SARS-CoV-2 is highly contagious, but a few dozen imported cases may not be enough to trigger many large undetected outbreaks. Based on related diseases such as SARS and MERS, epidemiologists suspect that the potential spread of the corona virus is irregular. Most likely, some sick people infect many others, but most only infect a few. Alessandro Vespignani, a network scientist and public health professor at Northeastern University, estimates that in every American city that would later become a hot spot for COVID-19, maybe 10 to 20 “local transmission events” occur in January. Apart from one or two infections that spread large outbreaks in places like Seattle and New York, most infections that come from abroad in January will be transmitted to at least a few people, then quickly “fail,” Bedford tells me.
Establishing a more precise number of how many sick people who brought SARS-CoV-2 to the US earlier this year will require data that may be difficult or impossible to collect, especially during a major global health crisis. For one: how many people are really sick with COVID-19 worldwide in January (or earlier). Official data from Wuhan has been unreliable from the start. And countries that have since stepped up efforts to detect their corona virus did not look for cases carefully at the beginning of the year. The World Health Organization does not declare a global health emergency until January 30.
Researchers also need to know where people travel around the world in the early weeks of the pandemic. “One of the big challenges in seeing the true global spread of this disease is that, since January, travel patterns have been massively disrupted,” Gardner said. When researchers do not have perfect travel data for the time and place they are studying, he explained, they often replace or extrapolate from past data. “Sometimes you can say,” Yes, I don’t have 2016 data, but I use 2015 data. That representative. ‘That is no longer valid. “The Chinese government closed Wuhan on January 23; even before that, individual movement patterns might begin to shift in ways that are difficult to trace.
When the living cannot be fully accounted for, one way to move forward is to count deaths. Testing the deficiencies meant that some COVID-19 deaths were not detected, but researchers could better handle how many people were killed by the virus over a certain period of time by looking at excess mortality: how many more people died than expected under normal circumstances.
Last week, the National Center for Health Statistics publish preliminary data about excess weekly deaths since January 2017, which will be renewed when the pandemic starts. Bob Anderson, head of the NCHS mortality statistics branch, told me that this was “the first time we have done something like this before the data is final.” The hope is that researchers can use gross figures to estimate how many Americans died from COVID-19 during a certain period, and from there estimate how many Americans were infected. But choosing excess deaths in the first few weeks of the year will be difficult. Compared to the hundreds of thousands of deaths experienced by the country in an ordinary month, some COVID-19 deaths will hardly be a blip. Indeed, according to NCHS calculations, the United States did not exceed the expected number of deaths by a significant difference until the week of March 22.