Placeholder Image

字幕表 動画を再生する

  • Vaccines are medicines that train the body  to defend itself against future disease.

  • Unlike other drugs, which we give to some people  when they're sick, we give vaccines to huge  

  • numbers of people while they're well. That's one  reason vaccines go through such extensive testing.

  • Vaccines work by simulating an infection in the  body. This isn't a real infection, but it teaches  

  • the immune system to recognize and neutralize  similar pathogens later. If the immune system  

  • can stop viruses from replicating, they no longer  pose a health risk to the vaccinated individual.

  • We've used this strategy to develop  dozens of vaccines over hundreds of years.

  • People have been immunizing themselves for  centuries, starting in India and China.  

  • By the early 1600s, people were deliberately  infecting children with tiny doses of smallpox,  

  • in a process calledvariolation.”  Variolation was fatal about 2-3% of the time.  

  • But it made children immune to the diseasewhich was normally deadly about 30% of the time.

  • In 1717, Lady Mary Montagu, wife of  the British ambassador to Turkey,  

  • introduced the technique to the British  medical establishment. She learned about  

  • variolation from Ottoman practitioners, and  then used it to immunize her own children.

  • Decades later, physician Edward  Jenner learned that British dairy  

  • workers had discovered an even safer  protective option against smallpox:  

  • injecting people with cowpox, a  related but less lethal disease  

  • that turned out to confer immunity. Jenner  tested the theory by injecting an eight-year-old  

  • boy with scrapings from a milkmaid's  cowpox blisters. Fortunately, it worked.

  • When the immune system detects a virus, it  makes antibodies to neutralize it. The goal  

  • is to block the virus from binding to  healthy cells, so it can't replicate.

  • Because pox viruses are relatedand use similar binding proteins,  

  • cowpox antibodies also ended up  protecting the patients from smallpox.  

  • And it was much safer to inject  patients with cowpox than smallpox.

  • We no longer immunize people by  giving them diseases. Instead,  

  • we use vaccines, which work  similarly but are much safer.

  • In the 1930s, researchers discovered  they could inactivate seasonal flu  

  • viruses using a formaldehyde solutionFormaldehyde itself is toxic. But people  

  • injected with the inactivated virus particles  ended up developing protection from the flu.

  • To make a flu vaccine for the wider populationresearchers just needed a controlled way  

  • to generate lots of virus particlesinactivate them, and then harvest them.

  • Based on some early experiments, researchers  turned to fertilized chicken eggs,  

  • where the viruses multiply exceptionally fast.

  • [If we want to license it, Getty has footage  of eggs being injected in 1965 and 2000]

  • The first flu vaccines were released in the  1940s. Even with recent advances in cell culture  

  • technology, about 80% of flu vaccines are still  made using chicken eggshundreds of millions of  

  • them, sourced from farms that governments  keep secret to protect against tampering.

  • We can also make vaccines using live virusesweakened enough so they can't actually cause  

  • the disease. Alternatively, we can use  non-infectious pieces of the viruses,  

  • or particles manufactured  to resemble the pathogens.

  • Scientists' latest strategy to fight  viruses is using messenger RNAbeing  

  • deployed for the first time to fight SARS  CoV-2, the virus that causes Covid-19.

  • To make an mRNA vaccine, experts  start by sequencing the viral  

  • genome and finding the instructions  for how it binds to healthy cells.  

  • For SARS CoV-2, it turns out that it binds using  spike proteins that stud the virus's surface.

  • Then, scientists copy and package those  genetic instructions and inject them into  

  • healthy volunteers, so cells in their body  will start producing their own spike proteins  

  • (but not attached to any virus). That waypatients create their own blueprint of a  

  • critical piece of the virus for their immune  systems to learn to identify and neutralize.

  • mRNA vaccines haven't been widely used beforemostly because it's hard to keep artificial  

  • messenger RNA intact long enough to reach host  cells. But scientists have overcome that hurdle  

  • with new technology (particularly, synthesizing  better enzymes to flank the blueprint sequences)  

  • and now they're able to make vaccines incredibly  fast. For SARS-CoV-2, they also made changes to  

  • the RNA so it produced a very stable version of  the spike protein, one the immune system could  

  • easily recognize--the natural virus spike  kind of wobbles around in a confusing way..

  • Researchers were able to synthesize  RNA for the SARS-CoV-2 vaccine  

  • within a week of sequencing the  virus' genome, back in January 2020.  

  • That allowed them to start the first phase  of drug trials by March of last year.

  • Vaccines aren't miracle cures: they don't  make every individual immune to disease.  

  • But what matters is that they  work on a population level.

  • The key to a successful vaccination program is  immunizing enough people to develop so-called  

  • herd immunity,” where most infected individuals  can't spread it to anyone else. This way,  

  • over time, fewer and fewer people get infectedideally until the disease is wiped out entirely.

  • Diseases still pose a risk as long  as there are some cases anywhere.

  • This year, we're witnessing the largest  international vaccine development effort ever.  

  • SARS-CoV-2 showed how quickly diseases  can spread in our globalized world.  

  • Now we're about to find out  if the vaccination techniques  

  • we've developed over centuries are  sufficient to meet the challenge:  

  • whether we can develop global herd immunityor if many countries will continue to struggle.

  • It's not just about emerging from this pandemic,  

  • but about creating a fast and effective  strategy to deal with future contagions.  

  • They may be inevitable, given how many viruses  seem poised to jump from animals to humans.

  • For now, and the upcoming decades,  

  • vaccines will likely be the key to ensuring our  collective wellbeing, and perhaps our survival.

Vaccines are medicines that train the body  to defend itself against future disease.

字幕と単語

動画の操作 ここで「動画」の調整と「字幕」の表示を設定することができます

B2 中上級

Decoded: How do vaccines actually work?

  • 8 1
    joey joey に公開 2021 年 05 月 15 日
動画の中の単語