For those wondering if #COVID19 is likely to confer immunity to re-infection or disease, here is an interesting study with a *different* common-cold human coronavirus that attempted to infect and then re-infect human volunteers (1/5)
https://www.ncbi.nlm.nih.gov/pubmed/2170159 

15 volunteers were experimentally inoculated with common-cold coronavirus 229E. In initial infection, 10 of 15 volunteers were infected. Ones that were not infected had higher serum IgG and nasal IgA, indicating that pre-existing antibodies help reduce risk of infection. (2/5)

After infection, antibodies rose, but by 1 year had declined substantially though still higher than pre-infection. Then attempted to re-infect all volunteers. All 5 not infected in prior year were infected second time, as were majority that had been infected year before. (3/5)

However, in the re-infection, only 1 had symptoms of cold, vs 8 in the initial infection.

So overall, for this *common-cold coronavirus*, pre-existing antibodies reduced risk of infection, but re-infection could occur a year later although with reduced symptoms. (4/5)

Results may be informative for #COVID19? But major caveats:
- different coronavirus, 229E vs #SARS_COV_2
- all volunteers probably been infected w/ immunity prior to 1st infection, which is not true for #COVID19
- 229E causes mild cold, so hard to assess disease severity
(5/5)