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COVID-19: Epidemiology

by Sean Elliott, MD

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    00:01 COVID-19 Epidemiology.

    00:04 As I think most people know by now the first case of SARS-Coronavirus II infection or COVID-19, was found in November 2019 in Wuhan province in China, with an outbreak developing shortly thereafter, in the following month.

    00:18 As of March, 11, 2020, the World Health Organization, declared a pandemic with incredible spread throughout the world.

    00:26 And today, there are reported COVID-19 cases everywhere, every continent, every country, 220 countries plus.

    00:35 The rates of severe, critical and fatal cases of course depend, upon the country and its age demographics, its age groups and its rates of access to healthcare delivery, but children and adolescents, who in other epidemics and pandemics account, for a huge number of the cases account for, just, I know it's a large percentage, but just 13% of current COVID-19 cases in the United States.

    01:02 Globally, these are all patients, there are over 190 million cases, as of July of 2021, and over 4 million deaths.

    01:12 This again, involves largely older individuals, as we'll see in this session.

    01:18 There are, in addition to the initial caseloads, there are thousands of genetic mutations of the virus itself, causing mutant variants, which exist, despite the incredible number of variants, there are four that actually are currently of global concern.

    01:37 And they are the B.1.1.7 or the Alpha variant, initially described in the United Kingdom, the B.1.351 the Beta variant, initially described in South Africa, the B.1.617.2 sub variant two or the Delta variant this is the big one currently and initially described in India and the P.1 or the Gamma variant initially described in Brazil.

    02:02 These four variants are variants of concern and what does that mean? It means that the viral mutant or the viral variant, has at least one of the following, so, a higher infection rate and those four variants of concern that I've just listed, all have infectivity rates 30% to 60% greater than the initial strain of SARS-Coronavirus II, a variant of concern will cause more severe cases.

    02:29 Now that may be to increase virulence from the virus itself or it may be, that because it is far more infectious, it is infecting far higher numbers of at-risk individuals, with clinical comorbidities.

    02:43 A variant of concern, will have reduction in neutralization by antibodies, either from previous infection or by currently available vaccination and currently available treatments will have reduced effectiveness.

    02:58 Also, and perhaps because of the reduced effectiveness of treatments, there is also a reduced effectiveness of detection.

    03:05 So, clinical testing strategies may fail to pick up a variant of concern, thus, we may not know what we don't know.

    03:13 There may be higher numbers that are currently being reported from an area or a part of the world.

    03:18 Now, a variant of interest is sort of the precursor to a variant of concern, a meaning that this variant is potentially serious, but not yet confirmed to have the degree of infectivity as seen with the variant of concern and it may be of interest or potentially serious, because it has the genetic markers, that have been seen in an existing variant of concern.

    03:41 Of worst concern, is a variant of high consequence and that this is a variant that in addition to having higher infectivity, higher virulence, higher severity, reduced effectiveness with treatment et cetera, that it has already eclipsed all the countermeasures, that we currently have available in medical science and that whatever we do, has significantly reduced effectiveness.

    04:06 So, reduced diagnostics, reduced vaccine effectivity, reduced therapeutic interventions et cetera and knock-on wood, there are no current variants that meet this this criteria, but, the Delta variant the one from India, is being watched closely as it has this potential to eclipse, our currently available medical interventions.

    04:32 So, what are the impacts of the variants so again the B.1.1.7, the Alpha variant initially from the United Kingdom, known to have increased transmissibility, anywhere from 30% to 50%, possibly increase severity, however, protection from currently available vaccines, has been good.

    04:52 The South African variant the B.1.351 or the Beta variant, similarly increased transmissibility, similar potential of higher severity.

    05:05 The vaccines currently available appear to be, somewhat less protective and especially among younger age groups and so there is concern that this variant, may preferentially attack, school children and young adults, in countries in which it gains a foothold.

    05:20 The Brazil variant the P.1 or the Gamma variant, again, anywhere from 20% to 30% more infectious, increased severity possible, however, the current available vaccines, likely have good protection against it.

    05:34 Fortunately, its numbers have been low in other parts of the world, other than the Central and South Americas and so, it has not yet been formally tested aggressively, in its response to the vaccine.

    05:48 And then the Delta variant India B.1.617.2 sub variant two, why do I say sub variant? Because there are at least three variants, 1, 2, 3, of the B.1.617.

    06:01 It is the subvariant two however which is known to be far more transmissible, than the others.

    06:06 So, up to 60% increase in effectivity, possibly to even probably increased severity, most vaccines continue to have likely protection against it, again, with some concern that those who have decreased vaccine response, such as somebody who's immunocompromised, may not be as well protected against the delta variant.

    06:28 So, now, let's look at risks or rates I should say, for COVID-19 infection hospitalization and death by age group and this is where the severity the pandemic really starts to be highlighted.

    06:42 So, in these tables, the rates are all compared to the 5 to 17-year-old age group, as a reference group, why is this one chosen? Likely because this age group typically is the most infectious, although the least affected by other epidemics, such as influenza.

    07:00 So, if you look at cases initially, and the age groups as you see across the top, are from 0 to 4 years, 5 to 17 is our reference group, 18 to 19 years, 30 to 39 years, 40 to 49, you get the picture.

    07:14 So, as we look at cases the young children 0 to 4, are less than one times, as likely to have cases, as the 5 to 17-year-old reference group.

    07:25 Whereas, most of the other categories, with the exception of 75 to 84 years old, are twice as likely to have an actual COVID-19 case.

    07:35 Why the drop in in case rate for the 75 to 84? Unclear, this this may just simply be from recording cases and or impact of other comorbidities.

    07:46 Rates or risk for of hospitalization.

    07:49 Young children 0 to 4, two times as likely as the older children adolescent reference group, but if you look then at the other following age groups, the rates just keep going higher and higher and higher to where as, the 85 plus years old individuals, 95 times as likely to be hospitalized with COVID-19, as our reference group of young children and adolescents.

    08:12 Death, here again, significant and horrifying rates starting with even young adults 18 to 29, who are 10 times as likely to die, as the child to adolescent, but looking all the way to the right the 85 plus years old, 8,700 times as likely to die with COVID-19, as the young child to adolescent.

    08:35 So, this is terrible of course, and I think as we'll get to in just a little bit, there are there are reasons for this, but just in looking at the chart a potential sample interpretation, compared to those who are ages 5 to 17 years old, the rate of death is 45 times higher in the 30 to 39 years old age group and 8,700 times higher in the 85 and older years age group.

    09:01 So, what is the risk for mortality and serous disease, if you look from age 5 to 17 our reference group, is 45 times higher in the 30 to 39 and another 8,700 times higher, in those 85 and older.

    09:15 So, this disease is absolutely targeting individuals who are age 65 and up, in fact, 80%, of the deaths so far to date in this global pandemic, have been individuals who are older than 65, why is that? And here's where it really it comes down to.

    09:33 The major risk for death had to do with comorbidities, in addition to age and as one ages one is more likely to have these comorbidities and you see them listed there.

    09:43 Cancer, cardiovascular, cerebrovascular disease, so those who already have strokes, chronic kidney disease, chronic obstructive pulmonary disease (COPD), those with diabetes mellitus, especially those who are insulin dependent diabetes mellitus, anyone with a serious heart condition and including hypertension, which is uncontrolled, obesity a BMI greater than 30, is an absolute indicator of higher risk of mortality, as well as hospitalization with COVID-19 and then current or recent pregnancy, largely due to the transient immunosuppression that a pregnant mother experiences.

    10:20 And then those who are smokers, likely because this risk co-migrates with several those other heart/coronary respiratory diseases you see listed there.

    10:31 So, this is a big deal, this virus is a killer as I think we all know, and as we continue to understand more about physiologic reasons for that, I think we'll realize that it has to do with its targeting and what structures it targets, as it goes into causing hospitalization and death.


    About the Lecture

    The lecture COVID-19: Epidemiology by Sean Elliott, MD is from the course Coronavirus.


    Included Quiz Questions

    1. More contagious than the original virus
    2. Lower fatality rate
    3. Lack of effectiveness of current vaccines
    4. Causes more respiratory failure
    5. Transmissible from asymptomatic individuals
    1. United Kingdom
    2. South Africa
    3. India
    4. Brazil
    5. China
    1. 85 and up
    2. 50 to 64
    3. 65 to 74
    4. 75 to 84
    5. 40 to 49
    1. 45 times higher
    2. 10 times higher
    3. 25 times higher
    4. 100 times higher
    5. 300 times higher
    1. ...people over age 65.
    2. ...children under age 5.
    3. ...people with diabetes.
    4. ...immunocompromised individuals.
    5. ...people over age 50.

    Author of lecture COVID-19: Epidemiology

     Sean Elliott, MD

    Sean Elliott, MD


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