Abstract
Objectives
Epidemiological investigations and mathematical models have revealed that the rapid diffusion of Covid-19 can mostly be attributed to undetected infective individuals who continue to circulate and spread the disease: finding their number would be of great importance in the control of the epidemic.
Methods
The dynamics of an infection can be described by the SIR model, which divides the population into susceptible
, infective
, and removed
subjects. In particular, we exploited the Kermack-McKendrick epidemic model, which can be applied when the population is much larger than the fraction of infected subjects.
Results
We proved that the fraction of undetected infectives, compared to the total number of infected subjects, is given by
, where
is the basic reproduction number. The mean value
for the Covid-19 epidemic in three Italian regions yielded a percentage of undetected infectives of 52.4% (52.2%–52.6%) compared to the total number of infectives.
Conclusions
Our results, straightforwardly obtained from the SIR model, highlight the role of undetected carriers in the transmission and spread of the SARS-CoV-2 infection. Such evidence strongly recommends careful monitoring of the infective population and ongoing adjustment of preventive measures for disease control until a vaccine becomes available for most of the population.
【저자키워드】 COVID-19, SARS-CoV-2, Epidemiology, Undetected cases, SIR model, 【초록키워드】 Vaccine, Infection, Transmission, Spread, Epidemic, basic reproduction number, disease, Epidemiological investigation, Evidence, preventive measure, individual, mean value, fraction, diffusion, carrier, infective, objective, susceptible, the epidemic, highlight, Result, described, subjects, number of infected, mathematical, Italian region, the SARS-CoV-2, 【제목키워드】 pandemic, infective,