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Herd immunity occurs when a high enough percentage of the population becomes immune that a virus cannot be easily transmitted from person-to-person. Immunity is typically achieved through having the disease or through vaccinations. With regard to COVID-19, it has been estimated that to achieve herd immunity 60-80% of the population may need to be immune. Since there currently is no vaccine, the only way to achieve immunity now is to be infected; however, it is not known how long this natural immunity lasts. Additionally, long-lasting effects of COVID-19 have been reported, which would be a problem with achieving immunity via being infected. Learn more in our epi mini-lesson.
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On February 11, 2020 the World Health Organization announced an official name for the disease that is causing the 2019 novel coronavirus outbreak, first identified in Wuhan China. The new name of this disease is coronavirus disease 2019, abbreviated as COVID-19. In COVID-19, ‘CO’ stands for ‘corona,’ ‘VI’ for ‘virus,’ and ‘D’ for disease. Formerly, this disease was referred to as “2019 novel coronavirus” or “2019-nCoV”. The name of the virus that causes COVID-19 is the SARS-CoV-2 virus. There are many types of human coronaviruses including some that commonly cause mild upper-respiratory tract illnesses and other more deadly coronaviruses including SARS-CoV and MERS-CoV. SARS stands for ‘severe acute respiratory syndrome’. COVID-19 is a new disease, caused by a novel (or new) coronavirus that has not previously been seen in humans.
Community spread means people have been infected with the virus in a certain geographical area, including some who are not sure how or where they became infected. For larger South Dakota counties, the South Dakota Department of Health determines the level of community spread based on the number of new cases per week over the previous two weeks per 100,000 population.
Fully recovered clinically means that there are no more lingering effects. In terms of the Department of Health COVID-19 dashboard, recovered means that the infected person no longer needs to be isolated. Learn more in our epi mini-lesson.
Community mitigation is a set of actions that people and communities can take to slow the spread of infectious diseases like COVID-19. The goal of community mitigation in areas with local COVID-19 transmission is to slow its spread and to protect all individuals, especially those at increased risk for severe illness, while minimizing the negative impacts of these strategies.
The case count is the number of confirmed and probable cases of COVID-19 that have been reported in the county. A confirmed case is a person that has been diagnosed using a RT-PCR test (an accurate laboratory method). A probable case is a person that has been diagnosed using an antigen test for the SARS-CoV-2 virus that causes COVID-19 (not as accurate as RT-PCR, but a more rapid test). The South Dakota Department of Health website gives information on both confirmed and probable cases.
A running average smooths out short-term fluctuations in data and highlights longer-term trends. An example of fluctuations in the data that occur are on weekends when data are less likely to be reported and when there are smaller numbers. The intent of taking a running average is to give a more representative view of what is going on with new cases or identify trends over time. Learn more in our epi mini-lesson.
The case fatality rate is the percent of individuals who tested positive for COVID-19 that died from COVID-19. Since it is a percentage, you have to define a numerator and a denominator. The numerator is the number of people who died from COVID-19. Because new cases are being diagnosed daily, the denominator includes only people who have recovered per CDC definition (active cases could still die) as well as those who died. Learn more in our epi mini-lesson.
Cause of death is determined by either the attending licensed physician, physician assistant, or certified nurse practitioner. If there was no attending health professional, the county coroner is responsible. If there is no coroner, the local registrar prepares the death certificate based on statements of relatives or other individuals who know the facts. All these individuals must have training in the registering of death certificates. Learn more in our epi mini-lesson.
Misinformation is false information that is spread, regardless of intent to mislead. Learn more in our epi mini-lesson.