The COVID-19 pandemic in the USA: what might we expect?
Authors: Gerardo Chowell, Kenji Mizumoto
Journal: The Lancet (2020)

As of March 19, 2020, 191 127 cases of, including 7807 deaths attributed to, coronavirus disease 2019 (COVID-19) have been reported worldwide.1WHOCoronavirus disease 2019 (COVID-19): situation report—58. World Health Organization, 2020https://www.who.int/docs/default-source/coronaviruse/situation-reports/20200318-sitrep-58-covid-19.pdf?sfvrsn=20876712_2Date accessed: March 18, 2020Google Scholar The incidence of reported cases in China has dramatically reduced to tens per day as a result of strict social distancing measures; however, the pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is now generating sustained transmission in many countries including the USA. In The Lancet, Isaac Ghinai, Tristan D McPherson, and colleagues2Ghinai I McPherson TD Hunter JC et al.First known person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the USA.Lancet. 2020; (published online March 12.)https://doi.org/10.1016/S0140-6736(20)30607-3Summary Full Text Full Text PDF PubMed Scopus (379) Google Scholar report details of the first known human-to-human transmission of SARS-CoV-2 in the USA, which was identified in late January, 2020. An infected traveller, a woman in her 60s, returned from Wuhan and subsequently became symptomatic and transmitted the infection to her husband with whom she had prolonged and unprotected contact.2Ghinai I McPherson TD Hunter JC et al.First known person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the USA.Lancet. 2020; (published online March 12.)https://doi.org/10.1016/S0140-6736(20)30607-3Summary Full Text Full Text PDF PubMed Scopus (379) Google Scholar An investigation of 350 contacts of both patients did not lead to any additional cases. However, we cannot rule out the possibility that some asymptomatic contacts went undetected, because the proportion of asymptomatic COVID-19 cases appears to be large. For example, estimated asymptomatic proportion was 18% for the outbreak on the Diamond Princess cruise ship.3Mizumoto K Kagaya K Zarebski A et al.Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020.Euro Surveill. 2020; 252000180Crossref Scopus (1588) Google Scholar In the USA, where influenza activity is still widespread,4CDCWeekly U.S. influenza surveillance report. Centers for Disease Control and Prevention, 2020https://www.cdc.gov/flu/weekly/index.htmDate accessed: March 16, 2020Google Scholar 3499 cases, including 60 deaths, have been attributed to COVID-19 as of March 15, 2020.5Johns Hopkins CSSE2019 novel coronavirus COVID-19 (2019-nCoV) data repository by Johns Hopkins CSSE. GitHub, 2020https://github.com/CSSEGISandData/COVID-19/blob/master/csse_covid_19_data/csse_covid_19_time_series/time_series_19-covid-Confirmed.csvDate accessed: March 15, 2020Google Scholar Most cases have been reported in New York (20·1%), Washington (18·4%), and California (12·2%), but the epidemic is still unravelling as testing becomes broadly available across the country. Although it is impossible to predict which areas of the USA will fare better or worse with regard to COVID-19, past influenza pandemics in the USA have generated substantial spatial heterogeneity in mortality.6Murray CJ Lopez AD Chin B Feehan D Hill KH Estimation of potential global pandemic influenza mortality on the basis of vital registry data from the 1918-20 pandemic: a quantitative analysis.Lancet. 2006; 368: 2211-2218Summary Full Text Full Text PDF PubMed Scopus (486) Google Scholar For example, all-cause mortality for the 1918–20 influenza pandemic ranged from 0·25% in Wisconsin to 0·84% in Arizona.6Murray CJ Lopez AD Chin B Feehan D Hill KH Estimation of potential global pandemic influenza mortality on the basis of vital registry data from the 1918-20 pandemic: a quantitative analysis.Lancet. 2006; 368: 2211-2218Summary Full Text Full Text PDF PubMed Scopus (486) Google Scholar, 7Dahal S Jenner M Dinh L Mizumoto K Viboud C Chowell G Excess mortality patterns during 1918-1921 influenza pandemic in the state of Arizona, USA.Ann Epidemiol. 2018; 28: 273-280Crossref PubMed Scopus (24) Google Scholar Furthermore, older populations in some areas tended to exhibit lower excess mortality, which might have resulted from protection provided by previous exposure to a similar virus.8Olson DR Simonsen L Edelson PJ Morse SS Epidemiological evidence of an early wave of the 1918 influenza pandemic in New York City.Proc Natl Acad Sci USA. 2005; 102: 11059-11063Crossref PubMed Scopus (214) Google Scholar In contrast, the risk of death from COVID-19 increases with older age,9Zhou F Yu T Du R et al.Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study.Lancet. 2020; (S0140-6736(20)30566-3.)Summary Full Text Full Text PDF Scopus (18962) Google Scholar suggesting that Florida, Maine, and Puerto Rico, which have the populations with the largest proportions of older people (≥65 years), might be the most vulnerable to this pandemic virus. On March 13, 2020, President Donald Trump declared a national emergency to combat the spread of COVID-19 in the USA, which led to a range of social distancing interventions across the country, including closures of schools, bars, cinemas, and restaurants, cancellation of large public gatherings, including cultural and sporting events, and discouraging gatherings of more than 50 people. Moreover, an increasing number of businesses and companies have asked their employees to work remotely. These social distancing measures are reducing the transmission rate of the virus and, in turn, reducing the risk of death for the most vulnerable populations. During the influenza 2009 A/H1N1 pandemic, the implementation of social distancing interventions, including nationwide school closures and cancellation of public gatherings, was associated with a 30% reduction in the transmission rate.10Chowell G Echevarría-Zuno S Viboud C et al.Characterizing the epidemiology of the 2009 influenza A/H1N1 pandemic in Mexico.PLoS Med. 2011; 8e1000436Crossref PubMed Scopus (184) Google Scholar However, it increased after the mandatory school suspension resumed and before summer vacation started.10Chowell G Echevarría-Zuno S Viboud C et al.Characterizing the epidemiology of the 2009 influenza A/H1N1 pandemic in Mexico.PLoS Med. 2011; 8e1000436Crossref PubMed Scopus (184) Google Scholar Given the uncertainties surrounding the extent of the COVID-19 pandemic across the country, efforts to sustain online learning and remote working in combination with enhanced infection control measures in health-care settings and nursing homes could aid in mitigating the spread of the virus and gaining control of the epidemic's chains of transmission. In the USA, past influenza pandemics have spread as a series of waves of varying durations and intensities, which have been associated with seasons and school cycles.10Chowell G Echevarría-Zuno S Viboud C et al.Characterizing the epidemiology of the 2009 influenza A/H1N1 pandemic in Mexico.PLoS Med. 2011; 8e1000436Crossref PubMed Scopus (184) Google Scholar, 11Chao DL Halloran ME Longini Jr, IM School opening dates predict pandemic influenza A(H1N1) outbreaks in the United States.J Infect Dis. 2010; 202: 877-880Crossref PubMed Scopus (115) Google Scholar Because respiratory viruses, including other coronaviruses, are known to respond to seasonal variation,12Neher RA Dyrdak R Druelle V Hodcroft EB Albert J Potential impact of seasonal forcing on a SARS-CoV-2 pandemic.medRxiv. 2020; (published online March 3.) (preprint).DOI: 10.1101/2020.02.13.20022806Google Scholar we might expect that increasing temperatures in the summer could reduce the intrinsic transmissibility of the novel coronavirus to some extent. In the context of a novel virus, warmer weather alone is unlikely to sufficiently mitigate the transmission rate and interrupt community transmission in the absence of social distancing strategies. Perhaps the most reasonable scenario ahead of us is that the transmission rate will decline during the next few months, partly driven by social distancing measures, a scenario that is reminiscent of the influenza 2009 A/H1N1 pandemic.10Chowell G Echevarría-Zuno S Viboud C et al.Characterizing the epidemiology of the 2009 influenza A/H1N1 pandemic in Mexico.PLoS Med. 2011; 8e1000436Crossref PubMed Scopus (184) Google Scholar Close monitoring of the transmission potential of the virus on the basis of reliable and publicly available data in near real-time will be key to short-term forecasts and sound public health decisions. We declare no competing interests. First known person-to-person transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the USAPerson-to-person transmission of SARS-CoV-2 occurred between two people with prolonged, unprotected exposure while Patient 1 was symptomatic. Despite active symptom monitoring and testing of symptomatic and some asymptomatic contacts, no further transmission was detected. Full-Text PDF