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UCSD Researchers Estimate COVID-19 Was Around 2 Months Before First Reports

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Using molecular dating tools and epidemiological simulations, researchers at UC San Diego estimate that the SARS-CoV-2 virus was likely circulating undetected for at most two months before the first human cases of COVID-19

Speaker 1: 00:00 From potential treatments to how it affects the human body that COVID-19 virus has been characterized by how rapidly our understanding of it has evolved. Now, a new report from the UC San Diego school of medicine could change what we know about the origins of COVID-19 and how long it's been circulating among humans. Joining me to discuss this research is senior author Joel worth. I'm an associate professor in the division of infectious diseases and global public health at the UC San Diego school of medicine. Joel, welcome.

Speaker 2: 00:32 Hi, thanks for having me. Your research

Speaker 1: 00:34 Indicates that the novel coronavirus was circulating months before originally thought what pushed you and your team to further investigate the timeline of this virus?

Speaker 2: 00:44 Well, there were lots of reports, uh, of the virus outside of China in the fall of 2019. And even actually going back, uh, into early 2019 from all over the world. And what we wanted to answer was how far back was it biologically possible for this virus to have been in China and for us not to have seen it and for it not to have left its Mark in the genetic material of the virus itself. So that day of middah Tober that we say that's really an upper bound. It could have happened after that, but we really wanted to put an upper limit on how long the virus could have been circulating in China before it was discovered.

Speaker 1: 01:24 And what are the major implications of these findings?

Speaker 2: 01:28 The one thing it tells us that this virus was likely around for a while before it was discovered, which just highlights the difficulty in detecting highly transmissible pathogens that don't have exceptionally high mortality rates. One of the most surprising findings that came out of our study was that when we tried to simulate the beginnings of the Corona virus pandemic, the majority of our simulated epidemics went extinct in seven out of 10 tries. We were unable to generate a pandemic, which means that this virus more often than not would have gone extinct on its own.

Speaker 1: 02:03 Do you think this particular Corona virus became a global pandemic?

Speaker 2: 02:07 The most nefarious thing about SARS cov two is that it can transmit during the asymptomatic period. So we weren't able to contain it because people got on planes and trains and cross borders, uh, even with no evidence of infection. And by the time we realized that, uh, the virus that early, already firmly ensconced itself, uh, across the globe,

Speaker 1: 02:31 How does knowing the timeline of the virus help us understand its origin?

Speaker 2: 02:36 Well, in the beginning of the pandemic, there was a lot of talk about it coming from the market, meaning that that market and Wu Han was the place of cross species transmission. Now, knowing that there are earlier cases in December in Wu Han, that aren't linked to the market and the genetic ancestor predating those. And then our analysis says, well, it could have even been around for a couple of weeks or even up to a month before that time point tells us that we don't really have a good idea of where the first person who got infected was we have a good idea where the first big clusters were, but those first people before you had large, super spreading events, still remain a mystery

Speaker 1: 03:19 To come to this conclusion, your team use something called molecular clock, evolutionary analysis. Can you explain what this technique is and how it works?

Speaker 2: 03:29 Yeah, so the molecular clock is a really important tool for investigating, uh, the history of viruses and their transmission. Basically it allows us to count up mutations that separate viruses sampled over time in this case in China. And by counting up those mutations over time and seeing how quickly they happen, we can estimate the age of a virus that we never saw the ancestor say all of the viruses that were in China.

Speaker 1: 04:00 And can this data be used to prevent the spread of highly transmissible diseases in the future?

Speaker 2: 04:05 Sure. Well, we're using this technique right now to track, uh, the variance of SARS cov two around the world, looking at their emergence and spread. So it's as important to the beginning of the pandemic as it is to today.

Speaker 1: 04:20 Origins of this virus have been politicized with racist rhetoric, notably from former president Trump followed by an increase in violence and racism against Asian-Americans and Pacific Islander Americans as a scientist. I wonder if you have some thoughts on how focusing on the science can help us overcome the racist blaming that's taken place in the last year.

Speaker 2: 04:42 Absolutely. It's quite unfortunate. And seeing how this virus spreads and how readily it's spread you realize that this isn't the fault of a particular geographic region or people has really taken over the world and doesn't respect national borders or racial identity. It's also important how we've named this virus SARS cov two, um, after, uh, the type of virus it is and the type of illness it causes, we used to name viruses, uh, after locations. And there's been a concerted move away from that in the field. Um, partly to respect, uh, that viruses aren't the fault of one particular region or people. One early example of corrective naming was with the syndrome, brave virus, which is a haunted virus found in the four corners region. And in order to avoid stigmatizing any given population, uh, they gave it the no name virus rather than, uh, identifying a particular geography or, uh, people that lived there. And for you,

Speaker 1: 05:50 From everything that you know about viruses, is this one acting like a normal metric?

Speaker 2: 05:55 Yes. Uh, I have no specific reason to suspect that this virus came out of a lab. Coronaviruses jumped into humans all the time, and this is a very unfortunate, but apparently a natural phenomenon that we as humans are going to have to increasingly prepare to live with.

Speaker 1: 06:16 I've been speaking with Joel worth. I'm an associate professor in the division of infectious diseases and global public health at the UC San Diego school of medicine. Joel, thank you very much for joining us.

Speaker 2: 06:27 Thank you for having me.

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