An epidemic curve has a relatively predictable upslope and once the peak is reached, the back slope can also be predicted. We have robust data from the outbreaks in China and Italy, that shows the backside of the mortality curve declines slowly, with deaths persisting for months. Assuming we have just crested in deaths at 70k, it is possible that we lose another 70,000 people over the next 6 weeks as we come off that peak. That's what's going to happen with a lockdown.
As states reopen, and we give the virus more fuel, all bets are off. I understand the reasons for reopening the economy, but I've said before, if you don't solve the biology, the economy won't recover.
There are very few states that have demonstrated a sustained decline in numbers of new infections. Indeed, as of May 3rd the majority are still increasing and reopening. As a simple example of the USA trend, when you take out the data from New York and just look at the rest of the USA, daily case numbers are increasing. Bottom line: the only reason the total USA new case numbers look flat right now is because the New York City epidemic was so large and now it is being contained.
So throughout most of the country we are going to add fuel to the viral fire by reopening. It's going to happen if I like it or not, so my goal here is to try to guide you away from situations of high risk.
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In order to get infected you need to get exposed to an infectious dose of the virus; based on infectious dose studies with
MERS and
SARS (and this one), some estimate that as
few as 1000 SARS-CoV2 viral particles are needed for an infection to take hold. Please note, this still needs to be determined experimentally, but we can use that number to demonstrate how infection can occur. Infection could occur, through 1000 viral particles you receive in one breath or from one eye-rub, or 100 viral particles inhaled with each breath over 10 breaths, or 10 viral particles with 100 breaths. Each of these situations can lead to an infection.
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Treat public bathrooms with extra caution (surface and air), until we know more about the risk.
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A single cough releases about 3,000 droplets and droplets travels at 50 miles per hour. Most droplets are large, and fall quickly (gravity), but many do stay in the air and can travel across a room in a few seconds
A single sneeze releases about 30,000 droplets, with droplets traveling at up to
200 miles per hour. Most droplets are small and travel great distances (easily across a room).
If a person is infected, the droplets in a single cough or sneeze may contain as many as 200,000,000 (two hundred million) virus particles which can all be dispersed into the environment around them.
A single breath releases 50 - 5000 droplets. Most of these droplets are low velocity and fall to the ground quickly. There are even fewer droplets released through nose-breathing. Importantly, due to the lack of exhalation force with a breath, viral particles from the lower respiratory areas are not expelled.
Unlike sneezing and coughing which release huge amounts of viral material, the respiratory droplets released from breathing only contain low levels of virus. We don't have a number for SARS-CoV2 yet, but we can use influenza as a guide.
We know that a person infected with influenza releases about 3 - 20 virus RNA copies per minute of breathing.
Remember the formula: Successful Infection = Exposure to Virus x Time
If a person coughs or sneezes, those 200,000,000 viral particles go everywhere...
But even if that cough or sneeze was not directed at you, some infected droplets--the smallest of small--can hang in the air for a few minute...
But with general breathing, 20 copies per minute into the environment, even if every virus ended up in your lungs, you would need 1000 copies divided by 20 copies per minute = 50 minutes.
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The exposure to virus x time formula is the basis of contact tracing. Anyone you spend greater than 10 minutes with in a face-to-face situation is potentially infected.
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Symptomatic people are not the only way the virus is shed.
We know that at least 44% of all infections--and the majority of community-acquired transmissions--occur from people without any symptoms (asymptomatic or pre-symptomatic people)
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Just to see how simple infection-chains can be,
this is a real story from Chicago. The name is fake. Bob was infected but didn't know. Bob shared a takeout meal, served from common serving dishes, with 2 family members. The dinner lasted 3 hours. The next day, Bob attended a funeral, hugging family members and others in attendance to express condolences. Within 4 days, both family members who shared the meal are sick. A third family member, who hugged Bob at the funeral became sick. But Bob wasn't done. Bob attended a birthday party with 9 other people. They hugged and shared food at the 3 hour party. Seven of those people became ill. Over the next few days Bob became sick, he was hospitalized, ventilated, and died.
But Bob's legacy lived on. Three of the people Bob infected at the birthday went to church, where they sang, passed the tithing dish etc. Members of that church became sick. In all, Bob was directly responsible for infecting 16 people between the ages of 5 and 86. Three of those 16 died.
The spread of the virus within the household and back out into the community through funerals, birthdays, and church gatherings is believed to be responsible for the broader transmission of COVID-19 in Chicago. (
ref)