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Like many epidemiologists, I have for the last 15 months been intensely focused on COVID-19. One of the most surprising aspects of this work has been the constant, often aggressive, criticism directed at my field — from insinuations that epidemiologists aren't smart enough to grasp key issues (compared with, say, economists) to drive-by attacks on Twitter suggesting we are somehow profiting from or delighted by COVID-related restrictions.

My research focuses on methods for doing epidemiology: how it works, why it sometimes doesn't, and how best to use evidence to make reliable public health decisions. I'm very interested in understanding what we got wrong about COVID and why, and I would be among the first to admit that we didn't get everything right. At the same time, the caricature of the field presented by its most vociferous critics is unrecognizable to me, so it's worth attempting some kind of accounting of how we've done.

One place to start would be admitting my own mistakes. I saw the first report of "pneumonia of unknown cause" on Dec. 31, 2019, and knew this was something to pay attention to. But throughout January, I was only mildly concerned. I believed COVID would be contained relatively quickly with case counts similar to those for SARS in 2003 (which ultimately infected about 8,000 people, that year). When dealing with a brand new infectious disease, the most reasonable decision-making approach is to draw an analogy to a more familiar disease. SARS-CoV-2, the virus that causes COVID-19, is very similar to the SARS virus. Both had fairly high mortality and seemed similarly infectious.

What's more, SARS was only transmissible after patients started to show symptoms, and most cases were quite severe, so they were easy to detect. So, in January, it was reasonable to assume the precautions that worked for SARS would work for the novel coronavirus — namely, isolation of symptomatic individuals, quarantine for anyone exposed, contact tracing and high-quality protective equipment for medical personnel. Unfortunately, the analogy was imperfect: Widespread asymptomatic and pre-symptomatic transmission, we soon learned, meant COVID was much harder to contain than SARS.

In February 2020, I was becoming concerned about spread outside China, but still believed a program of testing, contact tracing, and isolation or quarantine would be sufficient to control COVID-19 in the United States. This was reasonable. Such a strategy did work in many countries: Mongolia, Vietnam, New Zealand and South Korea all successfully controlled COVID with this approach early in 2020. Similarly, Australia, which had a large initial outbreak, was able to almost eliminate COVID through contact tracing and targeted state-level lockdowns. So I wasn't wrong that it could have worked.

But I failed to anticipate the two big reasons it didn't work here. First, I never expected the Centers for Disease Control to release flawed tests. We spent far too long without adequate testing, unable to track the spread of infection. Accurate tests only become widely available after Feb. 29, when the Food and Drug Administration lifted restrictions preventing state and commercial labs from developing their own diagnostic tests.

Second, I didn't count on the prolonged reliance on symptom-based testing. Even after reliable tests became available, symptom-based testing meant that we may have missed up to 30% of infections in the spring of 2020. Unfortunately, although epidemiologists have called for broader testing for over a year now, symptom-based testing is still the primary model used in much of the country and continues to limit our ability to control COVID.

Then there is the infamous mask issue. Epidemiologists have taken a lot of heat on this question in particular. Until well into March 2020, I was skeptical about the benefit of everyone wearing face masks. That skepticism was based on previous scientific research as well as hypotheses about how COVID was transmitted that turned out to be wrong. Mask-wearing has been a common practice in Asia for decades, to protect against air pollution, and to prevent transmitting infection to others when sick. Mask-wearing for protection against catching an infection became widespread in Asia following the 2003 SARS outbreak, but scientific evidence on the effectiveness of this strategy was limited.

Before the COVID-19 pandemic, most research on face masks for respiratory diseases came from two types of studies: clinical settings with very sick patients, and community settings during normal flu seasons. In clinical settings, it was clear that well-fitting, high-quality face masks, such as the N95 variety, were important protective equipment for doctors and nurses against viruses that can be transmitted via droplets or smaller aerosol particles. But these studies also suggested careful training was required to ensure that masks didn't get contaminated when surface transmission was possible, as is the case with SARS. Community-level evidence about mask-wearing was much less compelling. Most studies showed little to no benefit to mask-wearing in the case of the flu, for instance. Studies that have suggested a benefit of mask-wearing were generally those in which people with symptoms wore masks — so that was the advice I embraced for the coronavirus, too.

I also, like many other epidemiologists, overestimated how readily the novel coronavirus would spread on surfaces — and this affected our view of masks. Early data showed that, like SARS, the coronavirus could persist on surfaces for hours to days, and so I was initially concerned that face masks, especially ill-fitting, homemade, or carelessly worn coverings, could become contaminated with transmissible virus. In fact, I worried that this might mean wearing face masks could be worse than not wearing them. This was wrong. Surface transmission, it emerged, is not that big a problem for COVID, but transmission through air via aerosols is a big source of transmission. And so it turns out that face masks do work in this case.

I changed my mind on masks in March 2020, as testing capacity increased and it became clear how common asymptomatic and pre-symptomatic infection were (since aerosols were the likely vector). I wish that I and others had caught on sooner — and better testing early on might have caused an earlier revision of views — but there was no bad faith involved.

If I was wrong about COVID-19 gaining a strong foothold in the United States, I was right in my predictions after it did so. Based on everything we know about respiratory diseases, many epidemiologists predicted a large surge through the fall and winter if we didn't take adequate precautions. I spent much of the summer and fall trying make that prediction false, advising school boards about the risks and writing articles about why airborne transmission makes schools particularly hard to keep safe. But as schools opened in August and September — not to mention bars and restaurants — cases rose and rose and rose. This winter surge looked almost exactly as I feared it would.

Unlike many other prominent epidemiologists, physicians, and public-health experts, I think the decision to open schools and colleges in the fall was the wrong move — and I argued against it. It's undeniable that conflicting opinions about opening schools have caused a significant rift in the epidemiology and public health community, one we will be grappling with for some time. Weighing the trade-offs — COVID risk versus losing a year of education — is not an easy matter, and there likely isn't a one-size-fits-all solution.

Reflecting on the past year, I would like to think the mistakes I made were honest ones, understandable errors caused by a lack of information. But not all the mistakes made during this pandemic can be described that way. Time after time, we've seen states and localities lifting COVID restrictions too soon and triggering new waves of cases, failing to learn from experience. We've also seen people protesting face-mask mandates — long after the efficacy of masks was clear — by gathering in large, noisy crowds, a setting with a high risk of COVID transmission. The worst mistakes of the pandemic, it seems clear, have come from political leaders flouting the advice of epidemiologists, not from errors made by scientists.

The COVID-19 pandemic has catapulted epidemiologists into the national spotlight. This was a new experience for most of us; we'd been used to no one knowing what our field is. Our harshest critics have suggested that we enjoy the attention, and, perversely, that we will therefore miss the pandemic. Yes we did enjoy the attention — for about an hour. And then we got back to working around-the-clock to help keep the public safe. We're exhausted and we're way past ready for this pandemic to end. As we work toward that goal, we should acknowledge our mistakes — but reject the caricature of the field presented by our critics.

Eleanor Murray is an epidemiologist and assistant professor at the Boston University School of Public Health. This piece was written for The Washington Post.

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