**2. The coronavirus disease 2019 (COVID-19) pandemic**

In Wuhan, Hubei Province, China in December 2019, pneumonia of an unknown origin started affecting index cases linked to a local wholesale food market [5]. Respiratory samples collected from these patients were subjected to genomic analysis, and the virus responsible was discovered to be a novel coronavirus related to Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV). It was therefore named SARS-CoV-2, and the disease it causes was named coronavirus disease 2019 (COVID-19) [3, 5]. Due to its high infectivity, the novel coronavirus began spreading rapidly around the globe, leading the World Health Organization (WHO) to declare COVID-19 as a pandemic disease in March 2020 [6]. As of July 3, 2021, the total number of cases of COVID-19 in the United States was 33,530,880, including 15,555 new cases [7]. To date, more than 1,000,000 patients have died from COVID-19 in the United States alone [7].

In comparison, the 1918 Spanish influenza pandemic was caused by the H1N1 influenza A virus and lasted from 1918 to 1920 [8]. It disproportionately affected healthy, 25-40 years old individuals, who accounted for 40% of mortalities. By the end, the H1N1 pandemic was responsible for 50 million deaths worldwide [8]. In contrast, COVID-19 primarily affects people over the age of 65, especially those with comorbidities [8]. Although the overall mortality rate is very similar between the two pandemics - 2.5% for H1N1 and 2.4% for SARS-CoV2 - the mechanisms for mortality differ [8]. Whereas H1N1 tended to cause secondary bacterial pneumonia, SARS-CoV-2 resulted in an overactive immune response resulting in multiple organ failures [8]. The mean time to death for the H1N1 influenza was 2 weeks whereas it is 25 days for SARS-CoV2 [9, 10]. The latter finding is also responsible for the significant resource utilization (including intensive care utilization) related to COVID-19 cases.

Similar to the 1918 H1N1 pandemic, governments across the world implemented lockdown and quarantine strategies to contain the spread of COVID-19 [11]. In early 2020, many countries started implementing stay-at-home orders and sometimes more extensive shutdowns that mandated the closure of all non-essential businesses with concurrent stay-at-home orders to help minimize the spread of COVID-19 and to prevent hospitals from being overrun with COVID-19 patients [6, 12]. Additionally, universal masking mandates were put in place and there were physical distancing rules to maintain interpersonal distance of at least 6 feet between individuals when in public [5]. While these measures helped to contain the spread of COVID-19, they also had negative public health effects related to adverse childhood experiences (ACE, see later section) as well as TS [6].
