How the body responds to a vaccine with Doctor Teresa Lazzaro

00:00 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.  

00:25 Rachael 

Hi everyone and welcome to The Vaccine Coverage, our podcast where we explore everything about vaccines and immunisation. My name is Rachael McGuire and I’m joined today by our very special guest, Dr Teresa Lazzaro. Welcome, Teresa, are you able to introduce yourself to the audience?  

00:40 Dr Teresa Lazzaro 

Hi. I’m Teresa Lazzaro. I’m a paediatrician. I’ve been very fortunate to have a long experience working in a specialised immunisation service over the last 25 years. 

00:52 Rachael 

Thank you so much for joining us. We’re really thrilled to have you here. I wanted to pick your brains today and talk about what actually happens after you have a vaccine. So, whether a vaccine is given by a needle, often in the arm or in the leg, if you’re a little baby or by mouth, can you tell us how the body might respond to that?  

01:08 Dr Teresa Lazzaro 

So when we give a vaccine, we’re trying to copy in a very safe way what happens when you have a normal or natural infection with a virus or another bug. If you think about if you get a cold or another infection, you usually start to feel a little bit unwell, you might have aches and pains, you might have a fever or a temperature, and that’s a sign that your body is responding to that infection and producing antibodies, which are chemicals to fight off the infection. So when we give you a vaccine, we’re actually replicating that process. So it’s normal to feel tired, a little bit unwell, have aches and pains and have a temperature. In fact, they’re not side effects. It’s a normal process which shows that your body is responding to the vaccine and making antibodies which will protect you to the real infection.  

02:01 Rachael 

So you’re saying that sometimes when you experience these sorts of, well, people call them side effects, they’re not necessarily a bad thing. It just shows that the vaccine itself is working in your body. And do they always occur after a vaccine has been given, or some people don’t get these sorts of experiences? 

02:17 Dr Teresa Lazzaro 

So not everyone will experience these reactions, but it’s pretty typical to have, well, not even a reaction – the response – to have some sort of a response post a vaccine, even if it’s just a sore arm or feeling a little bit tired. Now, when you’re a small baby, you can’t tell people that your arm is sore or that you’re tired. So you may be sleepier, or not as active. You may not feed as much. Or you might cry, and that’s telling your parents that you’re sore or unhappy, but not really where or what’s happening. But that’s how young babies communicate.  

02:53 Rachael 

And so, I guess as a new parent, seeing your child experience those sorts of things, that crying, that fever that I guess irritability, for a new parent that could be quite frightening to witness. What’s your advice for parents who are getting their children vaccinated? Do they need to worry about this or what do they do? 

03:12 Dr Teresa Lazzaro 

So, I think what you’re seeing is relatively mild. By relatively mild the baby’s feeding, enough to have wet nappies, is waking, you know, for most feeds. And it’s not crying for hours or out of control or very high pitched. If you’re seeing something that worries you, I always tell parents ask someone. Get it checked out. Talk to, perhaps someone in your family. Talk to Nurse On Call. Talk to your GP. Give some Panadol if the baby is very irritated. If the symptoms are things like vomiting and diarrhoea, you really should seek help if you’re concerned that the baby’s not taking in enough fluids or really losing too much fluid from diarrhoea, and you should seek medical advice then.  

03:57 Rachael 

If we have a think about that sort of vomiting and diarrhoea type of side effect, you know, certainly with vaccines that are given by the mouth, that can be one of those side effects. Can you explain how that happens? Is that the vaccine working in the gut and that’s what’s triggering it?  

04:13 Dr Teresa Lazzaro 

So there is a vaccine which is given at two and four months in most of Australia, which is the Rotavirus vaccine, and that vaccine is what we call a live vaccine. It has a virus which is not the real rotavirus. It can’t give you the real disease but has been changed so that it will give you the rotavirus infection in a safe way. But we’re giving you a very mild form of gastroenteritis infection, which is what rotavirus is. So, most children won’t have any significant effect from that vaccine, but some children will have loose stools or diarrhoea, or have vomiting. Mostly it will be very mild, sometimes, as I said before, if the child’s not drinking enough or losing too much fluid through diarrhoea, or it’s lasting too many days in a small baby, that can be a concern and you should seek some help. Now that might be just things like giving some more fluid or some specialised fluids when children have gastro. Or it might be doing nothing extra. But if you’re concerned, or the baby’s very lethargic, you should seek help.  

05:19 Rachael 

So really, with that response, the main thing with that, and that parents need to be, you know, really conscious of is just making sure that what they’re losing isn’t more than what they’re taking in, so they’re feeding enough to keep them going.  

05:32 Dr Teresa Lazzaro 

Yes, absolutely. And that they have enough wet nappies. And that the baby’s not too irritable, which is another reason to seek help, and most children will not be too irritable.  

05:42 Rachael 

If we have a think about those injected vaccines and I think you touched on this earlier with that sort of red, sore injection site, why does that happen after a vaccine?  

05:52 Dr Teresa Lazzaro 

A sore injection site can happen after any needle that you have, it doesn’t need to be a vaccine because we’re actually poking something sharp through the skin and injecting some fluid. So it can just be an effect of forcing fluid into a spot where there shouldn’t be any additional fluid. So, can be what we call a local traumatic effect, or it can be a local reaction of the cells to the components of the vaccine. Now, that’s not an allergy or a dangerous response to the vaccine, but it’s just local cells in the muscle area responding to those vaccine components and that can cause redness or swelling, which can last for a few days or sometimes longer as a little lump under the skin. When should you be concerned? If the swelling is extensive, really covering most of the upper arm or there’s problems in the skin over the swelling. Or if the child or adult is experiencing significant discomfort or pain from the swelling.  

06:53 Rachael 

So if that was to occur and it was obviously concerning you, just go to your GP?  

06:58 Dr Teresa Lazzaro 

Always start with simple things. A cool face washer over the site. Some Panadol, reassurance, wait. If it’s still serious, I would start with the GP. Very severe reactions are uncommon. They can come up one to two days post a vaccine and usually resolve within a few days without any specific treatment and are not a contraindication to further vaccines. In very severe reactions, we would tell families that there’s a 50% chance of another very severe reaction, but they are very rare. There and those sort of reactions should be seen by a specialist service before proceeding. But most minor reactions can proceed without concern.  

07:38 Rachael 

Another side effect is fainting. Can you sort of talk us through fainting and what the process is there? 

07:45 Dr Teresa Lazzaro 

Yeah, fainting is a very interesting experience, if you’ve ever fainted. It’s a very scary experience for the person fainting and for the onlookers.  

07:52 Rachael 

For the person watching as well, yes.  

08:01 Dr Teresa Lazzaro 

And so fainting occurs for lots of different reasons, but it’s a response to a drop in blood pressure, which makes your body fall to the ground so that your blood pressure can equalise and blood can go to the brain. Now people can faint from pain. People can faint from a fear of pain or an anticipation of pain, and sometimes having lots of people around you who are very anxious and nervous increases the rates of fainting like groups of teenagers, something about the group effect and the fear effect.  

08:25 Rachael 

Watching someone else do it. 

08:26 Dr Teresa Lazzaro 

Fainting is very rarely a serious reaction to vaccines. There are very rare individuals, perhaps one in a million, who would have overwhelming allergy and as an end stage of that allergy where your heart is affected, you would faint. But that usually comes with other signs, such as a rash, respiratory problems or breathing problems, nausea and vomiting, or other features of severe allergy. It doesn’t occur as a first event, so fainting in itself is usually never a sign of a serious vaccine reaction. Having said that, very young babies can have a rare reaction where they do drop their blood pressure, post vaccines and become pale and unwell and have a fainting-type episode. But again, it’s a rare reaction in infants.  

09:15 Rachael 

So we have that sort of infant version of a faint that’s not necessarily linked to a certain vaccine. Again, it’s just the process of being immunised.  

09:24 Dr Teresa Lazzaro 

Yeah, it’s a really rare reaction that happens in children under one. It can happen with any of the vaccines under one year of age. It’s a good news type of reaction because it’s not linked to increase in death or serious illness. And the babies naturally recover, although it can look very scary for parents and most parents would seek medical advice. The fainting response in older children and adults, we can help that group have vaccines safely by lying down where they won’t drop their blood pressure. Or if there’s great fear or anxiety, there’s medicines and other things that we can do to try and relieve that anxiety and also take them out of that group situation and vaccinate them individually, where their fear and anxiety might be less.  

10:09 Rachael 

So really that environment plays a part into that older group who might experience fainting.  

10:14 Dr Teresa Lazzaro 

Absolutely. And the position. Get them lying down.  

10:16 Rachael 

Yeah, fantastic. Adults can also experience side effects, not just children. I think when we talk about vaccines and immunisation, often the focus is on children and obviously you’re a children’s doctor. But in adults they do also experience side effects. Is there anything that adults need to be aware of? 

10:33 Dr Teresa Lazzaro 

Usually adults and older people have less reactions than children, and they don’t usually mount high fevers. Children are more reactive and are more prone to developing a fever than adults, although adults can also develop fevers. So again, there is a really rare occurrence of serious side effects like overwhelming allergy, which can occur in adults post vaccine, which is why you should always wait after a vaccine and not get in your car and drive on the freeway, just in case you do have a reaction, even though you may have had a similar vaccine in the past, such as influenza vaccine. So we always tell people to be aware of allergy. How do you know you’ve got an allergy? Again, we look for features like an immediate rash, which is usually a rash like mosquito bites or lumpy rash, breathing difficulties, feeling unwell, vomiting, diarrhoea, but really feeling overwhelmingly unwell very quickly in the first sort of half an hour post a vaccine. Otherwise, adults can have similar responses like young children, where your body is just responding to the vaccine how we want it to. So it will make protection in the future. So, feeling unwell, lethargic, fevers, and also local reactions at the site where you may have a sore arm. Everybody remembers having a tetanus vaccine and having a sore arm. And sometimes we see lumps and redness like an injection site reaction in young children.  

12:01 Rachael 

So knowing that side effects following vaccines do occur, I guess that might make someone a bit more cautious to proceed with being vaccinated. What are your thoughts on that? And I guess, how do you advise people?  

12:12 Dr Teresa Lazzaro 

So what we like to talk to people about with any treatment or medication or procedure is, is the benefit of whatever you’re doing greater than the risk of not doing it? So there’s some very concrete examples of that. So for example, if you have a cancer and you don’t treat the cancer, the cancer will spread. So obviously the benefit is greater, you know, it’s a very concrete, simple thing. But it’s much harder when we’re talking about preventing an illness when you don’t actually have an illness. And I think there’s two components to this. One is, what’s the benefit for the whole community that you live with and what’s the benefit for you as an individual? So, we know a lot of families that I speak to say that the diseases that we vaccinate for now are very uncommon and that there is not a high risk of getting these diseases in a clean, wealthy society like Australia. And I’d have to agree with them in many ways. Although what I explained to families is that many of the diseases that we vaccinate for still exist, even though they’re uncommon and they can be picked up from people who are not sick, so it’s not just avoiding sick people or, you know, staying out of big groups that can make your risk higher. That you can pick up diseases, for example, like meningococcal disease, which is a very uncommon disease, but a disease that will land 100% of infected people in hospital and has a high risk of complications. And you can pick up that disease from someone who’s carrying the bug in their throat who doesn’t know that they’re sick. So there’s an individual risk benefit. And then there’s the community risk benefit. And as a community, if our vaccinations drop below a certain level, the diseases unfortunately come back. 

14:00 Rachael 

So I guess it really is weighing up how likely it is to be exposed to that disease and the impact of that disease. As you said, with meningococcal leading to hospitalisation. And then I guess, comparing that with the likelihood of the side effects and the impact of those side effects as well.  

14:17 Dr Teresa Lazzaro 

So we usually think that the benefit is greater than the risk, the risk of serious side effects is very low, and that, particularly if you’re a very young infant under one and people often ask me this, why are we giving so many vaccines to the very young? And that’s because if you get some of these diseases, not just meningococcal disease, but some of the other diseases as a very young infant, your risk of hospitalisation, serious complications and even death is much higher than if you’re older. So that’s why so many are given in the infant period. Because your immune system is not well developed until you’re about two years of age, so you are at higher risk prior to that time. Parents asked me what should I do if I’m concerned that my child’s had a serious side effect and I always say talk to your healthcare provider about that and see where there’s any specific advice that you need to have at the time, or any treatment that your child needs. But also we’re very fortunate in Victoria and many other states that we have vaccine safety services which are there to take your reports of serious side effects, to gather them together to see if that’s a signal for serious side effects in other children and also to provide direct advice for you and your child, particularly around further vaccinations. And our Victorian safety service, which is called SAEFVIC, has a clinic where you can be seen if you’re needed to, and is certainly very interested and wants to hear about serious adverse events. Or adverse events that you are concerned about post vaccination.  

15:48 Rachael 

Very good to know. How can we know that vaccines are safe until years after they’ve been first used? 

15:56 Dr Teresa Lazzaro 

Well, we’re very lucky that we do have years of experience with many of the vaccines we use. Some of them have been around for many, many years. So we have good long-term data based on information over many years, we believe that the benefits of all vaccines that we have in our current schedule outweigh the risks, including any potential long-term effects. Of course, this can always be an individual discussion for families if they have further concerns.  

16:28 Rachael 

I guess before we go, we reached out to our audience and asked them to provide some specific questions that we might put to you now, if that’s OK, Theresa? So the first question that we had was why do they recommend paracetamol to children having the meningococcal B vaccine? Why is that so important?  

16:47 Dr Teresa Lazzaro 

So the meningococcal B vaccine is a vaccine that does give children, usually a higher fever than other vaccines. In some young children, when they have a high fever, they could be at risk of a condition called febrile convulsions. It’s uncommon, but can happen with a high fever, and we want to prevent that high fever leading to things like febrile convulsions. A high fever can also make you feel unwell and irritable, and so we want the children to be feeling more comfortable post the meningococcal B vaccine. And we know if we give paracetamol beforehand, and post the vaccine, that the rates of high fever will be much lower and the risks of a high fever will be much lower.  

17:31 Rachael 

Yeah, good advice. And I guess just on that convulsions can happen without vaccination as well. Any fever, isn’t it?  

17:36 Dr Teresa Lazzaro 

Absolutely, absolutely. They are relatively common in children under five. They can occur with any high fever, but sometimes it’s about the rate of rise of fever. So not necessarily the actual height of the fever, but how quickly it goes up. And they can happen with one infection naturally and not with another. So sometimes they can be unpredictable. And rarely, they can happen with vaccinations, with meningococcal B or with other vaccinations if you are prone to febrile convulsions. So fever in itself is not a dangerous sign in children, it means that your body is working to fight off infection or to respond to a vaccination in the way we want it to respond, but very uncommonly, fever can lead to febrile convulsions, if you have an underlying tendency to febrile convulsions.  

18:27 Rachael 

So another question from our audience was my child developed a rash after their 12-month vaccines. Was it the vaccine and are they infectious?  

18:36 Dr Teresa Lazzaro 

So there’s one rash that we know a lot about after the 12-month vaccines. In the 12-month vaccines, we’re giving you a vaccine called MMR, which is measles-mumps-rubella. This is another live vaccine which contains a modified form of the measles, mumps and rubella viruses. They are not the real thing that can give you the real disease but give you a modified form of the disease which is very safe. But you can get a response to these vaccines with some of the features of the real disease, in particular about 5% of kids will get a measles-type rash, fever, runny nose like a mild measles illness about 5 to 10 days post the vaccine. It’s a common, expected reaction, the children are not super unwell usually, you don’t need to treat it and it’s not infectious.  

19:29 Rachael 

Very good to know. Are some people more prone to getting reactions after a vaccine? 

19:35 Dr Teresa Lazzaro 

Look, I think it’s a very individual response and there’s really no way of knowing whether you’ll have more of a reaction to a vaccine than another person, before you have that vaccine. If you’ve had a previous reaction, so if you’ve had a fever or felt unwell or been irritable to a particular vaccine, it’s likely that you’ll have a similar response to a subsequent vaccine. But these responses are usually very mild. It can be treated with Panadol or just observed and would not stop us from revaccinating. The only exception is allergy. If you’ve shown features of an allergy and such as rash or respiratory problems and we give you the same vaccine again, your allergic response could be worse. So we’d always want to know if someone’s had those sort of symptoms.  

20:22 Rachael 

Thank you so much for sharing all of your knowledge and expertise with us. It’s been an absolute pleasure chatting. Thanks Teresa.  

20:29 Dr Teresa Lazzaro 

Thank you very much.  

20:30 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, mvec.mcri.edu.au and through our newsletter and social media profiles. You’ll find links to subscribe to our newsletter and 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.