If a SARS-CoV-2 asymptomatic infected individual is exposed to a high viral load, could they develop COVID-19 disease?

Question

I would add my own research if I could to respect site rules, but I can't. There are no studies on SARS-CoV-2, all I can find is for SARS-CoV-1 and some Chinese information based studies.

My government is planning to do massive testing (when tests are available) and transfer and isolate every asymptomatic person in buildings such as hotels. The right is in arms saying this is like gulags and saying now they don't want to do the test.

My question, I hope generically, is: if someone is infected but asymptomatic, could the exposure to a high virus load lead to COVID-19 disease?

Or conversely: if your immune system is already coping well with the virus, the addition of more virus load can't worsen your diagnosis.

Answer 1

What your government is proposing is a lot less than what was actually done in China. There, and perhaps that is still the case, large numbers of asymptomatic infected people were housed together in halls with only social separation between them, and masks to prevent others from infecting others.

Your government is proposing to house the asymptomatic infected in hotels, presumably in separate rooms.

We know that people who are infected because they have virus identified using PCR swabs of their upper airways. CT scans can show pulmonary lesions present even without cough or fever. And even speaking can aerosolize virus though you are likely most infective at about days 4-5 before your own antibody production has ramped up significantly.

So, it's likely you are exhaling virus, and inhaling again the virus that you exhale, as well as spreading virus in your blood to other tissues. It seems less likely that you're going to inhale a viral load that already exceeds the amount of virus coating your mucus membranes and alveloli. At least you will have some antibody production after day 5 or so on average to provide some protection.

Note also that even within family groups housed together in Guangzhou, the incidence of cross infection was only 10%.

And there are likely to be host factors at work. We know that women and younger people have a less severe course generally. So, even with a higher viral load on re-exposure, that may not change the underlying host factors that might =give them some protection eg. higher levels of ACE2 receptors, Group O blood group etc.

https://www.who.int/docs/default-source/coronaviruse/who-china-joint-mission-on-covid-19-final-report.pdf

Answer 2

You may find this article to be helpful in some way. Dr. Siddhartha Mukharjee The New Yorker April 6 2020 issue. “How does the Coronavirus Behave Inside a Patient”

The title I think is a bit misleading. The article does not cover the whole course of the illness! I think. It is interesting https://www.newyorker.com/magazine/2020/04/06/how-does-the-coronavirus-behave-inside-a-patient

This covers more first, early, early repeat exposures.

The inoculum viral load and such is discussed.

I don’t think this a perfect answer to OP’s question but it may be helpful in some way.

Author bio: https://en.m.wikipedia.org/wiki/Siddhartha_Mukherjee

Answer 3

Doing such an experiment on humans would obviously be unethical in the present circumstances. There has been a report that monkeys who recovered and were later re-infected with mega-doses of the Covid-19 virus didn't get sick again. This is not terribly conclusive, because monkeys don't get severe symptoms from SARS like we do, for example. (SARS is the closest relevant relative to the Covid-19 virus aka SARS-CoV-2.)

Immunity to a pathogen, in general takes about 3-4 weeks to develop to develop fully, so if you [get] re-infect[ed] with a larger dose within this window, even a after a vaccine, you can cause/get the disease, although it's apparently a pretty rare occurrence.

These individuals were likely resusceptible to reinfection with the same strain of influenza virus due to a confluence of unusual events. First, all three were reinfected within three weeks, before their primary adaptive response had sufficiently matured. Another contributing factor was the high level of circulation of the pandemic strain. [...]

Could reinfection also occur after immunization with influenza vaccine? Yes, if the immunized individual encounters the virus before the primary antibody response matures, which occurs in 3-4 weeks. This is more likely to occur during pandemic influenza when circulation of the virus is more extensive than in non-pandemic years.

[Citing:]

Perez CM, Ferres M, & Labarca JA (2010). Pandemic (H1N1) 2009 Reinfection, Chile. Emerging infectious diseases, 16 (1), 156-7 PMID: 20031070

---

About the Fangcang-style hospitals (i.e. make-shift hospitals for those with mild or asymptomatic infections), which China says it closed the last one on March 10 (after there were 13 opened in Wuhan at the peak); it turns out they used now in other countries, and they are even a WHO recommendation of sorts (as of March 17):

WHO recommends that all laboratory confirmed cases be isolated and cared for in a health care facility.

[...]

If all mild cases cannot be isolated in health facilities, then those with mild illness and no risk factors may need to be isolated in non-traditional facilities, such as repurposed hotels, stadiums or gymnasiums where they can remain until their symptoms resolve and laboratory tests for COVID-19 virus are negative.

According to the (April 2) Lancet paper on Fangcang hospitals, they Chinese took various precautions to prevent cross-infection with other diseases in such settings. How strictly these measures have been implemented and how well replicated in non-Chines Fangcangs elsewhere, I won't venture to comment here, but CNN had a somewhat disparaging article about Fangcang hospitals back in February, outlining their shortcomings. Since then, the US has been arranging similarly looking facilities in the NY area, but I don't know how they intend to use them.