Here is another study on transmission dynamics. (Trans. Article) The researchers sought to ascertain what comes out of our mouths as we breathe, talk, cough, etc. There is an extended discussion of droplet sizes and dispersal. Then they built a model, so this is not actual research on people doing these activities. Most droplets fall to the ground or another surface quickly, especially in the absence of wind. With wind, and presumably artificial air flow movement, the droplets can travel longer distances. The study appears to identify minimal risk from breathing, with coughing obviously creating the most droplets.
A professor of epidemiology, Sunetra Gupta, gives a very rational perspective on the epidemic in an interview. (Gupta Interview) She believes the epidemic started earlier and has spread more widely than is widely accepted. She thinks that this created immunity levels that slowed the epidemic, not the lockdowns. She also notes the extreme age spread of cases and deaths. She believes case fatality rates are very low for the general population. He says that the lockdowns are a “luxury” for the middle and upper income groups and a tremendous burden on low-income people.
Here is another study on antibody development (Medrxiv Paper) This paper looked at 46 patients in Italy with confirmed coronavirus disease and examined antibody development over time. 35 uninfected patients were used as controls. None of the controls tested positive for antibodies. The patients tested at a later time point all had some antibody response by 15 days after symptom development, as did almost all of those tested earlier.
And this one is working on the same subject. (Medrxiv Paper) A group of hospital workers with mild disease in France was studied for antibody development. 160 of these workers had infection with mild or no disease. One test detected antibodies in 153 of these people and another test in 159. By a month after symptom onset, 98% of these people had neutralizing antibodies, which aid in the elimination of the virus. This neutralizing activity increased over time.
And one more antibody study. (Medrxiv Paper) This is a large study on 1850 patients in China, tracking antibody development over the course of the disease. They found that antibody development was later for patients with serious disease than those with mild or moderate disease but these serious illness patients had higher antibody levels at least while in the hospital. Only one test was used for the analysis. The level of antibodies conferring long-term immunity tended to rise during the treatment phase and thereafter. The type of antibody that is most present during an actual infection rose in the treatment phase but declined thereafter as you would expect. 97% of patients developed long-lasting antibodies.
There have now been a large number of antibody studies. Here is what I think I have gathered from all of them. Almost all infected patients, even those with mild disease, develop strong antibody responses. Some people may also have antibodies and other immune defenses that were developed in response to other strains, but also work against this one.