From How the 2009 H1N1 Pandemic Compares with COVID-19:<p><a href="https://www.bloomberg.com/opinion/articles/2020-03-10/how-coronavirus-compares-with-2009-s-h1n1-in-spread-and-Freaction" rel="nofollow">https://www.bloomberg.com/opinion/articles/2020-03-10/how-co...</a><p>For example: Why was H1N1 allowed to spread around the world more or less unchecked, while countries are going to far greater lengths to try to halt Covid-19? Why did the WHO call H1N1 a pandemic but not Covid-19? Isn’t 12,469 deaths a lot worse than the 26 that have been attributed to Covid-19 in the U.S. so far?<p>That last one is the simplest to answer: Covid-19 is near the beginning of its spread in the U.S., and thus cannot be compared with H1N1’s effect over a full year. If the U.S. death toll from Covid-19 is only 12,469 a year from now, that will likely be counted as a great success. The legitimate worry is that it could be many, many times higher, because Covid-19 is so much deadlier for those who get it than the 2009 H1N1 influenza was.<p>How much deadlier is still unknown, but of the cases reported to the WHO so far 3.4% have resulted in fatalities. That’s probably misleadingly high because there are so many unreported cases, and in South Korea, which has done the best job of keeping up with the spread of the virus through testing, the fatality rate so far is about 0.7%. But even that is 35 times worse than H1N1 in 2009 and 2010. Multiply 12,469 by 35 and you get 436,415 — which would amount to the biggest U.S. infectious-disease death toll since the 1918 flu. Hospitalization rates are also many times higher for Covid-19, meaning that if it spread as widely as H1N1 it would overwhelm the U.S. health-care system.<p>That’s one very important reason governments (and stock markets) around the world have reacted so much more strongly to Covid-19 than to the 2009 H1N1 pandemic. Another reason is somewhat more hope-inspiring. It’s that public health experts generally don’t think influenza can be controlled once it starts spreading, other than with a vaccine, whereas several Asian countries seem to have successfully turned back the coronavirus tide, for now at least.<p>Influenza can’t be controlled because as much as half the transmission of the disease occurs before symptoms appear. With Covid-19 that proportion seems to be lower, meaning that even though it’s more contagious than influenza once symptoms appear, it may be possible to control by testing widely and quickly isolating those who have the disease.