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Journal of the Royal Society Interface ; 19(195), 2022.
Article in English | Web of Science | ID: covidwho-2087951


Some asymptomatic individuals carrying SARS-CoV-2 can transmit the virus and contribute to outbreaks of COVID-19. Here, we use detailed surveillance data gathered during COVID-19 resurgences in six cities of China at the beginning of 2021 to investigate the relationship between asymptomatic proportion and age. Epidemiological data obtained before mass vaccination provide valuable insights into the nature of pathogenicity of SARS-CoV-2. The data were collected by multiple rounds of city-wide PCR testing with contact tracing, where each patient was monitored for symptoms through the whole course of infection. The clinical endpoint (asymptomatic or symptomatic) for each patient was recorded (the pre-symptomatic patients were classified as symptomatic). We find that the proportion of infections that are asymptomatic declines with age (coefficient = -0.006, 95% CI: -0.008 to -0.003, p < 0.01), falling from 42% (95% CI: 6-78%) in age group 0-9 years to 11% (95% CI: 0-25%) in age group greater than 60 years. Using an age-stratified compartment model, we show that this age-dependent asymptomatic pattern, together with the distribution of cases by age, can explain most of the reported variation in asymptomatic proportions among cities. Our analysis suggests that SARS-CoV-2 surveillance strategies should take account of the variation in asymptomatic proportion with age.

Working Paper Series National Bureau of Economic Research ; 51, 2022.
Article in English | GIM | ID: covidwho-2080107


Safe and effective vaccines have vastly reduced the lethality of the COVID-19 pandemic worldwide, but disparities exist in vaccine take-up. Although the out-of-pocket price is set to zero in the U.S., time (information gathering, signing up, transportation and waiting) and misinformation costs still apply. To understand the extent to which geographic access impacts COVID-19 vaccination take-up rates and COVID-19 health outcomes, we leverage exogenous, pre-existing variation in locations of retail pharmacies participating the U.S. federal government's vaccine distribution program through which over 40% of US vaccine doses were administered. We use unique data on nearly all COVID-19 vaccine administrations in 2021. We find that the presence of a participating retail pharmacy vaccination site in a county leads to an approximately 26% increase in the per-capita number of doses administered, possibly indicating that proximity and familiarity play a substantial role in vaccine take-up decisions. Increases in county-level per capita participating retail pharmacies lead to an increase in COVID-19 vaccination rates and a decline in the number of new COVID-19 cases, hospitalizations, and deaths, with substantial heterogeneity based on county rurality, political leanings, income, and race composition. The relationship we estimate suggests that averting one COVID-19 case, hospitalization, and death requires approximately 25, 200, and 1,500 county-level vaccine total doses, respectively. These results imply a 9,500% to 22,500% economic return on the full costs of COVID-19 vaccination. Overall, our findings add to understanding vaccine take-up decisions for the design of COVID era and other public health interventions.

PLoS Global Public Health ; 2(1), 2022.
Article in English | CAB Abstracts | ID: covidwho-1854928


Symptomatic testing programmes are crucial to the COVID-19 pandemic response. We sought to examine United Kingdom (UK) testing rates amongst individuals with test-qualifying symptoms, and factors associated with not testing. We analysed a cohort of untested symptomatic app users (N = 1,237), nested in the Zoe COVID Symptom Study (Zoe, N = 4,394,948);and symptomatic respondents who wanted, but did not have a test (N = 1,956), drawn from a University of Maryland survey administered to Facebook users (The Global COVID-19 Trends and Impact Survey [CTIS], N = 775,746). The proportion tested among individuals with incident test-qualifying symptoms rose from ~20% to ~75% from April to December 2020 in Zoe. Testing was lower with one vs more symptoms (72.9% vs 84.6% p<0.001), or short vs long symptom duration (69.9% vs 85.4% p<0.001). 40.4% of survey respondents did not identify all three test-qualifying symptoms. Symptom identification decreased for every decade older (OR = 0.908 [95% CI 0.883-0.933]). Amongst symptomatic UMD-CTIS respondents who wanted but did not have a test, not knowing where to go was the most cited factor (32.4%);this increased for each decade older (OR = 1.207 [1.129-1.292]) and for every 4-years fewer in education (OR = 0.685 [0.599-0.783]). Despite current UK messaging on COVID-19 testing, there is a knowledge gap about when and where to test, and this may be contributing to the ~25% testing gap. Risk factors, including older age and less education, highlight potential opportunities to tailor public health messages. The testing gap may be ever larger in countries that do not have extensive, free testing, as the UK does.

Mmwr-Morbidity and Mortality Weekly Report ; 71(13):489-494, 2022.
Article in English | Web of Science | ID: covidwho-1798160
International Journal of Infectious Diseases ; 116:S50-S50, 2022.
Article in English | PMC | ID: covidwho-1720036