1.The object-to-human transmission route of SARS-CoV-2 At the time of writing,coronavirus disease 2019(COVID-19),which is caused by the severe acute respiratory syndrome coron-avirus 2(SARS-CoV-2),has been a global pandemic for more than a year.As of 22 September 2021,the global cumulative incidence exceeds 229 million cases,and the number of deaths has exceeded 4.75 million[1].The current situation of epidemic prevention and control within the countries around the world can be roughly divided into two stages:the pandemic stage that the United States,the United Kingdom,and India are still experiencing(as of 23 September 2021,newly reported cases in the last 24 h in the United States,United Kingdom,and India are 202840,31095,and 26964,respectively[1]);and the normalized epidemic pre-vention and control stage that countries such as China and New Zealand are currently in.
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