[Music] None of the studies that were done subsequently found an association between MMR and autism. In a way, doing this studies is great because it proves again that the vaccine is safe and there is no issue. [Music] Birological with Florian Kramer. [Music] Hello and welcome to this week's episode of Birological. This episode was recorded on January 19th, 2026 in Vienna in Austria. So today we're going to talk about measles virus. Mises virus is part of the or to mix a virus family and part of the genus Morpili viruses. It has a number of close relatives that are animal viruses. So measles is strictly a human virus but there are very similar animal viruses and those include Rinderbest virus which used to affect cattle but was actually eradicated and also canin this type of virus which can be a problem in dogs and other animals. It's also more distantly related to very dangerous viruses like Nipoviruses and Hendroviruses but also to other common human pathogens like Mums virus and RSV. The virus has a single stranded negatively polarized RNA genome. It has a coding capacity of 16,000 base pairs approximately and the virus is about 100 to 250 nanometers in diameter. It's bleomorphic which means it doesn't have a very well-defined shape so it's kind of roundish but not very nicely round. That's true actually for most Pyramixivaruses they kind of look pretty ugly honestly. They don't have a very regular shape. They look like an ugly blob of a virus so you can hear I'm not a big fan of the shape and structure of Pyramixivaruses. When we look into how its structure looks like, how it's built, we have the genome on the inside that's protected by a nuclear protein. There's a polymerase associated to the genome and the phosphoprotein. And then the particle is stabilized on the inside by a matrix protein. Then we have a lipid envelope and we have two spike proteins in that envelope. One of them is called hemagglutinine and that is used by the virus to bind two cells. Then we have a second one that's called F-protein or fusion protein and that's responsible for fusing the viral membrane with the cell membrane which then allows to release of the viral genome into the cell and that starts the infection. They have protein pines to protein receptors on our cells, to the number of them. You don't have to remember that but one of them is CD46. Another one is CD150 and Nectin is involved in binding. So we see binding to a protein receptor and not to sugar receptors like with many other viruses. Inflants of, for example, pines to a sugar as a receptor, sugar on the cell surface. This is more like SARS-CoV-2 which also binds to a protein receptor. Measles viruses is genetically diverse, they're different genotypes and that makes it actually relatively easy to track outbreaks, investigate outbreaks and see where these viruses came from and how outbreaks are connected to each other. And that's important. We'll get to that later on when we talk about measles-free status that is granted by the WHO to countries. As I mentioned, this is a human virus, it really only circulates in humans, you can experimentally in fact non-human bremits or monkeys with the virus but typically it is only found in humans. And it's just transmitted via the air, either via aerosols, so these are these very, very tiny droplets that stick in the air for a very long time or by respiratory droplets, larger respiratory droplets that usually kind of fall to the ground quicker. These viruses are very infectious. We have previously discussed these are not a basic reproductive number which specifies how many people an infected person infects and for measles these are not 11 to 18. So a person infected with measles infects about 11 to 18 new susceptible people. Of course if people surrounding an infected person are vaccinated, they're protected and they won't get infected but still viruses very infectious and if they're non-protected, non-vaccinated people around, they will likely get infected. The virus is known for a long time in humans. It has likely a common ancestor with this RindoBest virus that I mentioned and the idea is that it jumped the common ancestor of measles in RindoBest virus jumped into humans or started to infect humans. Maybe around 400 BC to 580, that's the estimate and the idea is that this ancestral measles version already had similar symptoms to the days measles virus. And the disease was already described in ancient Persia by Muhammad Takaria Eradzi. It was a philosopher and physician and he could already differentiate between measles, box and chicken box just based on the symptoms and that was approximately 900 AD. And so the idea is that there was a complete separation from this common ancestor with RindoBest virus around 1100 to 1200 AD and from then on we can probably talk about problem measles in humans. The virus itself was isolated in 1954 by John Anders and Thomas Beables at Boston Children's Hospital from a 13 year old boy called David Edmondson and keep that name in mind. We'll get back to that later when we talk about vaccines. And John Anders was also involved in the discovery isolation and cultivation of polio virus and he got the Nobel Prize for that, I think also in the same year in 1954. So how do you get infected? I mentioned earlier that the virus is spread by aerosols and droplets. So basically the infection starts via inhalation and the lung is getting infected and from the lung the virus reaches local lymph nodes and there it starts to replicate quite rapidly. And after approximately seven days after the infection started we see first barinia. Barinia basically means that the virus is spreading through the blood and this is usually when first symptoms occur, these first symptoms are often respiratory symptoms, sniffles, calf, bronchitis, often also conjectivitis, so eye infection and then fever. Then around day 12 to 13 after the initial infection we see a second barinia and that triggers this typical rash that you see with measles. And this rash often starts behind the ears and then spreads throughout the body. This is often also associated with a second fever wave. And then four to five days after symptom onset, typically the infection starts to resolve if it's a mild case. So when are people infectious? About four days before the onset of the rash to four days after the rash is gone. And of course this is problematic because that means an infected person can already pass on the infection before it's clear that the infection is measles. Typically people understand that they have measles when the rash starts and they can spread the virus before that and that's of course good for the virus and helps the virus to spread because if you just have relatively unspecific symptoms you don't think about this and you spread the infection. Typically the disease is more severe in adults than in kids but of course most adults are actually immune because either they were infected in childhood or most of them were vaccinated. When we look at kids about two-thirds of the cases in kids are uncomplicated cases but about one-third of the cases come with complications. This could be a diabetes media, a diarrhea for example but in five percent of the cases we see pneumonia. So of course the virus replicates in the lungs so the lung is involved. But depending on where the case happens which country, which area, what the health status of the kid is, what the living standards are, if how the nutrition status is, the mortality rates can be relatively high. They're typically described as one to five hundred to one to a thousand from measles but there are studies that also see one to three hundred thirty fatality rate and immune suppressed individuals this can be much higher up to thirty percent. The situation is also different between high income countries and low and middle income countries depending on the outbreak and again on the setting the case fatality rates, the mortality rate in low income countries can be up to twenty-five percent. This actually also tracks with historical mortality rates in the US and Europe.
So, you know, back before healthcare improved, before nutrition improved, before hygiene improved and so on and so forth, the case fatality rates in Europe and in the US were pretty high too. That can be also rare side effects with measles. One of them can be meningitis and if that occurs, the case fatality rate is even in high income countries 10 to 20% and kids that survive that often have long term issues. And there's a rather difficult carry disease that's called subbecute clear rose in balance of alighties or SSPE that sounds bad and it actually is pretty bad. What happens here is that you have virus replication and inflammation in the brain that also leads to scarring of the brain. It's a very slow progressing disease and can be pretty deadly. So typically if kids under the age of 5 are getting infected with measles, 2 to 6 of 10,000 kids develop this SSPE when kids get infected under the age of 1 year, this rate can be up to 1 to 600 according to studying california. So what happens here is that kids get a regular measles infection and the virus stays in the brain and doesn't too much damage there, almost like its torment and this can last up to 10 years and then symptoms start. Typically seizures, paralysis, dementia, this moves very slowly but the problem is the case fatality rate for SSPE is about 95%. So unfortunately it's a very tragic situation. Typically the kid already had measles, survived it, was uncomplicated and then years later unfortunately the virus starts to become active again and causes this very severe disease. And it's interesting because similar cases are also described for other baromic viruses. For example one such case is described for handra virus in Australia. And also got infected with handra virus, survived the infection but then later the virus started to replicate again in the brain and the person type. Unfortunately there was also indirect issues with measles. Missles virus infects memory B and D cells so these are part of the adaptive immune system and they can also persist in these cells for up to 6 months and that affects immune memory, basically kills off immune memory and this immune amnesia can last over months. And what happens there is that if this memory B and D cells disappear or non-functional anymore, kids get very susceptible to other infections. Typically viruses or bacteria that would just cause mild infections usually but all of a sudden kids can have very severe infections with viruses like adenovirus which is relatively harmless for healthy kids and these infections can and fatal as well. There's actually a very good paper by Michael Mena and the up-oaster house and I'll provide a link to that paper so people can look it up but many people don't know about these indirect effects and that can be pretty problematic too. Just a little bit of trivia here, Raul Dahl, the writer, his daughter died of measles when she was 7 years old and I think that was before the vaccine was available and he later on really helped to promote measles vaccination to avoid such tragic cases. The interesting thing with measles is that people who survived measles infections which is the majority of infected individuals develop pretty strong immunity and that typically leads to herd immunity in a population. There have been studies that determined that for measles virus to kind of stay circulating in the population, stay alive in the population, it needs at least the population size of 250,000 to 500,000 individuals. That was determined when island populations or indigenous tribes were studied where the virus made it into that population and if that population was too small, the virus just burns through the population but then couldn't infect anybody anymore and basically disappeared. But if the population size was big enough then there were always kids that were born that were susceptible and so the virus basically stayed in the population. But that's also interesting and this point starts potential measles elimination if you have a good vaccine and very high coverage because of course measles doesn't circulate in animals. So once it's gone in the human population it would really be eliminated and eradicated. Unfortunately we were still pretty far away from that and actually we're moving in the wrong direction. So if you look historically and you go back to the year 2000 there was an estimated 800,000 measles deaths globally per year. And then there was a lot of work in terms of vaccination campaigns and that really reduced the number of cases globally and the deaths and as it estimate for 2022 is that there were about 100,000 measles deaths globally and about 10 million cases. You find these cases around the world, Africa is most affected by measles but basically you have outbreaks on all continents. Of course many countries have also eliminated measles circulation through rigorous vaccination campaigns and through high vaccination rates and when the country eliminates measles circulation it can get measles free status from the WHO. That doesn't mean that there are no measles cases at all in that country just means there's no constant circulation and you have to prove that so if a country has outbreaks and can be proven that these outbreaks are not connected and they are from introductions from outside from other countries then that's not a problem and you can do that through sequencing the virus and tracing it back. So that's why this diversity in genotypes is important because that makes it easy to trace the virus. But if it turns out that the virus is circulating constantly in a country then you lose that measles free status and Canada just lost these status in 2025. The US for example still has it. I don't know for how long but we'll see. And I mentioned that there's a lot of measles cases in Africa for example but we see measles come up quite a bit also in North America and in Europe. Just a few numbers for 2025 here. Mexico had around 6000 measles cases in 2025. Canada had 5,400 in 2025 and as I said lost the measles free status. The US had 2,200 cases, about 2,200 cases in 2025 with three deaths and about 11% of the infected individuals had to be hospitalized according to the CDC. So that's highly problematic. So we also see a lot of cases in Europe. Romania for example had about 8,000 cases last year. Germany had 250, France had 800. So there's an increase in many Western countries including North America and Europe and that of course has to do with basically lower vaccination rates. And if you have gaps in vaccination then there will be increases in measles and measles will start to circulate again. As I mentioned measles can be prevented by vaccination and there's a very well established, a very effective and very safe vaccine. And this vaccine was developed based on the virus that John Anderson isolated in 1954 from this kid at Monster. And so the vaccine strain is also called after that kid it's called at Monster strain. What happened back then was that John Anderson's passage to the virus which just means he cultivated it over and over again in the laboratory, first in human cells and then in chicken cells. And so what happens when you do that with the virus when you switch species in terms of the cells it's growing on then initially typically the virus doesn't grow well on these new cells initially. So measles is a human virus it's not equipped for growing on chicken cells right. And if you do that over and over and you passage the virus on in chicken cells then it starts to mutate and it optimizes its growth on chicken cells. And what often happens in that process of adaptation to a new cell to a new species is that the virus loses the ability to efficiently grow to efficiently replicate in human cells. And that weakens it in the human cells and in humans we call that attenuation. And that's how chiasically this life attenuated vaccines were made. And so this was also the case for measles it's a very chiasical way of making vaccine strains of attenuating and weakening them. And the strain that was developed was called at Monster B strain. There was used this vaccine but it wasn't attenuated enough and so in 1968 new strain was developed and introduced that was even weaker. [BLANK_AUDIO]
further denuated and that was done by Maurice Hilleman. Maurice Hilleman was a real pioneer in terms of vaccine development. He developed many of the vaccines that we are using nowadays and he had a really interesting life and there's a really good book about him and I'll leave a link to that book in the comment section. From that strain that Hilleman developed basically three strains were derived. The Edmondson Saga abstraint, the Marathon strain and the Swords strain and those are basically vaccine strains that are still used nowadays. In 1971 this measles vaccine was combined with the Mums and Rubella vaccines which are also life-ed-envaded, weakened vaccines and that became known as the MMR vaccine. So measles mums, Rubella. And this vaccine was super effective and in the US for example is led to a drastic reduction of measles cases. It had a efficacy of about 93% against measles but because measles is so infectious it still caused cases at a very low level in the US even after that vaccination started and so the idea was to give a second dose of the vaccine. Initially only one dose was given and if you give a second dose you get an efficacy of 97% and that was really enough to stop measles variculation in the United States. And so the estimates are that this vaccine prevented about 57 million measles deaths between the year 2000 and the year 2022 so that's a huge number of lives saved. Luckily this vaccine is given at 12 months of age before that typically babies are protected by antibodies that they got from their mothers through the placenta because these maternal antibodies. And so if you give the vaccine earlier than 12 months often it doesn't work well because of course this antibody is from the mother also key love to vaccine strain and then doesn't replicate and then you don't get a good immune response. So typically it's only given at 12 months of age and then the second dose is often given between 15 and 18 months of age. The recommendations differ a little bit between countries but that's kind of general in general the schedule. The vaccine because it's a life virus vaccine can have side effects it can cause fever or a mild rash but this side effects are actually relatively rare and it's super safe vaccine. However because it's a life virus it cannot be used in people who have issues with their immune system cannot be used in pregnant women for example who have a down regulated or in some aspects down regulated immune system can also not use it in immune compromised individuals and people with underrated HIV because in these cases it could replicate better and do some damage even though it's a weak infoxine. But again it's a very successful vaccine saved many many lives. We have a problem with this vaccine and this has to do more with perception and with the vaccine itself and that goes back to 1998. In 1998 British doctor Andrew Wakefield published a paper in the Lancet. So the Lancet is actually a pretty good medical journal but sometimes even they make mistakes and so this Andrew Wakefield published a study that he had done on 12 kids that had what he described as autistic and aracholitis. So basically intestinal inflammation plus autism and he said that there are hints that this is connected with the MMR vaccine. Actually going through that baby and what followed and the investigation that followed and so on and so forth were in its own episode I'll keep this brief today to keep it short. Basically the study was nonsense in a scientific sense and 2004 it was partially retracted so taking back basically and 2010 it was completely retracted. There were relatively intense investigations or what happened there and it turned out that this Andrew Wakefield had massive conflicts of interest. He was paid to do that study but he didn't disclose that. I think there was also a lack of ethical approach to do the study which is not good and in the end he lost his medical license in the UK. So basically it didn't make any sense and the data wasn't really supporting what the claim was but of course there were a lot of reports in the media and that fueled skepticism about the MMR vaccine and fears of parents that the vaccine would cause autism if they get their kids vaccinated and that impacted quite a bit on vaccination rates. Vaccination rates went down because of that and that is one of the reasons why we have this current increase of measles cases specifically in Western countries. Of course initially this was taking very serious right so if you see a study like that and there might be an association you have to look into that. It might be true right? So it's important to investigate that and there were actually a large number of follow-up studies, quite big follow-up studies, quite expensive follow-up studies. One example is a 2012 core crane study that included analysis of about 14.5 million kids and they didn't find any association between MMR and autism. One of the studies that were done subsequently found an association between MMR and autism. In a way doing this study is great because it proves again that the vaccine is safe and there is no issue. But you end up with one study with 12 kids with massive conflict of interest involved on one side and a large number of studies with millions of kids and good study designs on the other side and people still believe what Andrew Wakefield published back then and don't vaccinate their kids. So the problem is really that once fake information is out and once conspiracy theories are out it's really hard to counter them even if you have hard data that says it's not the case right? People just start to believe these things and it's really hard to get this out of their minds. In summary the situation with measles is a problematic disease with rising case numbers mostly fueled by vaccine skepticism and false information. It's a big problem and it will be an even bigger problem in the coming years and this is actually sad because this is a virus that is restricted to humans. We have a very good vaccine and that means we could eradicate it. We could get rid of it in the human population but unfortunately we are going in the completely wrong direction right now. So this is the end of today's episode. As always if you have comments, suggestions or questions please write an email to
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