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  • Thanks to KiwiCo for supporting this episode  of SciShow! Head to kiwico.com/scishow50  

  • or click the link in the description to  get 50% off your first month of any crate.

  • [♪ INTRO]

  • So you show up for your annual physical and the  doctor tells you you need a ten-year booster shot.

  • But you've already had all  your routine vaccinations,  

  • so what's in that syringe that's so important?

  • Well, the vaccines we have all dopretty good job of introducing our  

  • bodies to certain diseases and convincing our  immune systems to take that threat seriously.

  • But for some diseases, it takes  extra convincing. Which is why  

  • you might need to get the same shot more  than once -- weeks or even years later.

  • Vaccines teach our immune systems to recognize  certain pathogens, or disease-causing agents.

  • In a nutshell, they trigger the formation  of specialized cells and antibodies that  

  • recognize the distinctive proteins that  stick out of pathogens -- called antigens.

  • If something with one of those antigens shows  its face, the antibodies latch on and disable it,  

  • while those specialized cells  help to kick it to the curb.

  • Now, there are a few vaccines that  require multiple doses of the same  

  • shot. And there are almost as many reasons  for that as there are different vaccines.

  • Because how much immunity you get from a single  shot, and how long it lasts, can really vary.

  • Some vaccines, like the Hepatitis  A vaccine, tend to require  

  • multiple doses to dial immunity up to the best  possible levels when you first get them.

  • Others, like the shot that  protects against tetanus,  

  • require getting the same shot years  later to dial immunity back up to full  

  • throttle -- what we often call a booster  shot, though the terminology can vary.

  • And scientists are learning that  some vaccines, like the HPV vaccines,  

  • may provide solid immunity for  more than a decade with just  

  • one shot -- even though their efficacy  was first established using multiple doses.

  • Like I said, immunity can really vary

  • Immunology is notoriously complicated, and  we're still trying to understand the details  

  • of how our existing vaccines  work on a molecular level.

  • So, we're still working out the right  number of shots and when to give them.  

  • In some cases, that even applies to diseases  we've been vaccinating against for decades.

  • But in general, you might need to go  back for a top-up because immunity  

  • doesn't always last forever.

  • Basically, over time, immunity to some  threats can get sluggish as immune memories  

  • get fuzzy and the numbers of  specialized cells dwindle.

  • It seems to happen in tiny  sites called germinal centers.  

  • These form in the lymph nodes and  spleen upon encountering a new antigen.

  • These centers are where immune cells  hang out, maintain their numbers,  

  • keep their memories sharp, and lie in wait  in case their pathogen-of-interest shows up.

  • Those cells include the B cells that  make antibodies, as well as T cells,  

  • which are also thought to  help remember past invaders.

  • When germinal centers form, specialized  cells grab copies of the antigen  

  • and B cells get to work testing out antibodieskeeping only the ones with the tightest grip.

  • How well immunity builds up in the first placeand the extent to which it wanes over time,  

  • might depend largely on how  efficiently this process goes down.

  • Immunologists are also still figuring out how  time and the elements take a toll on how well  

  • older people's immune systems work to fight off  pathogens that they've been vaccinated against.

  • Researchers are still working on how to  tweak different vaccines to induce the  

  • formation of the best germinal centers to  get immunity to last as long as possible.

  • That said, we're still  learning how this all works!

  • Overall, though, whether we'll need booster  shots down the line depends on a few things,  

  • like how much our immunity declines.  

  • For example, people who contract measles  once are considered immune for life.  

  • And so are those who receive a pair of shots  of the vaccine we've been giving since 1967.

  • Many people -- though not all -- will develop  a robust immune response after just one shot.

  • The second dose just ensures that more  people will be thoroughly protected.

  • Measles surface proteins aren't good at mutating,  

  • so the antibodies you make will  keep recognizing them indefinitely.

  • But with other vaccines, our immune  system needs a lot more help.

  • Like pertussis, better known as whooping cough.

  • In the 1980s, many countries started  switching to a new version of this vaccine  

  • that only contained pieces of the  pathogen, instead of the full thing.

  • That was because the older  vaccine that contained killed,  

  • whole cells of the pathogen had  occasional nasty side effects.

  • The problem is, researchers  have realized more recently  

  • that immunity from this cell-free  vaccine wanes after just two years.

  • The current vaccination schedule calls  for kids to get their first shot a few  

  • months after their first birthday, and  the second one after they turn four.

  • So it looks like our vaccination  schedules will need to be updated  

  • to keep people protected from pertussis outbreaks.

  • Now, what about the vaccines on  everyone's mind -- the ones for COVID-19?

  • Many of these vaccines are administered in  a two-shot series, so the question is what,  

  • if anything, we'll need after that.

  • And right now, we're just not sureBut scientists are working on it.

  • One manufacturer, Moderna, plans to begin testing  booster doses of their current mRNA vaccine in  

  • July 2021, a year after the first clinical  trial participants received their shots.

  • Because it might be that we need boosters to rev  up waning immunity over time, like with tetanus.

  • To cover the bases, Moderna is also working  on a novel booster candidate against  

  • new strains that have emerged since  the initial vaccine was developed,  

  • just to be sure our immune  systems also recognize those.

  • But it's also possible that the virus might  continue to mutate in ways that make current  

  • vaccines less effective, requiring  a system more like the flu shot.  

  • Yearly flu shots aren't so much  boosters as whole new vaccines.

  • In short, we're going to need a lot more  information before we know exactly how often we're  

  • going to need to be vaccinated against COVID-19 --  and how much those vaccines will need to change.

  • The good news is, scientists are on the  case, so we won't be left hanging forever.

  • Like I said earlier, immunology is complicated. But we're getting better  

  • against COVID-19 -- and all the other pathogens that cross our path.

  • Thanks to KiwiCo for supporting  this episode of SciShow.

  • KiwiCo creates incredible hands-on  projects for kids.

  • I have a four-year-old, he's a lot of fun,

  • and having something that arrives every month that he and I can do together

  • to learn a little bit and have some like, hands-on, father-son activity time

  • it's a great excuse to hang out and do something together.

  • When you sign up for a KiwiCo subscription, each  month, a kid in your life will get a fun,  

  • engaging new project to help them  develop their creativity and confidence.

  • KiwiCo has eight different subscription  lines for different age groups  

  • and different topics, and all of them come with  everything you need for the project.

  • So you don't have to worry about - oh my god, I didn't- I left that thing in that place-

  • or I have to go back to the store- It's all there!

  • And you can pack it up and take it with you to your friend's house, or your parent's house.

  • Sometimes I save a couple up if I know that we're going to be going somewhere together.

  • They're colorful, they're fun, and they encourage  hands-on learning and curiosity.

  • If you want to learn morego to kiwico.com/scishow50,  

  • or click the link in the description. You'll  get 50% off your first month of any crate.

  • [♪ OUTRO]

Thanks to KiwiCo for supporting this episode  of SciShow! Head to kiwico.com/scishow50  

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B2 中高級 美國腔

为什么只有一些疫苗需要加强注射(Why Only Some Vaccines Need Booster Shots)

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    joey joey 發佈於 2021 年 06 月 04 日
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