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  • 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.


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Decoded: How do vaccines actually work?

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    joey joey に公開 2021 年 05 月 15 日