Suppose a person with COVID-19 coughs into a bag. Let the bag sit in the sun for, say, 72 hours -- so as to make the virus inactive.

Could a healthy person breathe in the inactivated virus from the bag (perhaps done multiple times) to (eventually) trigger an antibody response to the virus?

Is this a known way to make inactivated vaccines? Has it been studied, perhaps for other viruses?

Are there known reasons why this would not work?

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    Coughing in a bag and leaving it in the sun may be cheap and easy: those aren't the hard parts. The hard parts are having a vaccine that produces enough of an immune response to protect against future exposure, and a vaccine that is safe enough to not cause illness directly in the people it is given to. Once you plan to test those two things, well, it turns out there are much more reproducible ways to do the cheap and easy steps.
    – Bryan Krause
    Commented Apr 20, 2020 at 22:38
  • Suppose this cheap and easy method was subjected to the same 4 phase testing as a normal vaccine. If it passed, it would have an advantage over normal vaccines of being more cheaply and quickly implementable all over the world. Unless there is an a priori reason why this wouldn't work, wouldn't that advantage mean this method warrants consideration?
    – unutbu
    Commented Apr 21, 2020 at 0:23
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    'Unless there is an a priori reason why this wouldn't work' Quality control. As @BryanKrause point out, you need something that's safe but effective. With your method you have no control over how many virons are coughed into th bag, and you don't know how many are killed in the sunlight. Each time you tried this it would be pot luck whether you were just infecting them with the disease, or just wasting their time because no immune response was provoked. The hard work of producing vaccines is creating something that works reliably for many different people. Commented Apr 21, 2020 at 1:33
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    You might look on this at some of the questions on variolation on this site. This was a crude form of vaccination for smallpox. You'd collect some scabs from smallpox blisters and rub them into a cut on an uninfected person. If they were lucky they got a mild case of smallpox and were then immune. If they were unlucky they got a bad case of smallpox and died. As with your suggestion, there was no way to calibrate the dosage. Commented Apr 21, 2020 at 1:42
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    Are there known reasons why this would not work? I think the more important question is - is there any evidence whatsoever that suggests this even remotely has a hope of doing anything beneficial at all. I'm curious about what would give you the idea that this could possibly be effective?
    – J...
    Commented Apr 21, 2020 at 18:01

2 Answers 2


The only approved inhaled vaccine is the flu vaccine delivered intra-nasally. It uses a live attenuated virus. There are a whole list of people who should not receive it because it's a live virus, and it works better for children, but only is 40% effective for adults.

The main issue is

The intranasal LAIV, recommended for children above the age of 2 years, induces a broader immune response wherein protection is not antibody mediated and probably involves undefined multiple correlates of protection.

and that's with a live virus.

How well would a dead inhaled virus work? Well, we have some data from MERS that suggests that vaccination with whole dead virus can increase lung pathology when exposed to live virus.

The implication of the current study is that application of an inactivated MERS-CoV vaccine for prevention of MERS in humans may carry a risk for lung immunopathology if subsequently exposed to MERS-CoV. The study also leads us to suggest that the extensive background of preclinical experience with inactivated SARS-CoV vaccines may be applicable to inactivated MERS-CoV vaccines.

So, your cheap vaccine may increase your risk of death or disease when exposed to the live virus.

Influenza Vaccination Strategies: Comparing Inactivated and Live Attenuated Influenza Vaccines https://www.cdc.gov/flu/prevent/nasalspray.htm

Immunization with inactivated Middle East Respiratory Syndrome coronavirus vaccine leads to lung immunopathology on challenge with live virus https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5027702/

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    Why does it increase lung pathology? What is the mechanism? Commented Apr 22, 2020 at 13:45
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    You need to ask a separate question Commented Apr 22, 2020 at 20:26

It wouldn't be consistent. (as some of the commenters pointed out).

Here are some numbers:

  • The concentration of virus in sputum can vary by a factor of 10^5. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7224694/ for count of RNA in sputum)

  • Best guess is that 100-1000 RNA copies is a "quanta" in the Wills-Riley Model (http://tinyurl.com/covid-estimator)

  • If it's known how many RNA copies is good to generate immune response but not disease, it's very hard to get the right level.

  • There will be variation in immune response / disease contracting.

But, this doesn't rule it out as possible. In fact, nothing can prove it's impossible except running every variation of what you're saying. To prove it's possible, you would need to run the controlled experiment.

But that experiment would be considered unethical.

You could try it in rats or mice first. But there is no good animal model for COVID19 right now (from what I read).

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