I had no idea that viruses, like poisons, are more dangerous at higher doses.
Higher exposure, higher danger.
Lower exposure, lower danger:
The importance of viral dose is being overlooked in discussions of the coronavirus….Small initial exposures tend to lead to mild or asymptomatic infections, while larger doses can be lethal.
From a policy perspective, we need to consider that not all exposures to the coronavirus may be the same. Stepping into an office building that once had someone with the coronavirus in it is not as dangerous as sitting next to that infected person for an hourlong train commute.
Both small and large amounts of virus can replicate within our cells and cause severe disease in vulnerable individuals such as the immunocompromised. In healthy people, however, immune systems respond as soon as they sense a virus growing inside. Recovery depends on which wins the race: viral spread or immune activation.
Virus experts know that viral dose affects illness severity. In the lab, mice receiving a low dose of virus clear it and recover, while the same virus at a higher dose kills them. Dose sensitivity has been observed for every common acute viral infection that has been studied in lab animals, including coronaviruses.
Humans also exhibit sensitivity to viral dose. Volunteers have allowed themselves to be exposed to low or high doses of relatively benign viruses causing colds or diarrhea. Those receiving the low doses have rarely developed visible signs of infection, while high doses have typically led to infections and more severe symptoms.
This strikes me as important, yet none of the COVID models seem to take viral dose into account in predicting the effects of lockdown.
Here’s the passage that gives me hope:
Low-dose infections can even engender immunity, protecting against high-dose exposures in the future. Before the invention of vaccines, doctors often intentionally infected healthy individuals with fluid from smallpox pustules. The resulting low-dose infections were unpleasant but generally survivable, and they prevented worse incidents of disease when those individuals were later exposed to smallpox in uncontrolled amounts.
Assuming that the low-dose principle holds true of COVID 19 (let’s hope) here’s my question:
Shouldn’t lockdown suppress high-dose exposure in favor of low-dose exposure?
And if so, will that save lives?
Here’s an example of what I mean.
A repair person came to our house yesterday morning. He was wearing a mask, and kept more than 6 feet away from the three of us.
If he has coronavirus, we three got a very low dose.
If we have coronavirus, he got a very low dose.
Under lockdown, people all over the country are having truncated and physically distant interactions like this, which ought to mean that people all over the country are receiving low-dose viral exposures to COVID 19 instead of the high-dose exposures they would have received without lockdown.
So: if low-dose exposure can produce immunity without severe disease in other viruses, might lockdown produce herd immunity with less illness and fewer deaths with COVID 19?
And shouldn’t models include low-dose exposure as a variable?
Is there another reason to flatten the curve?
The rationale for lockdown has been to flatten the curve, which simply means spreading severe illness and death out over time so hospitals aren’t overrun. In theory, flattening-the-curve results in fewer deaths, but only because those who can be saved are saved–not because fewer cases of serious illness occur in the first place. We suffer the same amount of illness, but more of us survive. That’s the idea.
But is that right?
If lockdown produces more low-dose exposures, might we also have fewer cases of serious illness in absolute numbers?
Might lockdown be able, potentially, to produce herd immunity with a lower number of deaths than we’d need to achieve herd immunity without?
St. Louis vs Philadelphia
I’ve been wondering about the now-famous cautionary tale of St. Louis versus Philadelphia during the Spanish Flu.
In 1918, the city of Philadelphia threw a parade that killed thousands of people. Ignoring warnings of influenza among soldiers preparing for World War I, the march to support the war effort drew 200,000 people who crammed together to watch the procession. Three days later, every bed in Philadelphia’s 31 hospitals was filled with sick and dying patients, infected by the Spanish flu.
By the end of the week, more than 4,500 were dead in an outbreak that would claim as many as 100 million people worldwide. By the time Philadelphia’s politicians closed down the city, it was too late.
A different story played out in St. Louis, just 900 miles away. Within two days of detecting its first cases among civilians, the city closed schools, playgrounds, libraries, courtrooms, and even churches. Work shifts were staggered and streetcar ridership was strictly limited. Public gatherings of more than 20 people were banned.
The extreme measures—now known as social distancing, which is being called for by global health agencies to mitigate the spread of the novel coronavirus—kept per capita flu-related deaths in St. Louis to less than half of those in Philadelphia, according to a 2007 paper in the Proceedings of the National Academy of Sciences.
From what I can see, the story isn’t just that St. Louis had fewer deaths per capita at peak. Instead, the city emerged from the pandemic with fewer “total excess deaths” overall. They flattened the curve and they lowered the toll in absolute terms. (If I’ve got that wrong, please correct me.) More people stayed alive under early social distancing than under late social distancing.
St. Louis and Philadelphia were 900 miles apart in an era before inexpensive air travel, so I don’t see how herd immunity in Philadelphia, achieved through widespread illness and death, would have snuffed out the virus in St. Louis, too.
I suppose it’s possible viruses have a natural ebb and flow; I haven’t read enough to know whether that’s the case. Maybe St. Louis hunkered down until the virus retreated for reasons of its own.
But given the importance of viral dose, isn’t it possible that St. Louis developed herd immunity via low-dose exposure?
Is it possible that we’re doing the same thing now?
I sure hope so.
Know your enemy
Can lockdown produce herd immunity with fewer deaths?
Social distancing and immunity
gasstationwithoutpumps on viral load and COVID-19 models
Social distancing and the 2nd wave
Viral dose, viral load