Here's something I once learned in virology school that should make you feel a bit better about why, unlike the flu, #COVID19 most likely won't be able to mutate to escape the vaccines we're developing. It has to do with the fact that COVID-19's genome is made up of...
...just one long strand of genetic material. That makes it an "unsegmented" virus. Its genomic code fits on one page. The genome describes the virus and provides instructions for how to make more of that virus. When a virus gets into the cell, it accesses machinery for both...
...making copies of its genome & following its own instructions for making other parts that assemble into more viruses. The flu virus, however, has 8 genomic segments. Its code fits on 8 pages. That's not common for viruses and it gives the flu a special ability.
Because the major parts of the flu virus are described on separate pages (segments) of its genome, when two different flu viruses infect the same cell, they can swap pages. In this case, the flu virus is like one of those avatars you make in an app where you can...
mix & match a character's shirt, pants, nose, hair, etc to create different looks. That page swapping process where viruses exchange parts of their genome is called recombination. Think of it this way... imagine two people with 8-page reports fighting over a copy machine.
In the fight, some copies might turn out to have a mix of pages from their reports. A mixed report might have Page 1 from report A and pages 2-8 from report B. It's easy to see how flu can change it looks easily when multiple flu strains pass through the same host, esp animals.
But coronavirus is just a one-page report. That page tends to stay together and it takes a pretty weird situation for the top half of report A to end up fused to the bottom half of report B. The pages would need to tear at similar spots.
That's also called recombination and it happens, but it's much rarer and harder than two 8-page reports swapping pages, which happens more often with flu viruses.
But both flu & coronoviruses mutate another way I can best describe as typos that are introduce by the copy machines. Think of the copy machine as more of a scanner that transcribes the image of the page into text (ever use software that does that?), introducing typos where...
...a bit of smudged ink makes an "i" look like an "l". The bad scanner with bad transcription software then prints out the reprocessed text on a bad printer which introduces more smudges... and then the scanner scans that new page, makes more mistakes, prints again, etc.
These mutations in the code cause features of the virus to change gradually, a process called "drift". When it swaps pages entirely with a different flu virus, we call that "shift". Drift through typos tends to cause small changes. Shift through recombination causes bigger ones.
To the extent that the flu virus we see one year is only slightly different than the ones we've seen in recent years, our immune systems are at least partially prepared and so we are partly protected and, if we get sick, it might be milder.
Some years, the flu swaps out a page with a less familiar strain (e.g. one from 10 years ago) & we have to hope the vaccine is well-matched to that strain to protect ourselves or else we suffer a bad flu season since our immune system is less ready to fight it off.
But when the flu suddenly puts on a radically different face it picked up b/c it swapped a page w/ a bird or pig flu strain that most people haven't seen and to which we don't have a vaccine, that virus can evade our herd immunity entirely, cutting through all of us unopposed.
That's a pandemic. COVID-19 was brewing within bats for a long time, mutating into its current form through typos &, to a less extent, rare recombination events among coronaviruses...
and now that it's here, it's as new to us as a shifted flu strain that we've never seen before, and it's causing a pandemic. But once it's torn through our population or, better still, we've developed a vaccine to this strain (and all taken it!), we'll have herd immunity to it.
And while that immunity will likely fade & need reboosting periodically with likely same vaccine from year to year (e.g. as is case for most vaccines; e.g. measles vaccine doesn't change), COVID19 won't be able to mutate away from our vaccines nearly as rapidly as flu can...
...b/c COVID19's genome is unsegmented (one page)... & it can't pull off the face-swapping tricks flu can w/ its 8-page segmented genome. Now some will point out data that the virus is already mutating. It is.
But it's not mutating in ways that are significant enough to rapidly evade immunity from a vaccine (not like flu). So don't let big, multi-branched graphs that track every little mutation make you think we'll have to develop a new COVID19 vaccine each year. It's simpler than flu.
I hope you found this trivia cool & a bit reassuring. Teach that to the kids you'll be homeschooling for a while. Hope they become virologists. Learn more here... ncbi.nlm.nih.gov/books/NBK8439/
Thank you to the virologist at a company that's now working on a vaccine who reminded me of this key difference between coronavirus & flu when I asked them if they were planning to have to adapt their vaccine annually. Scientists in labs go unrecognized yet should be celebrities.
...[caught an error- swapping segments/pages is actually called “re-assortment”. Only rarer splicing of segments (top half of A w/bottom half of B) is recombination. Not important for understanding this thread but still gotta get it right.]...
Someone pointed out that coronaviruses still mutate & could evolve away from a vaccine, even if slowly. That’s true. But we’ll have lots of time to keep up w/ it & adapt the vaccine... flu gives us a heads up of a few months. Coronavirus would likely be years. still reassuring.
Someone forwarded me this article in which a molecule geneticist makes the same case that virus likely won't evolve quickly away from a vaccine. washingtonpost.com/health/the-cor…
