thanks to brilliant for supporting this episode of scishow good a brilliant daughter slash scishow to learn more about their statistics fundamentals course this episode was filmed on April 22nd if we have a more recent episode about reinfection we will include it in the description there are now dozens
of potential vaccines in development to fight the Cova 19 pandemic some of which are already being tested in humans vaccines are one of the most powerful tools in medicine because they offer a path to immunity without having to get seriously sick and once enough people have immunity either
because they got vaccinated or because they survived the disease we can achieve herd immunity and dramatically slow the infection rate except all of this only works if it's actually possible to build up long-term resistance to SAR CoV – to the virus that causes kovat 19:00 and that unfortunately
is not a sure thing so today let's look at how immunity works how the corona virus could sidestep it and why thankfully it's too soon for us to be worried immune system is basically our body's defense against infections and like any good defense it has a number of
layers these broad terms you can break the immune system into two chunks the innate and the adaptive the innate immune system provides our generic defenses that are always in action these can be like physical barriers like your skin or the tiny hairs inside your nose both of which
help keep pathogens from entering your body at all but the innate system also provides special kinds of cells that circulate through the body and attack anything that seems out of place for example macrophages surround and basically consume hostile cells while releasing chemicals that activate other parts of the
immune system there are also the amazingly named natural killer cells which quickly attack viral infections to buy time for other more specific helpers to arrive those helpers come from the adaptive immune system which tailors itself to the specific attacker the body is facing the adaptive system uses things
like b-cells which quickly reproduce and create antibodies designed to overwhelm and destroy some specific pathogen it also uses t-cell which can help regulate everything or even attack viruses themselves when your body sees a new intruder like SARS CoV – it takes time for these specialized cells to develop
and reproduce once you get better most of them die but a few called memory cells can stick around they hang out in places like your lymph nodes and spleen and if they see their old enemy again they can quickly produce the cells needed to destroy it when this
happens someone is said to have active immunity and it's what scientists are generally talking about when they talk about lasting immunity – kovat 19 in some cases like for chickenpox immunity can last a lifetime but for other infections like whooping cough that protection can last only a few
years after that the body decides for some reason or another that it doesn't need those memory cells anymore so the big question facing researchers right now is where on that spectrum the novel coronavirus falls right now there is at least a little evidence that it's possible to get
sick with kovat 19 a second time for instance the South Korean CDC has reported at least a hundred and eighty cases of apparent reinfection which is about two percent of everyone who's recovered and about half of those people have mild symptoms again although there's no evidence that they
go back to being contagious there are a few reasons why patients might test positive after having seemingly recovered one could be that the test South Korea is using just isn't that accurate but that's not very likely to be declared recovered patients have to have two consecutive negative tests
spaced out by at least a day it is possible that the test is giving misleading results though that it's correctly picking up bits of SARS CoV twos genetic material but that those bits were just the destroyed remains of the virus there's even a little evidence to suggest that
because of that some experts aren't concerned about reinfection x' but others are keeping an eye on it because testing aside there are two big biological explanations for why a recovered patient might get sick again the first is called a latency and it's the idea that a virus can
hide out in the body only to re-emerge later a common example of viral latency is herpes around ninety percent of people worldwide are infected with the type on herpes simplex virus which can cause cold sores to develop most of us don't have cold sores all the time because
the adaptive immune system can effectively remove the virus once it's detected but because of latency herpes stays with us our entire lives by embedding itself inside sensory neurons within the brain since our immune system knows not to just blithely destroy brain cells which you know is pretty nice
of it herpes can hang out there long term as long as it stays relatively quiet then under various circumstances like if you're stressed out the virus can reactivate and a new round of cold sores forms latency though isn't typically seen in other human coronaviruses like the ones that
cause the common cold so unless we find evidence that suggests otherwise there isn't a huge reason to believe this is true of the novel coronavirus the other big possibility is that SARS CoV – just might not elicit a long-term immune response if your immune system doesn't create many
memory cells or if they don't last very long then it would be possible to catch kovat 19 get better and then catch it all over again like it was new that seems to be the case with the corona viruses that cause the common cold like in one study
of recruits for the US Marine Corps in the early 1970s less than a half of those who caught a certain strain of cold produced enough antibodies to fend off a reinfection why this happens is still more or less a mystery in part because colds are so mild that
researchers in the 20th century didn't put much effort into studying corona viruses and unless there's been a major outbreak researchers today don't tend to focus on them much either but some scientists think that memory b-cells are created with specific lifetimes and that viruses that cause a bigger immune
response result in longer lived memory cells since corona viruses can suppress the immune system's response that might lead to shorter periods of immunity fortunately not all corona viruses create immunity as ineffectively as the common cold the virus causing kovat 19 seems to share much of its structure with
the one that caused SARS back in the early 2000s and that infection did result in longer term immunity for most people in a 2007 study of 176 people who survived their SARS infection protective levels of antibodies lasted for on average around two years in a study of three
patients published in 2016 found the presence of memory t-cells 11 years after their recovery from SARS of course just because the SARS virus is similar to the one that causes kovat 19 doesn't mean immunity has to work the same way in both diseases looking at SARS is one
way we can form a hypothesis about Kovan 19 but in the end there aren't really any shortcuts to figuring out our lasting immunity to this virus if the answer is ultimately what we want to hear like say if infected or vaccinated people develop immunity for a decade or
more we won't really know that for a decade or more but if the answer isn't as encouraging like if immunity lasts for only weeks or months we'll start finding that out much sooner no matter what the answer is though it will be an important one because it will
guide where scientists focus their efforts and resources like if this virus has a very short period of immunity all hope won't be lost that would just mean it could be more important to find effective treatments rather than a vaccine which researchers are also working on already and actually
we just did a whole episode about some of our best bets which you could watch right after this ultimately because of all this it's too early to really worry about kovat 19 re-infections and no matter what future studies say there will still be things all of us can
do to keep ourselves and each other safe after all wearing masks and keeping our distance will help reduce transmission regardless of whether someone has been sick before or not in the meantime doctors and scientists are working quickly to learn key details about the new corona virus and once
they've got them they can help the world make decisions about what we should do next if you want to learn more about how people study pandemics learning about statistics is a very good first step and if that sounds right up your alley you might enjoy brilliant statistics fundamentals
course one of its goals is to help you pull truth out of a data set and it's got lots of quizzes and interactive modules to help you get there brilliant also has plenty of other courses about science engineering computer science and math so whatever you're into you've got
options if you want to check it out the first 200 people to sign up at brilliant org slash scishow will get 20% off their annual premium subscriptions you [Music]
