Vaccines are the literal embodiment of the maxim ‘prevention is better than cure’. When it comes to healthcare it’s far better to stop something happening in the first place than it is to repair the damage after it has happened. Thankfully that’s what a vaccine does, it grants you immunity (effectively) to a disease. This is fortunate because many of the diseases that we can vaccinate against leave pretty significant damage.
How vaccines work
A vaccine relies on the incredible ability of your immune system to remember a disease from last time and mount a quicker and more effective response the second time. This is what I mean by effective immunity because even though you received the vaccine, the disease causing bacteria or virus may still get into your body. But because your immune system is prepared for it the response is so fast and effective that you don’t even notice.
As an aside, your immune system’s memory can be a bit of a double edged sword because it’s also the cause of allergic reactions. An allergic reaction happens when your immune system decides that something quite harmless is actually a real threat. One of the most common allergic reactions is hay fever where the immune system mistakenly believes that pollen is dangerous and mounts an immune response to it. The faulty immune response to pollen is to try to force it back out of the body and keep it out which as any sufferer knows involves runny eyes, noses, sneezing and the rest of it – your body is simply trying to minimise the amount of pollen that can get in. It sucks, but thanks to your immune systems memory it will happen every time you encounter pollen for the rest of your life.
You should be thankful though if hay fever is the worst of it. Some more serious allergic reactions, such as one to penicillin or insect stings, can cause anaphylactic shock where the immune response may include swelling of the throat which prevents breathing or widening of blood vessels which causes a potentially fatal drop in blood pressure. The first time you suffer an allergic reaction will be reasonably mild and probably not life threatening but this is like your warning from the universe because, thanks to your immune system memory, the next time you have an allergic reaction it will be faster, stronger and potentially fatal.
The first ‘vaccine’
So how did we figure out vaccination? Well, unlike antibiotics, it was actually quite a long time ago.
Arguably the first vaccination was used in China in the 15th Century against one of the most deadly diseases of the time; smallpox. It was already clear that someone who got smallpox and didn’t die never got smallpox again which suggested to them that recovery from the disease granted immunity to it. This information was useless though if you wanted to prevent the disease in the first place but what if it could be weakened first?
It was discovered that taking the scabs from someone with smallpox, leaving them out for some time to dry and then snorting them through the nose would produce a smallpox infection notably less severe than the natural infection but granting full immunity afterwards. Absolutely disgusting, but better than smallpox.
This form of vaccination was called variolation (variola being the Latin name for smallpox) and despite causing a few deaths itself, it was still safer than naturally getting smallpox. Variolation finally made its way to Britain in 1721 and became the de facto vaccine for smallpox in Europe.
The first real vaccine
Continuing with smallpox, as it was still very much one of the most prevalent and deadly diseases of the time, in the late 18th Century a scientist called Edward Jenner noticed that people who became infected with cowpox seemed immune to smallpox.
The story goes that he noticed that milkmaids always had beautifully smooth skin as a result of never contracting smallpox (which would leave pock marks or scars on the skin of survivors). This, he attributed to them working with cows who were known to suffer from the far less deadly cowpox. Cowpox could be passed to humans, seemingly granting an immunity to smallpox. The beautiful milkmaid part of the story is debated nowadays but it is a rather more romantic way of describing how Jenner noticed the protective capability of cowpox.
This led him to perform one of the most ethically questionable experiments (by today’s standards) to prove his theory. He took pus from the sore of a milkmaid suffering from cowpox and inoculated an 8 year old boy, the son of his gardener, by applying the pus directly into small cuts made onto both arms. After about a month the boy was infected with smallpox using the variolation method and miraculously developed no symptoms of the disease. Several months later the boy was infected again with the variolation method and again developed no symptoms of the disease, leading Jenner to confirm that overcoming cowpox infection granted immunity to smallpox infection.
Despite initial caution by the medical establishment, Jenner’s arm-to-arm smallpox vaccine was finally accepted and variolation was halted in 1840 in favour of Jenner’s vaccine. News of the vaccine soon spread around Europe and eventually to the rest of the world.
Following a global effort led by the World Health Organisation (WHO) using a smallpox vaccine that didn’t require cowpox pus, smallpox has been officially eradicated since 1979. The disease exists now only in secure laboratories for research purposes.
Types of vaccine
We’ve come a long way since rubbing pus into wounds as a form of vaccination and we now have many methods that we can use. But by far the most common methods are the use of inactivated vaccine and a live attenuated vaccine.
Inactivated vaccine is pretty self explanatory, the disease causing bacteria or virus is killed or made inactive by heat, chemicals or radiation. The inactivated bacteria or virus is then given to the patient, usually in the form of an injection, and the body’s immune system treats it as the real thing. This causes the body’s immune system to develop a memory of the disease so it can effectively fight it next time.
One issue with this vaccine is that the bacteria or virus is dead so it can’t replicate in the body, that sounds like a good thing but hear me out. Without replication the immune system can ‘forget’ the disease so these vaccines are usually followed up with boosters or booster shots. This keeps the bacteria or virus in the body long enough for the immune system to properly generate memory.
Examples of vaccines that use this method are effective against influenza (the flu), cholera, bubonic plague, polio, hepatitis A and rabies.
A live attenuated vaccine is slightly more complicated. The disease causing bacteria or virus is made less virulent or less effective, in most cases harmless, but it is still live. That means it can still infect you and replicate inside of you but its ability to cause disease is removed. This has a distinct advantage over inactivated vaccine because it continues to replicate inside the body (albeit at a much slower rate than normal) so boosters are not so often needed. No one likes getting an injection after all and this also saves a lot of time for healthcare professionals.
However, there is, in some live attenuated vaccines, a tiny, tiny chance that the disease causing bacteria or virus will mutate and restore it’s natural virulence. We’re talking a millions to one chance of course but that really sucks for that one guy. Furthermore, live attenuated vaccines can’t be used by people who are immunocompromised such as HIV sufferers because their body has no defence even against this weakened bacteria or virus.
Unfortunately, there are some bacteria or viruses that can’t be vaccinated against using inactivated vaccine and they need to be live attenuated. Healthcare professionals take this into account when developing vaccines and certain safeguards and ethical considerations need to be met before the vaccine will even hit the shelves. Is it worth it to immunise 1 million people against a disease if one person will get infected? Keep in mind that the disease is still unlikely to be fatal. And we must remember that when the entire planet has the vaccine and the disease is thereby eradicated, then, like smallpox, we won’t need the vaccine anymore. In the case of smallpox for example, the vaccine was fatal for 1-2 people per million vaccinated. We have to consider whether that is worth it.
Examples of other live attenuated vaccines are tuberculosis (BCG vaccine), measles, mumps and rubella (MMR vaccine), influenza, chicken pox, polio and typhoid.
Case study: Polio
You may have noticed that polio has both an inactivated vaccine and a live attenuated vaccine. The reason for this is super interesting and highlights one of the things that healthcare professionals need to consider when preparing and prescribing a vaccine.
Polio is primarily a disease of the intestine and is passed on through the fecal-oral route. That means the only way you can get it is if you eat/drink something that contained the feces of an infected person. Therefore, it’s pretty hard to catch it but if you do catch it there’s absolutely no cure. You will have it for life.
The good news is that 72% of people who have it will show no symptoms so effectively you might as well not have it. 24% of people will have minor symptoms like a sore throat, nausea and flu like symptoms and 1-5% of people will have major symptoms similar to those of meningitis. But about 0.1-1% of people, 1 in 1000 children or 1 in 75 adults, will develop permanent paralysis. That’s not confined to limb paralysis, in some cases it can cause paralysis of the muscles used for breathing which is immediately fatal.
It’s horrible, but that doesn’t mean it’s not interesting. You see, although the virus starts in the intestine, it can move into the blood stream and from there into the central nervous system. This is what happens in those who develop paralysis. And this is a significant problem for doctors because although I’ve been describing immunity as a binary thing – you either have it or you don’t – it’s actually a bit more complex than that…
The polio vaccine
The immune system has both cell-mediated immunity, such as that which is present in the intestine where polio starts, and humoral immunity which blocks the polio virus from entering the blood and central nervous system. What’s interesting is that the inactivated polio vaccine, which is injected into your bloodstream through your arm, gives you immunity to the virus travelling in your blood – effectively making you immune to paralysis should you get infected by polio. But it does nothing to stop polio from infecting your intestine in the first place. The live attenuated polio vaccine however does get into your intestine, replicates there and travels in your blood just like the real virus so you get immunity to both the initial infection and paralysis.
So maybe you’re thinking, why do we even have the inactivated vaccine if the live attenuated vaccine is better? Well, the live attenuated vaccine, like many other live attenuated vaccines, has a chance to mutate and become fully virulent again. Because of this, one person per million vaccinated will get paralysed from the vaccination. Now, this is where healthcare professionals need to think carefully about who to vaccinate and it all comes down to statistics.
We need to ask ourselves if one paralysis per million is a big number or a small number based on the number of polio infections in that country. For example, in countries like Pakistan or Afghanistan where polio is a legitimate concern it’s better to risk one paralysis per million to stop the spread of the infection at the source. But in a country like the US where the chance of even getting polio is less than one in a million, there’s no sense using a vaccination that will paralyse more people than get infected in the first place.
The situation was different 20 years ago. Almost every country used the live attenuated vaccine because getting polio was a legitimate concern everywhere. The success of the vaccination means that more and more people now only take the inactivated vaccine and eventually, like smallpox, no vaccine will be necessary.
Case study: Influenza
You may have also noticed that influenza has an inactivated vaccine and a live attenuated vaccine. We’ll come back to that in a minute but firstly we need to talk about the influenza vaccine because it’s also pretty interesting stuff.
The thing about influenza is that it’s not just one virus. There are lots of slightly different influenza viruses that all cause the same disease but all look different to your immune system. To give you an idea of how many there are think about the last big flu scare – the H1N1 swine flu of 2009. That sequence of numbers and letters tells us about the type of flu we’re dealing with where the H and the N are two proteins called hemagglutinin and the neuraminidase, respectively. Of these proteins there are 18 different H and 11 different N giving us the possibility of any flu from H1N1 through to H18N11 and every combination in between. There are also different strains within these numbers. For example, the 2009 H1N1 swine flu was a different strain to the previously identified H1N1 and has now since replaced it as the dominant strain. Now I’m going to tell you that this is only type A influenza, there are also types B and C which also include their own further strains.
Incidentally, this is the same reason we can’t cure the common cold, there are so many different types of influenza virus and so many types of cold virus that are constantly changing and evolving that we simply can’t vaccinate against them all. So how do we make a flu vaccine?
The influenza vaccine
As you might already know, the flu vaccine changes every year and it’s recommended that you get a new flu shot every year to protect you from whatever the dominant flu type is. The interesting thing is that the vaccine protects you against the flu virus type that research indicates will be the most common in the upcoming season.
The truth is that it’s impossible to know for sure which flu types will predominate in the coming year. Hell, the dominant type can even change within the same season. To further complicate matters, scientists need to say which flu they believe will predominate many months before the flu season even starts in order to prepare and produce the required amount of vaccine for everyone to get vaccinated on time.
That doesn’t mean that getting a flu vaccine is ever a bad choice, particularly for those groups at high risk – the young, the weak and the elderly. We’ve been doing this a long time now and we are very good at predicting which flu type will predominate. This isn’t guesswork, data are published weekly on which flu types are circulating per season with further data being published after the season about the overall effectiveness of the vaccine and suggested improvements.
In addition, the flu vaccine is designed to protect against three or four different flu types to ensure that we are covering all bases and even if the vaccine isn’t exactly right it can still provide lowered protection against a related type. For this reason, the vaccine is sometimes inactivated and sometimes live attenuated depending on the predominant flu type. Often, both types are offered with no real disadvantage to either one but the more we have the more people we can vaccinate.
Sometimes, like in the case of the 2009 swine flu, the predominant flu type is completely resistant to the vaccine and therefore poses a significant threat to those high risk groups. This is when a new vaccine needs to be immediately prepared. This takes time, time the virus can use to become an epidemic which is always a possibility. The 1918 H1N1 Spanish flu killed more people than the amount of soldiers that died in the First World War (1914-18), killing some 3-5% of the worlds population. We like to think that we are better prepared 100 years on but if our vaccination doesn’t work that year we are in no better position than those in 1918.
We can tend to trivialise the flu as ‘just a bad cold’ but the flu is a legitimately dangerous disease that can even be fatal in the young and strong and we should not underestimate it.
Disease eradication through vaccination
Does the MMR vaccine cause autism?
No. It doesn’t.
The scientist, Andrew Wakefield, who wrote the original paper claiming a link between the MMR vaccine and autism has been shown to have falsified his data. As a result the paper was retracted from the journal and he was stripped of his medical license. No follow up study has ever been able to reproduce his results and the most recent study of 95,000 children has shown no evidence of a link between vaccines and autism even among children with autistic siblings.
periodicallyamended 
As of now smallpox is the only disease to be eradicated entirely due to vaccination but many diseases are well on the way.
Polio is almost completely eradicated with only 56 cases so far in 2015, it’s already considered eradicated in the Americas and Europe.
Measles, mumps and rubella (German measles) are also almost completely eradicated in the Americas and Europe with just a handful of cases each in 2015. However, these diseases have actually been rising again over the last couple of years and that is all thanks to the belief that the MMR vaccine causes autism…