IT'S IMPOSSIBLE TO OVERSTATE DEFLATIONARY PRESSURES:

Edward Holmes was in Australia on a Saturday morning in early January 2020, talking on the phone with a Chinese scientist named Yong-Zhen Zhang who had just sequenced the genome of a novel pathogen that was infecting people in Wuhan. The two men -- old friends -- debated the results. "I knew we were looking at a respiratory virus," recalls Holmes, a virologist and professor at the University of Sydney. He also knew it looked dangerous.

Could he share the genetic code publicly? Holmes asked. Zhang was in China, on an airplane waiting for takeoff. He wanted to think it over for a minute. So Holmes waited. He heard a flight attendant urging Zhang to turn off his phone.

"OK," Zhang said at last. Almost immediately, Holmes posted the sequence on a website called Virological.org; then he linked to it on Twitter. Holmes knew that researchers around the world would instantly start unwinding the pathogen's code to try to find ways to defeat it.

From the moment the virus genome was first posted by Holmes, if you looked, you could find a genetic component in almost every aspect of our public-health responses to SARS-CoV-2. It's typically the case, for instance, that a pharmaceutical company needs samples of a virus to create a vaccine. But once the sequence was in the public realm, Moderna, an obscure biotech company in Cambridge, Mass., immediately began working with the National Institutes of Health on a plan. "They never had the virus on site at all; they really just used the sequence, and they viewed it as a software problem," Francis deSouza, the chief executive of Illumina, which makes the sequencer that Zhang used, told me with some amazement last summer, six months before the Moderna vaccine received an emergency-use authorization by the Food and Drug Administration. The virus's code also set the testing industry into motion. Only by analyzing characteristic aspects of the virus's genetic sequence could scientists create kits for the devices known as P.C.R. machines, which for decades have used genetic information to formulate fast diagnostic tests.

In the meantime, sequencing was put to use to track viral mutations -- beginning with studies published in February 2020 demonstrating that the virus was spreading in the U.S. This kind of work falls within the realm of genomic epidemiology, or "gen epi," as those in the field tend to call it. Many of the insights date to the mid-1990s and a group of researchers in Oxford, England, Holmes among them. They perceived that following evolutionary changes in viruses that gain lasting mutations every 10 days (like the flu) or every 20 days (like Ebola) was inherently similar to -- and, as we now know, inherently more useful than -- following them in animals, where evolution might occur over a million years.

An early hurdle was the tedious nature of the work. The Oxford group had to analyze genetic markers through a slow and deliberate process that could provide insight into a few dozen characteristics of each new variant. It wasn't until the late 2000s that drastic improvements in genetic-sequencing machines, aided by huge leaps in computing power, allowed researchers to more easily and quickly read the complete genetic codes of viruses, as well as the genetic blueprint for humans, animals, plants and microbes.

In the sphere of public health, one of the first big breakthroughs enabled by faster genomic sequencing came in 2014, when a team at the Broad Institute of M.I.T. and Harvard began sequencing samples of the Ebola virus from infected victims during an outbreak in Africa. The work showed that, by contrasting genetic codes, hidden pathways of transmission could be identified and interrupted, with the potential for slowing (or even stopping) the spread of infection. It was one of the first real-world uses of what has come to be called genetic surveillance. A few years later, doctors toting portable genomic sequencers began tracking the Zika virus around Central and South America. Sequencers were getting better, faster and easier to use.

To many, the most familiar faces of this technology are clinical testing companies, which use sequencing machines to read portions of our genetic code (known as "panels" or "exomes") to investigate a few crucial genes, like those linked to a higher risk of breast cancer. But more profound promises of genome sequencing have been accumulating stealthily in recent years, in fields from personal health to cultural anthropology to environmental monitoring. Crispr, a technology reliant on sequencing, gives scientists the potential to repair disease-causing mutations in our genomes. "Liquid biopsies," in which a small amount of blood is analyzed for DNA markers, offer the prospect of cancer diagnoses long before symptoms appear. The Harvard geneticist George Church told me that one day sensors might "sip the air" so that a genomic app on our phones can tell us if there's a pathogen lurking in a room. Sequencing might even make it possible to store any kind of data we might want in DNA -- such an archival system would, in theory, be so efficient and dense as to be able to hold the entire contents of the internet in a pillowcase.

Historians of science sometimes talk about new paradigms, or new modes of thought, that change our collective thinking about what is true or possible. But paradigms often evolve not just when new ideas displace existing ones, but when new tools allow us to do things -- or to see things -- that would have been impossible to consider earlier. The advent of commercial genome sequencing has recently, and credibly, been compared to the invention of the microscope, a claim that led me to wonder whether this new, still relatively obscure technology, humming away in well-equipped labs around the world, would prove to be the most important innovation of the 21st century. Already, in Church's estimation, "sequencing is 10 million times cheaper and 100,000 times higher quality than it was just a few years ago." If a new technological paradigm is arriving, bringing with it a future in which we constantly monitor the genetics of our bodies and everything around us, these sequencers -- easy, quick, ubiquitous -- are the machines taking us into that realm.

And unexpectedly, Covid-19 has proved to be the catalyst. "What the pandemic has done is accelerate the adoption of genomics into infectious disease by several years," says deSouza, the Illumina chief executive. He also told me he believes that the pandemic has accelerated the adoption of genomics into society more broadly -- suggesting that quietly, in the midst of chaos and a global catastrophe, the age of cheap, rapid sequencing has arrived.

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