 Dr Linny Kimly Phuong 

So I think as much as some of these conditions that we have on our National Immunisation Schedule are not seen in Australia, it’s really important that we continue to vaccinate against these conditions because there is always going to be international travel and so people are going to come in and out of the country. And so there is that risk that we might get exposed. And so I think we just need to be aware that these conditions are still an issue in places of the world. And so having that protection and vaccine against those conditions, it is important to kind of maintain.  

15:13 Rachael 

And I guess we need to look at how much disease we have in Australia but not become complacent by that. I think you know, just remembering the impact that those diseases can have, you know their outcomes on people’s lives, can be shocking. And so I guess, yeah, making sure that we stay up to date with our vaccines. Is so important.  

15:32 Dr Linny Kimly Phuong 

Yeah, I yeah, I think that’s a really good point because there are certain vaccines where perhaps the condition is so rare, but the consequences are so high that it’s really important to be vaccinated against those things.  

15:49 Rachael 

Before we finish up, I think I might just throw to our audience questions. If you’re happy to answer a couple?  

15:55 Dr Linny Kimly Phuong 

Sure thing. 

15:56 Rachael 

Is natural immunity better than vaccine immunity? 

15:59 Dr Linny Kimly Phuong 

I’m gonna say no to that, because I think on a on a very simple level, if you are exposed to a disease, you don’t know how severe your response is going to be and how your body will respond, and so you might have quite severe consequences from that condition. Whereas if you have vaccine- induced immunity then it’s really controlled. And as I alluded to earlier, like, clinical trials have kind of chosen like what dose and what frequency is needed to produce just the right amount of response. So that your body can kind of have that memory response and then respond properly next time if you are exposed to that disease. So yeah, so the answer is no.  

16:39 Rachael 

Do we really need vaccines when we can treat infections with antibiotics or prevent infections by wearing masks?  

16:46 Dr Linny Kimly Phuong 

So again, vaccines are really important so that we have that predictable response in terms of the body’s immune system and providing that protection. So vaccines will give the body protection so that when you are exposed to whatever condition it is then yes, it’s a bit more controllable. And yes, we can use antibiotics sometimes, depending on if it’s a bacterial or viral infection. Yes, you can prevent infections by wearing masks, but again, it’s not 100%. So masks are not 100% protective unless you’re wearing an N95 and or there are certain viruses that can get past that depending on other factors.  

17:24 Rachael 

And I guess on that there’s different ways that bacteria or viruses can be passed on. So it’s not always airborne.  

17:31 Dr Linny Kimly Phuong 

Yeah, that’s right. Exactly. We do things with our bodies from day-to-day and we expose ourselves in different ways to infections, you’re right. So certainly as you mentioned some conditions, some bacteria and viruses are airborne, some are droplets, so sometimes we will acquire an infection by, you know, touching infected surfaces or being exposed to snotty kids at daycare or there are certainly different ways that infection is transmitted. And so I think coming back to your question around why is vaccination important? Certainly, you are kind of training your insides and your adaptive immune system to be prepared for that insult, so that when it does come, your body is ready to fight infections, ready to produce antibodies and literally try and kill whatever germ is trying to, you know, invade your body.  

18:18 Rachael 

And I guess even if you are really vigilant with things like masks and all of that sort of stuff, behaviours change that and you can’t predict things like having an accident or cutting your leg or being exposed to things through your blood.  

18:34 Dr Linny Kimly Phuong 

Yes, yeah. Exactly. That’s right. And so yeah, again like it kind of speaks to the importance of vaccination. So tetanus is a really good example of that. So, you know, if you’re working in the garden, you know cutting your rose bush or, you know, something along those lines and you sustain an injury, then you’ve got your tetanus protection, hopefully, from your vaccinations to stop that from becoming a bigger deal than it needs to be.  

18:56 Rachael 

And another question, why is it that when you’re sick, you get swollen lymph nodes?  

19:01 Dr Linny Kimly Phuong

Yep. So that’s a that’s a really good question. So what your immune system does when you’re exposed to an infection is that apart from sort of processing what it is and then starting to respond, your lymph nodes are essentially where some of your Bs and T cells will sit, so your white cells will sit. And so they start to mobilise during an infection and so that they become, I guess, activity centres and they grow because they’re responding to an infection. And so certainly you will say if you’ve got a sore throat, for example, you might have swollen lymph nodes around your neck.

19:33 Rachael 

What is the role of the thymus? What is the thymus?  

19:37 Dr Linny Kimly Phuong 

Yeah, sure. So the thymus is a gland in the body, which is, I guess, part of the immune system. In that, so when I was talking about Bs and T cells before, so B cells are called B cells because they mature in the bone marrow and T cells are T cells because they mature kind of via the thymus. So the thymus, I mean is another component of the immune system and it is somewhere where these cells mature. And are able to produce that sort of long-term protection.  

20:08 Rachael 

So the spleen is another really important organ in the immune system. Can you talk about that?  

20:14 Dr Linny Kimly Phuong 

Yeah. So the spleen is another sort of component of the immune system. It’s essentially where a lot of our cells are, I guess, housed. And they are released when they need to be able to fight infection, and it’s also kind of the filter in the body. So just like the liver filters the toxins in our bloodstream, the spleen kind of has a similar role in that it is able to help respond to infections and release cells as it needs to. So the thing with the spleen, which is really interesting is that when you don’t have a functioning spleen, or if your spleen is removed for whatever reason, it puts you at risk of certain types of infections. And so people without a functioning spleen get additional vaccines as a result of that.  

20:54 Rachael 

And another question which you’ve kind of touched on throughout our chat. I’m on immune suppressive medications. Will vaccines work for me?  

21:03 Dr Linny Kimly Phuong 

Just because you’re on immune altering or suppressing medications, it doesn’t mean that the vaccines won’t work and it also will depend on what vaccines we’re referring to. So sometimes if you’ve got a suppressed immune system, you can’t receive certain vaccines, so live vaccines, for example, we would recommend against, but depending on your immune suppressant regimen and you know what type of medication it was. But on the other hand, being immunosuppressed might just mean that you need additional doses of vaccine just to kind of keep your levels up and to keep that protection going for longer.  

21:36 Rachael 

Thank you so much Linny for spending time with us today and sharing all of your expertise.  

21:40 Dr Linny Kimly Phuong 

Thank you for having me. 

21:42 MVEC credits 

This podcast was produced with the assistance of Podcast Recording Services. MVEC is a part of the World Health Organization’s Vaccine Safety Net. All members are verified by the World Health Organization as a source of reliable and credible vaccine safety information. MVEC provides vaccine education and news on our website, and through our newsletter and social media profiles. You’ll find links to subscribe to the newsletter and our social media profiles in the notes of this episode. MVEC also offers professional development opportunities for healthcare providers through our online education portal and our events. 



Education Nurse Coordinator, Melbourne Vaccine Education Centre

Rachael is a Registered Nurse and accredited Nurse Immuniser with a Graduate Certificate in Clinical Education. She has experience immunising at local council, travel clinics and hospital immunisation services, including SAEFVIC. Her special interests lie in vaccine safety, the immunisation of special risk groups and vaccine equity. In 2023, Rachael’s enthusiasm for public health led to her involvement in DFAT-funded projects in Lao PDR, providing education and support to improve decision-making around immunisation policy.