Flu pandemics for the last 250 years have had two peaks. Weather does not appear to effect their severity. Original assessment of the basic reproductive number, i.e., R0, of COVID-19 was ~2.5, with the Wikipedia entry on herd immunity citing a possibility as low as 1.4.
But, R0 of COVID-19 has been reassessed, and it is now thought to be ~5.7. This is important because at 1.4, it has low transmissiblity. Only 29% of people need to have had the disease and recovered to break chains of transmission. As R0 increases, so does the percent of the population required for herd immunity, i.e., R0 of 4, requires 75% immunity, 5 is 80%, 6 is 83% and 7 is 86%. As a point of comparison, Spanish Flu had an R0 of ~2.
Without a vaccine or effective treatment that can be produced at scale, you want to reduce the infection rate to get to herd immunity at a slower pace. By reducing the burden on health care systems, you also reduce the number of people that die because they cannot get modern medical care. As time is shortened, less people get care and more people die. It’s the idea behind “flatten the curve”. More time also means more time to develop some kind of treatment or a vaccine to get to herd immunity without so many dying or even getting the illness.
The important questions right now are: (1) How many people have been infected, since some were either asymptomatic or had mild symptoms? (2) Of people infected, how many died?
The initial results from the first “sero-surveys”, that is blood tests taken from a representative sample of a population looking for antibodies that indicate a person had COVID-19, indicate herd immunity is ~15% for a population that have been through their first peak and the death rate from COVID-19 when hospital systems are not overwhelmed is ~0.4%.
So, why is the above important? It means to get to herd immunity, something like 82% of people will have to get infected and of those that get infected, 0.4% will die. Then, we can calculate:
Population * Percentage of People For Herd Immunity * Death Rate = Deaths
In the case of the United States, that works out to something like:
341,000,000 * .82 * .004 = 1,118,480 U.S. deaths
If you look at the entire world and assume the fatality rate doubles on average because of how much of the world does not have access to healthcare, you get:
7,800,000,000 * .0.82 * .008 = 51,168,000 worldwide deaths
And with this knowledge in hand, when the yahoos in government tell you that “their model” indicates that only 60,000 people will die in the U.S., that things can go back to normal after a few weeks of “shelter-in-place” and May is a good time to restart the economy, you’ll know that you are being bullshitted.
The reality is that May will be the down slope of the first peak. The crisis will continue through the summer at a lower level and likely have a second peak in September/October. Given how badly it is being handled in the United States, we will reach herd immunity faster, with all the additional fatalities that entails.
Wait for the serological tests in the United States to look like the German ones that have already been done, and hopefully, in a sane world, a “pivot” back to something like the grim reality of what we are dealing with here by what passes as the U.S. federal “government”.
“Some limited data support a potential waning of cases in warmer and more humid seasons, yet none are without major limitations. Given that countries currently in “summer” climates, such as Australia and Iran, are experiencing rapid virus spread, a decrease in cases with increases in humidity and temperature elsewhere should not be assumed. Given the lack of immunity to SARS-CoV-2 across the world, if there is an effect of temperature and humidity on transmission, it may not be as apparent as with other respiratory viruses for which there is at least some pre-existing partial immunity. It is useful to note that pandemic influenza strains have not exhibited the typical seasonal pattern of endemic/epidemic strains. There have been 10 influenza pandemics in the past 250-plus years – two started in the northern hemisphere winter, three in the spring, two in the summer and three in the fall. All had a peak second wave approximately six months after emergence of the virus in the human population, regardless of when the initial introduction occurred.”
-National Academies of Sciences, Engineering, and Medicine. 2020. Rapid Expert Consultation on SARS-CoV-2 Survival in Relation to Temperature and Humidity and Potential for Seasonality for the COVID-19 Pandemic (April 7, 2020). Washington, DC: The National Academies Press. https://doi.org/10.17226/25771.
“”Initial estimates of the early dynamics of the outbreak in Wuhan, China, suggested a doubling time of the number of infected persons of 6–7 days and a basic reproductive number (R0) of 2.2–2.7. We collected extensive individual case reports across China and estimated key epidemiologic parameters, including the incubation period. We then designed 2 mathematical modeling approaches to infer the outbreak dynamics in Wuhan by using high-resolution domestic travel and infection data. Results show that the doubling time early in the epidemic in Wuhan was 2.3–3.3 days. Assuming a serial interval of 6–9 days, we calculated a median R0 value of 5.7 (95% CI 3.8–8.9).”
-Sanche S, Lin YT, Xu C, Romero-Severson E, Hengartner N, Ke R. High contagiousness and rapid spread of severe acute respiratory syndrome coronavirus 2. Emerg Infect Dis. 2020 Jul [April 11, 2020]. https://doi.org/10.3201/eid2607.200282
“From the result of their blood survey, the German team estimated the death rate in the municipality at 0.37% overall, a figure significantly lower than what’s shown on a dashboard maintained by Johns Hopkins, where the death rate in Germany among reported cases is 2%.
The authors explain that the difference in the calculations boils down to how many people are actually infected but haven’t been counted because they have mild or no symptoms.”
-Antonio Regalado, “Blood tests show 14% of people are now immune to covid-19 in one town in Germany.” MIT Technology Review. April 9, 2010.
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