Continued proportional age shift of confirmed positive COVID-19 incidence over time to children and young adults: Washington State March—August 2020

• DOI: 10.1371/journal.pone.0243042
• Publication Date: 2021-03-24T17:33:14Z
• Authors: Judith Malmgren; Boya Guo; Henry G. Kaplan
• Keywords: Adult; Male; Adolescent; Science; Cohort Studies; 03 medical and health sciences; Age Distribution; 0302 clinical medicine; Humans; Longitudinal Studies; Child; Aged; Aged, 80 and over; SARS-CoV-2; Incidence; Q; R; Age Factors; Infant, Newborn; COVID-19; Infant; Middle Aged; 3. Good health; Child, Preschool; Medicine; Female; Coronavirus Infections; Research Article

Background As the coronavirus (COVID-19) epidemic passed initial infection peak in Washington State, phased re-opening lifted stay-at-home orders and restrictions leading to increased non-essential work, social activities and gathering, especially among younger persons.

Methods A longitudinal cohort analysis of Washington State Department of Health COVID-19 confirmed case age distribution 1) March-April 2020 (N = 13,934) and 2) March-August 2020 (N = 76,032) for proportional change over time using chi square tests for significance.

Results From March 1st to April 19, 2020 COVID-19 age distribution shifted with a 10% decline in cases age 60 years and older and a 20% increase in age 0-19/20-39 years (chi-square = 223.10, p < .001). Number of cases over the initial analysis period were 0–19 years n = 515, 20–39 years n = 4078, 40–59 years n = 4788, 60–79 years n = 3221, 80+ years n = 1332. After the peak (March 22, 2020), incidence declined in older age groups and increased among age 0–19 and 20–39 age groups from 20% to 40% of total cases by April 19 and 50% by May 3. During this time testing expanded with more testing among older age groups and less testing among younger age groups while case positivity shifted young. Percent positive cases age 0-19/20-39 years through August 2020 increased to a consistent average of 60% [age 0–19 increased to 19% (N = 10257), age 20–39 increased to 42% (N = 30215)].

Conclusions An increased sustained proportion of COVID-19 incidence is present among children (age 0–19) and young adults (age 20–39) indicating an elevated role in disease spread during the epidemic creating a possible reservoir of disease with spillover risk to more vulnerable older persons and those with comorbid conditions. Media savvy age-appropriate messaging to enhance mitigation compliance among less vulnerable, more mobile and lower priority vaccination age groups will be a continued necessity and priority to reduce overall population incidence.