[This is an email I sent a couple of friends who requested my take on things]
Lots of links down below.
If you’re going to read one, read this one (it’s also down below):
If two, add this one:
Here’s the short version:
COVID-19 is more infectious and more deadly than a typical (or even a serious) seasonal flu. Estimates of total infections in the US range from 65 to 230 million without attempts at mitigation, with accompanying death tolls of 600K to 9 million.
The big worry is overwhelming our hospital capacity so that serious cases cannot be supported until recovery.
Social distancing, infection avoidance (hand washing, sanitizing, avoiding touching the face, etc.) are our only current weapons to mitigate spread of the disease.
Forgot to add: when you look at numbers of deaths, those infections happened at least 3 weeks ago (possibly 5). So we are looking into the past. Depending upon doubling rate, the current expected deaths from infections happening down will be between 8-64 times larger if the doubling rate is 6 days and 16-1000 times larger if the doubling rate is 3 days.
Here’s the long version:
The Disease:
While numbers continue to come in, there appears to be no question that SARS-CoV-2 (the virus which causes the disease COVID-19) is both more infectious and more deadly than a typical seasonal flu. Depending upon the research the doubling rate of COVID-19 appears to be somewhere in the 3-6 day range, and the death rate looks to be a minimum of about 1% (with full treatment options available) and a maximum of maybe 4% (if the healthcare system is overloaded and treatment options become more limited).
Incubation period can be up to 14 days and a full course of disease is 20-30 days.
The Spread:
Up to 80% of cases are thought to be mild, many of them completely asymptomatic. There is no symptom based diagnostic that can differentiate between COVID-19 and a bad cold or the flu. Up to 15% are “serious” requiring at least medical monitoring if not hospitalization, and around 5% are “critical” requiring significant medical intervention (at least oxygen, possibly ventilation) meaning the use of ICU or CCU beds.
Some research indicates that people infected with SARS-CoV-2 shed virus days before they become symptomatic (if they ever do) and for some time after they “recover” if their cases are mild.
Transmission is not yet known to be aerosolized, but appears primarily droplet-based. Basically, people with the disease shed virus through natural secretions including mucous and feces. A sneeze projects infected droplets for at least several feet, and those droplets stay on surfaces for at least hours and possibly days. When a sick person touches their face they are likely to get traces of mucous on their hands which they then deposit on surfaces they touch, including tables, door handles, keyboards and screens, and so on.
Estimates of infection rates in the general populace over the course of the outbreak range from 20%-70%. The time frame is not usually specified but we are most likely talking about under a year, depending upon mitigation strategies.
In the US, that means between 65 million and 230 million people will be infected. 65 million is roughly the number of infections in the US during a bad seasonal flu year.
At 1% mortality, that’s 650K - 2.3 million deaths in the US. At 4%, it’s 2.5 million to 9 million.
Treatments and Vaccines:
A vaccine will take at least a year to get through safety testing and trials. Initial testing has already begun on at least one vaccine but first attempts don’t always work. A safe assumption is that a vaccine is at least a year and a half out, possibly two years.
For now, treatment is strictly supportive, meaning that serious and critical cases get put to bed and watched. As their breathing is reduced, first oxygen and later mechanical ventilation are used to keep the patient alive while the disease runs its course. In some cases, secondary infections will be treated with antibiotics.
Mitigation:
Without a vaccine, the only mitigation available is limiting the spread of the disease. Epidemiologists use R0 (“R-nought”) as a measure of replication of a disease in a population. If R0 is 1, each infected person gives the disease to one other individual (on average) and the number of cases in the population is stable over the long term. If R0 is below 1, the number of cases falls over time. If R0 is above 1, the number of cases increases over time.
The only weapon we have against this disease spreading is reducing R0. The easiest way to do that is to reduce the number of contacts between infected people and uninfected people. Unfortunately, infected people don’t have a giant sign on them saying “COVID-19! Stay Away”. Since many cases of COVID-19 are asymptomatic, and because patients shed virus before being symptomatic, we cannot isolate patients nor can we selectively avoid them.
The solution is to reduct contacts with _everyone_. “Social distancing” means drastically reducing the number of direct in-person interactions you have with people. Staying home. Staying at least six feet away from people when you do go out.
Alongside reducing contacts goes reducing the chance of infection. Since SARS-CoV-2 must enter the body to infect you and you generally pick it up on your hands, hand-washing often (for at least 20 seconds) is a useful mechanism to reduce infection rates. Where hand washing is not possible, hand sanitizer (at least 60% alcohol) is better than nothing. Avoiding touching your face with possibly infected hands reduces infections through the mouth, nose, and eyes.
Effects of Mitigation:
Modeling shows (and the experience of Hubei Province in China confirms) that radical contact reduction (“lockdown”) is effective in slowing or even stopping the spread of the virus.
But the level of contact reduction has to be big. At least 75% on an individual basis. That’s why all the recommendations to stay at home (“shelter in place”), close business, avoid crowds, etc.
Sources
Here’s where I start every day. During the early stages, these various surveillance sites all agreed on the numbers. Now they don’t, but they generally end up syncing up at least once or twice a day as they troll for numbers and update:
This is automated graphing of various statistics about the outbreak: