in this video we're going to take a look at how vaccines work and consider their pros and their cons once our bodies or more specifically our immune systems have been exposed to a certain pathogen they generally develop immunity to that pathogen and any of the diseases it causes and once we're immune it means that we can't catch the disease anymore which is why only catch things like chickenpox once the problem though is we still have to catch the disease that first time which can range from being unpleasant to lethal what would be great is if we could somehow expose oursel to the pathogen and get the immunity without actually catching the disease well this is exactly what vaccines do inside a vaccine are the pathogens that we want to be immune to but importantly they've been weakened or inactivated so that they aren't strong enough to cause us any disease because these weakened pathogens still contain the same antigens though our body still treats them as if they're the proper pathogens and so it responds by producing antibodies and developing immunity we now have vaccines for so many things that it's easy to forget just how many diseases there are out there vaccines can work against both bacteria and viruses and by the time we start primary school we've already been vaccinated against more than a dozen diseases many of which could otherwise kill us so what are the pros and cons well the main Pro is that they protect us from Catching horrible diseases but on a larger scale they've actually helped us control loads of diseases that used to be quite common like polio small box measles and hooping cough they also help to prevent big outbreaks of disease which you call epidemics these waves of disease used to spread rapidly across the country and kill a big portion of the population vaccines are able to have these large scale effects because of something called herd immunity when enough people in your population are immune to a pathogen then the pathogen won't have any people to spread to so once the host overcomes the disease or dies then the pathogen disappears so even if a few people aren't vaccinated they're unlikely to catch the disease because everybody around them is vaccinated now the pros pretty much always outweigh the cons when it comes to vaccination but there are a couple of problems for one vaccines don't always work sometimes they just don't grant us full immunity but with important vaccines we generally check after we've had the injection to see if it's been effective a more common problem is that we sometimes have bad reactions to the vaccine for example some swelling around the injection site in some severe cases they can cause fevers or even seizures however bad reactions are pretty rare and the severe reactions are super rare if you haven't heard yet you can find all of our videos on our website Cognito dog you'll also find questions flashcards exam style questions and past papers and we track all of your progress so that you always know what to study next so sign up for free by clicking here or browse our playlist here on YouTube