Virus Variants and the Pandemic
How Can a Pandemic End? – Visual Description Transcript
[Animation of a group of rabbits on green fields.]
NARRATOR: Imagine a field of rabbits. Rabbits as far as the eye can see. Like hundreds of millions of rabbits.
[Rows and rows of rabbits arise in the background.]
NARRATOR: In the early 20th century, there was just such a thing in Australia.
[The camera pulls back, and the field of rabbits is bounded by a map of Australia.]
NARRATOR: About 50 years after a few pairs were introduced, rabbits had infested the continent, destroying crops and competing with native animals for resources.
[As a few rabbits multiply into many, green grass turns yellow and then disappears entirely.]
NARRATOR: To control this hopping population, ranchers purposely infected some with the myxoma virus.
[A group of bunnies sits together. Two in the front hop to the side, revealing in their midst a rabbit filled in with the word “MYXOMA” and illustrated virions of the myxoma virus. The virions then appear inside the bodies of all the other rabbits.]
NARRATOR: An epidemic raced through the rabbits, killing 99.8% of infected populations. But a few bunnies survived. And started having baby bunnies.
[One by one, 64 rabbits arranged in a grid morph into myxoma virions. Just before the last rabbit changes, two large bunnies appear in front. Then dozens of smaller bunnies pop up.]
NARRATOR: The next time the virus came along, 90% of the rabbits died. But again, a few bunnies made it through...
[The same grid of 64 rabbits again beings morphing into myxoma virions. This time, about 1 out of 10 rabbits doesn’t change into a virus particle. A few bunnies hop through the scene.]
NARRATOR: Until the virus came back. But this time, about half of the rabbits survived.
[Three large myxoma virions move from right to left across the screen, revealing a new version of the 8x8 rabbit grid. This time, only about half the rabbits turn into myxoma virions.]
NARRATOR: At least for a while, the rabbits became more resistant with every cycle and the virus less destructive. This was natural selection unfolding over a relatively short amount of time…
[Alternating groups of myxoma virions and rabbits appear on screen—first myxoma taking prominence, then rabbits, then more myxoma, more rabbits, etc.]
NARRATOR: …and it’s one way pandemics can end: a virus doesn’t go away, but comes to a balance with its hosts, however uneasy (and occasionally still lethal) that might be.
[Teetering on either side of a seesaw are a pile of myxoma virions on the left and a group of rabbits on the right. A large virion falls down on the left, weighting the balance towards the virus. One rabbit is flung into the air, and the three remaining bunnies slide down towards the myxoma. The airborne rabbit falls back down, catching the edge of the seesaw and pulling back into precarious balance with the virion.]
NARRATOR: But is that always how pandemics end? Let’s rewind. An epidemic is what happens when a disease flares up in one area of the world.
[A silhouette stands in the center of shape that evokes a spiky coronavirus form. The virus shape expands out and other silhouettes pop up in its boundaries. The word “EPIDEMIC” appears.]
NARRATOR: A pandemic is what happens when infection rates grow exponentially, in different countries and groups of people.
[The camera pulls back to reveal a map of imaginary landforms. Dotted lines animate out to connect them, representing the spread of disease, and new virus circles arise around the map. The word “PANDEMIC” appears.]
NARRATOR: For a pandemic to start in the first place, a certain percentage of people must be vulnerable to infection and that infection has to spread easily.
[A group of people stand in the rain. One person in the middle has an umbrella. Along with the raindrops, virus shapes fall from the sky. The man with the umbrella is protected, but everyone else gets wet and their clothes are “infected” with virus shapes.]
NARRATOR: No vulnerability, no spread… no pandemic.
[The scene dissolves into the same group of people, this time all with umbrellas. They are dry and virus-free.]
NARRATOR: But let’s say we do have a deadly, transmissible, global virus—for a pandemic to end, a certain percentage of people must be immune.
[A spinning globe is surrounded by floating virus particles.]
NARRATOR: They can’t catch it and they can’t spread it, or if they do, the consequences aren’t fatal.
[The camera pans across numerous silhouettes, all holding umbrellas that shield them from virus particles. One silhouette, without an umbrella, sneezes, but the direction of her sneeze is blocked by an umbrella.]
NARRATOR: We saw that with the rabbits—over several generations, they achieved a level of resistance. The virus became what we call ‘endemic’—always hovering in the background, but not acutely devastating.
[A group of rabbits sits on a grassy lawn. Behind them, a large myxoma virion rises like a foreboding sun. The word “ENDEMIC” drops from the sky and hovers behind them.]
NARRATOR: But rabbits are notoriously speedy breeders.
[The scene transitions to a heart. Two rabbits hop from either side to meet in the middle. Dozens of small bunnies pop up around them.]
NARRATOR: If we think of a similar process evolving over human generations, it could take something like 100 to 150 years to reach that same balance point. That’s a long time and a lot of lives lost along the way.
[The camera pulls out from a wall of framed silhouettes, revealing more and more portraits. In front of the portrait wall, an elderly man looks fondly on an old photograph.]
NARRATOR: Another way to end a pandemic is containment. Things like social distancing and mask wearing cut off paths for a virus to travel.
[The word “PANDEMIC” appears on screen with menacing, tentacle-like appendages writhing around the letters. As the letters spread apart, the tentacles disappear. Then, a large surgical mask rises up, covering the letters.]
NARRATOR: And when a virus causes severe symptoms quickly, we can sometimes stop its spread.
[The word “PANDEMIC” returns with tentacles. Its letter ‘C’ changes color and develops sickly squiggles before dripping off to the ground. The longer word disappears.]
NARRATOR: This happened with SARS-CoV-1, a coronavirus closely related to SARS-CoV-2, which causes COVID-19.
[Two spiky, circular virus shapes appear—one labeled “SARS-CoV-1” and the other labeled “SARS-CoV-2.”]
NARRATOR: Patients infected with SARS-CoV-1 weren’t contagious until after they showed symptoms…
[Scenes of two people in conversation, standing and sitting. In each scene, one person’s shirt is covered in virus shapes, but the other person’s clothing remains virus-free. Then we see a man by himself, his scarf and pants covered in virus shapes. As he coughs, virus particles spread out from his body.]
NARRATOR: …so sick people could be identified and isolated. Within nine months, no new cases were being reported.
[A man lies in a hospital bed, his patient gown covered in virus particles. Two medical professionals look on through a window. The scene dissolves to the patient in a virus-free gown, standing and shaking hands with a doctor.]
NARRATOR: But that’s a pretty rare set of circumstances. Not, for example, what we’ve seen with COVID-19. It’s less lethal than the disease caused by SARS-CoV-1 but can spread before we start feeling sick.
[The same scenes of two people in conversation are repeated. This time, virus particles hover in the air between them and the second person is “infected” with the shapes.]
NARRATOR: It’s hard to contain and new enough that we don’t have immunity against it.
[The virus pattern spreads through the clothes of people standing on a crowded commuter train and sitting in a sports stadium.]
NARRATOR: So, what do we do? How does this end?
[The silhouette of a person stands before a backdrop of virus particles and question marks.]
NARRATOR: Think back to those rabbits. They developed a balance with the myxoma virus, but at great cost to their numbers. And the virus keeps evolving.
[Teetering on a seesaw are a pile of myxoma virions on the left and a group of rabbits on the right. As another virion drops onto the left-hand pile, three rabbits go flying off.]
NARRATOR: Here’s the good news—we have something the rabbits didn’t. Vaccines.
[The scene changes to a different seesaw, this time with human silhouettes on the left and SARS-CoV-2 virions on the right. The balance is precarious, until a syringe darts from above and slams down on the human side, scattering all the virions and throwing them off-screen.]
NARRATOR: Vaccines are incredible tools—shortcuts to immunity.
[A masked medical professional administers a vaccine to a masked patient.]
NARRATOR: They’ve helped us eradicate smallpox and severely limit diseases like measles and polio.
[Old posters encouraging vaccination against smallpox and measles are shown over a backdrop of various virions.]
NARRATOR: With vaccines, we can see fewer cases, fewer people severely ill, and fewer deaths.
[An abstracted bar graph shows three columns—one, representing diagnosed cases has a coughing man on top; the second, representing hospitalizations has a man in a hospital bed; and the third, representing deaths has a tombstone at the top. Each drops lower—first the case column, then the hospitalization column even more, and finally the death column drops almost to the bottom.]
NARRATOR: Hospitals won’t be so overwhelmed, and our frontline workers can breathe a little easier.
[Ambulances speed past, clearing from view and leaving a window where the sun rises over a beautiful landscape. A health care worker looks out at the scene.]
NARRATOR: But not everyone’s going to get a shot. Some people can’t for health reasons, some people don’t want to be vaccinated, and some people don’t have access to vaccines.
[A dartboard with the word “IMMUNITY” at the top. Two syringes—representing those who can’t and those who won’t get vaccinated—fly at the target but bounce off. A third syringe, representing those who don’t have access, flies past and misses the board completely.]
NARRATOR: So, we need to provide information, answer questions, and get vaccines out to everyone who wants them.
[The camera pans past three arms with band-aids, each labelled with a different word—“info,” “answers,” and “access.”]
NARRATOR: A single person can be immune, but immunity involves all of us. To really stop a pandemic, we need as many people as possible to get vaccinated.
[A person holds an umbrella upside down, forming the “U” in the word “IMMUNE.” As rain begins to fall, he opens the umbrella and the text disappears. The umbrella now stretches over other people standing around him, protecting everyone and forming the “T” in the word “IMMUNITY.” The rain stops and the person puts down the umbrella. The sun comes out.]
The COVID-19 pandemic that spread across the planet in 2020 sparked a global disaster. Then came the variants.
The Delta variant spreads faster and may cause twice as many infections as the original version. The latest identified variant, Omicron, is fast-growing with a large number of mutations that are being studied to determine whether it, too, may be a greater threat than earlier strains. And the virus is still evolving. How do these dangerous variants come about, and what can be done to stop them?
Viruses turn living cells into tiny virus-copying factories, forcing them to do the work of viral reproduction.
Viruses replicate by entering living cells and turning them into tiny virus-copying factories, forcing them to do the work of viral reproduction. “A virus is just a very, very small packet of genetic information,” says Michael Tessler, assistant professor of biology at St. Francis College and a Museum research associate.
In the case of SARS-CoV-2, the virus that causes COVID-19, this genetic material takes the form of RNA. Like its more famous double-stranded counterpart, DNA, RNA consists of a long chain of chemical components called nucleic acids. These act like letters, spelling out coded instructions for building proteins. The infected cell “reads” some of the RNA instructions and follows them, building the proteins necessary to make copies of the virus. It also replicates the virus’s RNA, the most essential piece of the new viral particle. That’s the key to viral evolution.
“Anytime there's replication, there's a certain error rate,” says Tessler. “Some percentage of the time you're going to get a change in the genetic sequence—a mutation. This is true when sperm or egg cells are made in humans. And it's true when viruses replicate as well.”
These mutations are random mistakes. “It’s like, if you were cracking eggs to make an omelet, occasionally you're going to get an eggshell in there,” Tessler explains. The mistakes might take the form of chunks of RNA omitted or duplicated, or one nucleic acid might be substituted for another. Most of these errors will be neutral or harmful for the virus, messing up its ability to replicate, for example. Virus particles with negative mutations won’t go on to infect new cells and new people.
But very occasionally, a mutation will improve the virus, and the improved variant will prosper. Improvements could include an ability to spread faster, and spread in greater numbers, as is the case with the Delta variant, says Tessler. They could include an ability to survive in warmer or colder temperatures, or at higher or lower humidity; to travel farther through the air; to delay symptoms, so that infected people feel healthy, go out with their friends, and pass the virus on. Some mutations could allow a variant to slip past the defenses of our immune system, to infect people of different ages, or even people who have been vaccinated.
Because variants can change the virus’s behavior, which in turn could affect strategies for addressing the pandemic, it’s important to detect and track variants. But the process is not straightforward. “We can't use a microscope and see the genetic code,” says Tessler. Scientists have to extract viral RNA from samples taken from people’s noses, use molecular techniques to sequence the RNA, and compare the resulting sequences to discover where they differ. This process is expensive and time consuming; most samples are never sequenced.
To find where to concentrate their efforts, scientists start by observing the behavior of the virus—noticing where it’s spreading faster, for example, or causing more deaths or hospitalizations, which may signal the arrival of a new variant. But variants aren’t the only possible explanation for differences in how the virus affects different communities. Some differences are due to biological factors, such as whether members of the community have ever before encountered the virus or a related one. Public health issues, such as levels of vaccination and masking, also play a role, as do social factors such as population density, age, access to health care, and preexisting health conditions. All these issues can make variants harder to spot.
“It takes a lot of hard work, and a lot of tracking, and a lot of comparisons to various symptoms to be able to tell when there’s a new variant, and what its characteristics are,” says Tessler.
The best way to stop dangerous variants from arising is to stop the virus from spreading. “Every time a person is infected, they're going to replicate the virus,” says Tessler. “And by replicating the virus, you're giving it another opportunity to mutate, which ultimately gives it more opportunities to evolve.”
And viruses evolve fast. Unlike, say, an elephant, which takes two years to produce a single baby, the SARS-CoV-2 virus can produce trillions of copies of itself in a single infected person—trillions of opportunities for a dangerous mutation to appear.
That’s one reason vaccination, masking, testing, and other measures that reduce the spread of COVID-19 are so important. Keeping the virus under control with vaccines and other tools doesn’t just protect individual people from illness and death. It also keeps a lid on killer variants, stopping them before they start.
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