Fig. 3 Scenario of epidemic development in Russia without restrictive measures. (Source: Covid-19-scenarios.org)
Increasing RO per unit significantly accelerates the process, if RO is 2, then the first infected person transmits the virus to two more people, then each of them transmits the virus to two more people and so on.
The index of the current COVID-19 coronavirus is about three. When the authorities restrict people’s contacts, the reproduction index decreases. Now all countries are trying to lower the reproduction rate below 1, hoping that at a slow rate of infection, restrictive measures can be eased (Fig. 2).
Reducing the reproduction index does not yet mean defeating the virus, but a low infection rate can be controlled through more economical measures - wearing masks, mass testing, tracking contacts and timely isolation of people with symptoms.
In order to model the coronavirus distribution, the University of Basel, Switzerland, developed an interactive model based on SEIR, where data (number of inhabitants, age structure, number of confirmed cases, etc.) are loaded automatically and RO is assumed to be 2.64-3.23.
If no restrictive measures were taken in Russia, according to this model, 1.3-1.36 million people would have died by the beginning of July, and the number of infected people at the peak of the epidemic would have been 14-22 million (Fig. 3).
If Russia eases the restrictions so that the number of people’s contacts will increase by 50%, the number of new infections may increase to 300,000 by May 31, 2020, and if nothing is changed or the number of contacts reduced by another 50%, the increase in infection will be almost invisible or not at all.
Based on mathematical modeling of COVID-19 epidemic development in Moscow, 5 scenarios of epidemic suppression and their possible consequences are presented [18]. The extended SEIR model [15], implemented as a public computer program, was used for modeling. 5 scenarios of the epidemic development are considered: 0 - zero scenario corresponds to the absence of protective measures, scenario A - a mild step to suppress the epidemic (closure of schools, universities, recommendations to elderly people not to leave home), scenario B and D - a complete knockdown, introduced in scenario B from the beginning of May, in scenario D - from the beginning of April 2020. In the O-variant, the number of deaths from COVID-19 in Moscow will exceed 100 thousand people, and the number of critical patients at the peak of the epidemic will exceed the capacity of the healthcare system by more than 10 times. Scenarios A and B do not radically reduce the number of deaths, and the number of critical patients at the peak of the epidemic will continue to far exceed the capacity of the health system. In addition, scenario B assumes that the epidemic will last for more than a year. Scenarios B and D can suppress the epidemic and significantly reduce the number of deaths (by 30 and 400 times, respectively). At the same time, as a result of these two scenarios, the population does not develop collective (group) immunity and the population will remain susceptible to repeated outbreaks of the epidemic.
Of the 50,000 Moscow citizens who voluntarily tested, antibodies to COVID-19 were found in 12.5-14% who are developing or have developed immunity to the coronavirus. Rather, the examined patients suffered from the disease in an asymptomatic or mild form, without contacting medical professionals. Based on the results of these studies, it can be assumed that those who acquired immunity during the asymptomatic course of COVID-19 in Moscow may be from 1,586,000 to 1,776,000 people, and the total number of infected, including officially registered (applied for medical care) patients then is from 175,000 to 1,946,000 people. Consequently, the proportion of those identified in medical organizations is only 8.69-9.64% of the total number of infected people.
During the last month, the growth of COVID-19 cases has been gradually decreasing: for example, during April 15-19, 2020, this figure was 14-15%, May 1-5, 2020 - 7-8%, and during the last week it dropped to 3% (21.05.2020).
In Sweden, the pandemic strategy included the following measures: 1. Do not interrupt business activities. 2. Don’t disrupt people’s daily lives. 3. Systematically move towards achieving collective immunity. Citizens were asked to observe social distancing precautions, but they were not required to do so and were not penalized for non-compliance. Two weeks ago, the health care system was on the verge of collapse, but the situation has improved and there has been no collapse. The number of infected people is still growing, and the death rate is higher than in other Scandinavian countries, but lower than in countries that have taken radical isolation measures. WHO now considers the Swedish model to be a possible model for countries waiting for a vaccine.
The effectiveness of COVID-19 restrictive measures to prevent the spread of infection has been studied comparatively in the states of Iowa (where they were not introduced) and Illinois, where these measures were introduced from March 21, 2020. [17]. In addition, the difference in the timing of closure of schools and businesses, population density and income levels were taken into account. The population density was higher in Iowa (114.2 people per square mile) than in Illinois (78.2 people). Summarized COVID-19 cases for 10,000 populations in both states were compared prior to the State of Illinois self-imposed isolator ordinance. After the decree, the incidence became higher in Iowa, decreased in Illinois. Within 10, 20, and 30 days of the Illinois Home Isolation Ordinance, the difference in COVID-19 cases was 0.51 per 10,000 residents (SE 0.09; 95%, CI is from 0.69 to 0.32; p<0.001; -1.15 per 10,000 population (SE 0.49; 95% CI is from -2.12 to -0.18; p=0.02) and -4.71 per 10,000 population (SE 1.99; 95% CI is from -8.64 to -0.78; p=0.02), respectively. These data demonstrate the effectiveness of home isolation to prevent the spread of COVID-19 even in selected regions of the country.
Medical organizations are known to be one of the frequent outbreak centers of infection. Often, when such a focal point arises in a general hospital, infected patients are transferred to other hospitals, creating a chain of infectious disease outbreaks, sometimes from infectious disease hospitals to non-infectious disease hospitals for surgical interventions. It is always a high risk of infection for patients and medical staff. It seems reasonable to introduce a surgeon to infectious diseases hospitals and to organize an operating room.
Conclusion. Analysis of the prevalence of the new coronavirus disease COVID-19 over a 4-month period from the initial ”emotional” assessment based on intensive indicators is gradually moving to a system of ”medical statistics”. The actual epidemiological situation, trends and prognosis can be most reliably assessed and determined based on relative morbidity and mortality rates.
It is necessary to distinguish such indicators as ”morbidity”, ”infection rate”, ”mortality” and ”lethality” according to the generally accepted postulates of medical statistics and epidemiology. Proper calculation of such indicators as morbidity (number of patients with COVID-19 per 1,000/100,000 of population), the rate of infection (or reproduction), allows to objectively assess the effectiveness of various restrictive measures in dynamics, helps to make decisions about the continuation or weakening of these activities, and for the health system - about the possibilities for the near future to cope with the upcoming flow of patients or make adjustments to strengthen their resources. Approximately the same importance of another indicator - mortality (the number of deaths per 100,000 population), although it characterizes the state, the level of health care system. Indicator - lethality (% deceased to the number of patients) - is primarily an assessment of the activities of medical organizations, medical workers, the level of medical knowledge, professionalism, the state of implementation of research results. Undoubtedly, the level of lethality is also connected with material and technical, medical equipment of medical organizations, opportunities of conversion of medical organizations into infectious diseases hospitals, organization of intensive care and resuscitation departments, providing the latter with equipment for non-invasive and invasive ventilation of the lungs, hemodialysis, efferent methods of treatment.
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