What is the minimal infectious dose (MID) of SARS-CoV-2?
Assuming the immune system is healthy,
How much SARS-CoV-2 virus (cause of COVID-19) is required to make a person sick?
This might also depend on time, if it was a high infectious dose but just some minutes, maybe not that bad outcomes.
Or if it's a very low infectious dose, but during a whole day, maybe a bad outcome.
In addition, Would it be possible that a person was exposed to SARS-CoV-2 virus, and so the virus got inside their system, and even still this person's immune system didn't let the virus to infect this person?
Note that it's not the case that this person will be totally asymptomatic, it's the case when the virus wasn't "strong enough" to infect this person even being inside their system.
MID - minimum infectious dose defined as"the smallest quantity of infectious material that regularly produces infection"
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Disclaimer: I am not entirely satisfied with this answer in as much as the author fails to source the claim that 1000 viral particles may be the threshold for infection. However the author has significant expertise and more importantly (to me as a non-expert) has written a piece that is entirely readable and plausible. I offer it for your consideration:
Dr Bromage The Risks - Know Them - Avoid Them posits that 1000 viral particles are sufficient to produce an inflection. He then discusses the risks of encountering that threshold and how to minimize one's risk.
Update:
The minimum infectious dose of SARS-CoV-2, the virus that causes Covid-19, is unknown so far, but researchers suspect it is low. “The virus is spread through very, very casual interpersonal contact,” W. David Hardy, a professor of infectious disease at Johns Hopkins University School of Medicine, told STAT.
Blockquote
STAT
For comparison purposes:
... it takes just 18 particles of norovirus to cause an infection. This can lead to the classic clinical signs of vomiting and diarrhoea
LINK, with citation to norovirus study for infectous dose
From this link How much of the coronavirus does it take to make you sick?
The amount of particles a person is exposed to can affect how likely they are to become infected and, once infected, how severe the symptoms become.
A high infectious dose may lead to a higher viral load, which can impact the severity of COVID-19 symptoms.
Viral load is a measure of virus particles. It is the amount of virus present once a person has been infected and the virus has had time to replicate in their cells. With most viruses, higher viral loads are associated with worse outcomes.
“The more viral particles that get into the lungs, the more damage to the lungs that is probably happening,” said W. David Hardy, a professor of infectious disease at Johns Hopkins University School of Medicine.
From this link Does The Amount of Coronavirus You're Exposed to Determine How Sick You'll Get?
A report from China suggested that there is no difference between how much coronavirus a person is exposed to and how sick they get.
But another report showed that patients with milder disease had lower levels of the virus.
It seems we are looking at the kinetics of viral growth in the body, the time to release of the cell containing the replicated virus, the amount of virus released per cell and the rate of adsorption of the virus into the cell. I don't speak with authority regarding the biochemistry of this process, but I do remember quite a lot about chemical kinetics. If the rate of replication of the virus in the body is faster than the rate of adsoprtion through the ACE-2 enzyme then you can launch all the virus you want at the cell, it is replicating the virus faster than the virus can penetrate cells. Similarly the time to release the virus from the infected cell and the amount of virus released per cell all contribute to the effect of any viral infection. See this for example doi.org/10.1016/j.virol.2011.12.005. This more recent article seemed to try to answer the question - but did not wwwnc.cdc.gov/eid/article/26/9/20-1495_article So it depends.. I guess.
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