Estimating the Instantaneous Asymptomatic Proportion With a Simple Approach: Exemplified With the Publicly Available COVID-19 Surveillance Data in Hong Kong

Background: The asymptomatic proportion is a critical epidemiological characteristic that modulates the pandemic potential of emerging respiratory virus, which may vary depending on the nature of the disease source, population characteristics, source–host interaction, and environmental factors.Methods: We developed a simple likelihood-based framework to estimate the instantaneous asymptomatic proportion of infectious diseases. Taking the COVID-19 epidemics in Hong Kong as a case study, we applied the estimation framework to estimate the reported asymptomatic proportion (rAP) using the publicly available surveillance data. We divided the time series of daily cases into four stages of epidemics in Hong Kong by examining the persistency of the epidemic and compared the rAPs of imported cases and local cases at different stages.Results: As of July 31, 2020, there were two intermittent epidemics in Hong Kong. The first one was dominated by imported cases, accounting for 63.2% of the total cases, and the second one was dominated by local cases, accounting for 86.5% of the total cases. The rAP was estimated at 23.1% (95% CI: 10.8–39.7%) from January 23 to July 31, and the rAPs were estimated at 22.6% (95% CI: 11.1–38.9%) among local cases and 38.7% (95% CI: 9.0–72.0%) among imported cases. Our results showed that the rAPs of local cases were not significantly different between the two epidemics, but increased gradually during the first epidemic period. In contrast, the rAPs of imported cases in the latter epidemic period were significantly higher than that in the previous epidemic period.Conclusion: Hong Kong has a high rAP of imported COVID-19 cases and should continue to strengthen the detection and isolation of imported individuals to prevent the resurgence of the disease.

One Possible Reinfection with SARS-CoV-2 Validated by 205-days Interval of Re-detection in Sapporo City, Japan

Since SARS-CoV-2 has spread all over the world, one of the key questions is how long immunity works for protecting hosts from infection. However, it was difficult to distinguish reinfection from re-detected positive cases caused by other reasons. We confirmed 23 re-detected positive cases in Sapporo City in 2020, and among them, the case with 205-days interval from initial onset to the second confirmation date was found. We calculated the probability of observing more than one case with over d-days interval of re-detection, pobs, to find out whether the case with 205-days interval had the similar epidemiological characteristic with others or not. We found that 5th percentile and its 95% confidence interval of pobs was 118 (45, 216) for Sapporo City data and 92 (86, 98) for KCDC data. This result indirectly suggested the case with 205-days interval was reinfection.

Countermeasures against the introduction and spread of coronavirus infection COVID-19 in medical organizations

The article presents a brief epidemiological characteristic of a new coronavirus infection. The risks of infection of medical workers and measures to counter the drift and spread of COVID-19 in medical organizations are considered.

An Epidemiological Characteristic of the COVID-19 Among Children

A novel Coronavirus disease 2019 (COVID-19) is an infectious disease caused by SARS coronavirus 2 (SARS-CoV-2), which affects the respiratory system of human beings. Until now, numbers of COVID-19 cases have been reported among children; in China, less than 2.4% of the total cases occurred in those aged under 19 years old. SARS-CoV-2 transmission in children mostly occurs through contact with adult patients, primarily through exposure in the home. This article discusses the epidemiological features of COVID‐19 in children.

Model of Prophylactic Efficiency of Influenza Virus Vaccine Corrected to the Antigenic Distance Hypothesis

The aim of the study is to find a quantitative relationship between antigenic distances (AD) and vaccination effectiveness (VE) and investigate the response of VE to changes in AD.Material and methods. Through the epidemiological data of three influenza seasons in Canada, interpreted within the framework of the antigenic distance hypothesis (ADH), the introduction of the correction factor into the model for estimating VE was substantiated considering the antigenic relationship between the previous season vaccine (V1), the current season vaccine (V2) and the circulating epidemic strain (e).Results. A quantitative relationship between VE and AD was found, reproducing the results of epidemiological observation of two groups of people: vaccinated in the previous and current seasons (V1+V2) and vaccinated only in the current season (0+V2). The difference in the response of VE to different indicators of AD was found and allowing to use only one significant indicator.Conclusion. Тhe model proposed relates the microbiological indicators AD with epidemiological characteristic of VE. The model extends the analysis, allowing to use it as an assessment tool for the expected changes in vaccine effectiveness in various settings of the ADH hypothesis experiment.