ARI SHAPIRO, HOST:
Scientists hope to have an effective coronavirus vaccine by the end of the year, but their efforts could be undercut if the virus changes in a way that lets it evade the vaccine. NPR's Jon Hamilton reports on how researchers are monitoring the coronavirus from mutations that might spell trouble.
JON HAMILTON, BYLINE: The best way to spot mutations or genetic changes in a virus is by comparing all the genes in different samples. Peter Thielen of Johns Hopkins Applied Physics Laboratory says back in January, scientists had only one whole genome sequence to study.
PETER THIELEN: Today we have over 47,000 coronavirus genomes that have been submitted to international databases.
HAMILTON: New genomes are added every day from all over the world. And Thielen says each time a new one arrives, it gets a close examination.
THIELEN: What we're looking for in the data is similarity between the virus that first emerged and the genome that had been deposited and any changes that have occurred in the virus.
HAMILTON: Overall, he says, the viruses circulating today look remarkably similar to the ones that appeared in China late last year. SARS-CoV-2 simply isn't mutating very quickly. Thielen says that's partly because when the virus generates copies of itself, it uses a sort of proofreading system to catch any errors in the genetic code.
THIELEN: So if there's a change, it will actually make a correction at a specific location.
HAMILTON: Preventing a mutation. Vaccine developers are especially concerned about locations that affect something called the spike protein. It's a structure on the surface of the coronavirus that allows it to invade cells. And the goal of current vaccines is to teach the immune system to recognize this spike protein and repel the virus. Thielen says so far, that's looking like a good strategy.
THIELEN: The targets for diagnostics and the targets for vaccine design still today remain the same as we would've designed them in January.
HAMILTON: Some other viruses have proved less amenable. Emma Hodcroft, a molecular epidemiologist at the University of Basel in Switzerland, says the influenza virus is constantly altering its surface proteins.
EMMA HODCROFT: Flu just really loves to change these parts. It even swaps them around kind of within the flu family. And that's why we can end up with such different flus from season to season.
HAMILTON: Flus that can dodge the previous year's vaccine. Hodcroft says measles represents the other extreme. Children today get a measles vaccine that was developed in the 1960s and protects for a lifetime. She says SARS-CoV-2 is likely to fall somewhere between the flu and measles when it comes to developing a vaccine.
HODCROFT: I think in the short term, we'll find something. I think the big question is whether this is something we'll be able to vaccinate once and then you never have to get it again, or will it be something you have to get every couple of years to keep your immunity up to date.
HAMILTON: Hodcroft says scientists are unsure because the coronavirus is so new.
HODCROFT: We haven't really seen the full diversity of how the virus can mutate because it gathers mutations over time. We can't speed up time, so we just have to wait and see how it's mutating.
HAMILTON: Even if the coronavirus doesn't change much, it's not clear how long the immune system will remember what it's learned from a vaccine. But Hodcroft says at the moment, vaccine developers have more pressing concerns.
HODCROFT: It's not a small feat to manufacture a vaccine for billions of people and then to get it to all of those people. And I think we have to keep in mind that even that is going to take months.
HAMILTON: In addition to the months required to develop a safe and effective vaccine in the first place.
Jon Hamilton, NPR News.
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