This is an interesting discussion of issues around asymptomatic cases of CV. (RCS Article) The author is a physician, albeit not an infectious disease doctor or epidemiologist, and explores a number of important questions around asymptomatic cases, including their role in transmission and why they are asymptomatic. He seems to have a pretty neutral viewpoint and appears to conclude that allowing spread may be a good option, as long as it occurs in circumstances which favor development of mild cases.
I really don’t know what to think about the influence of weather, climate or solar insolation on transmission. As I have noted, those factors might affect virus viability or may do something to human behavior or biochemistry that does limit or encourage transmission, and there is macro level evidence that might suggest geographical patterns of case surges and reductions, but I suspect it is pretty complicated. In any event, these researchers looked at the correlation of cases with certain weather measurements in the Netherlands. (Medrxiv Paper) The researchers attempted to ascertain a relationship between humidity and influenza over the past five years and apply that to coronavirus. Their end conclusion was that higher humidity is associated with a reduction in cases. I am dubious.
This study examined children and coronavirus. (Medrxiv Paper) 382 children, aged 21 and under, who had close contact with an infected case were tested and followed. 293 were positive. Being hispanic, and 80% of the children in the study were hispanic, and not having asthma and living with an infected child were correlated with a greater likelihood of being positive. Many cases were completely asymptomatic, particularly in children aged 6 to 13. Viral loads were the same across asymptomatic and symptomatic cases and diminished rapidly after symptoms developed. Only one of these children was hospitalized.
Readers know that I am fascinated by the physical dynamics around the virus’ encounter with a human. This paper describes a modeling approach to understanding that interaction in the respiratory tract. (Medrxiv Paper) It is only a model but the paper has lots of information and discussion about the respiratory tract and factors that might influence whether the virus reaches the lungs. As you would expect, even with a strong immune system response, the dose of virus entering the respiratory tract has a lot to do with the severity of infection.
An Austrian ski town had one of the earliest outbreaks in Europe and a followup study of prevalence is presented in this paper. (Medrxiv Paper) The antibody testing was conducted in April and used multiple assays for greater accuracy. 1473 people were tested including 214 children. 42% were positive, but only 27% of children age 18 and under. 84% of those positive had not been previously diagnosed as positive. The usual very high rate of asymptomatic cases. Now note this carefully. Of 478 households, 124 had children. 84 of these had no positive children and 51 of those 84 did have a positive adult. In only one of the 124 households was there a positive child but no positive adult.
Another cross-reactivity study from an international team of researchers suggests that antibodies developed in the course of CV19 infection will have a response to the other coronaviruses. And that antibodies from infections with those coronaviruses will be cross-reactive to CV19. (Medrxiv Paper)
This is actually a pretty important paper because it deals with the under-appreciated problem of the accuracy of infection tests in low-prevalence populations. (Medrxiv Paper) The author points out that if prevalence of cases is low, even a test with a high accuracy can have low positive predictive value. Repeat testing or other strategies are needed to ensure that public policy isn’t guided by a mistaken reliance on test results. And asking for widespread testing in a population, for example school children, without careful construction of the program, is asking for lots of false positives.
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In The RCS article, the author lists as assumption #5 that the viral load a person receives is an important factor for disease severity. If so, it stands to reason that increasing asymptomatic and mild cases might allow us to reach herd immunity with minimal severe sickness and death. Which is all the more reason NOT to take measures to reduce transmission amongst children and young adults.