This paper reports on contact tracing efforts in China (SSRN Paper) About 49,000 CV-19 patients identified over 277,000 contacts. Out of this group of contacts, 3152 people who were asymptomatic had positive tests and 50 of those were determined to be false positives. 2928 of the patients were asymptomatic throughout quarantine and 174 turned out to be presymptomatic. The average time from test to symptom onset was a very long 9.7 days.
This study was a meta-review of infectiousness in CV-19 cases. (SSRN Paper) The authors found 79 applicable papers. Viral shedding is the process by which people exhale or otherwise expel the virus from their bodies. The viability of the virus expelled, the amount and the duration of time for which the shedding occurs obviously have a lot to do with a person’s infectiousness. The combined findings were that upper respiratory tract shedding occurred for an average of 17 days and lower respiratory tract shedding for 14.6 days. No study found live virus being shed after 9 days from symptom development. The peak of shedding was in the first week of illness.
This is an interesting piece of research from Brazil on whether stay-at-home orders and social isolation actually made the epidemic worse. (SSRN Paper) The researchers used cell phone data to determine mobility of Brazilians. They purport to find that deaths were higher the lower mobility was, with a 39 day lag. Social isolation supposedly caused a higher peak of deaths, and for that peak to arrive sooner. I am not sure I buy into this, although I do think that encouraging people to stay at home only facilitates household transmission.
Along those lines, here is a modeling study that also suggests that widespread lockdowns may increase total mortality. (Medrxiv Paper) The researchers used Europe as the example for their modeling. If people under 60 were pretty much allowed to go about business as usual, total deaths were estimated to be lower, presumably because more infections would occur and population immunity levels would slow transmission of the virus, including limiting transmission to more vulnerable elderly persons.
And in another modeling approach, these researchers claim that from viral load distributions in the population, the course of the epidemic can be calculated. (Medrxiv Paper) They used cycle numbers from PCR test results to estimate viral load. Using Massachusetts as an example, they project trajectory from viral load data. They suggest that all PCR test results should include this data so that it may be used instead of or in addition to pure case counts to understand what is happening with the epidemic in a specific location.
More research on testing, again looking at use of saliva samples. (Medrxiv Paper) Saliva testing is believed to be easier on patients than nasal swabbing. The authors looked at over 2000 samples and found that in general saliva sampling had poor accuracy levels, but that it did a good job of identifying persons with medium and high loads of virus, i.e., those persons most likely to be infectious.
And we finish with good news, another study confirming that almost all CV-19 patients have a lasting (at least six months) antibody and T cell response to infection. (SSRN Paper) At a time when people are talking about a handful of reinfections meaning there is no persistent immunity, it is worth recalling that every study suggests that these are rare exceptions. It is also reflects a misunderstanding of adaptive immunity. I keep trying to explain, it isn’t some absolute physical barrier; it is the creation of a rapid reaction force that is able to clear the virus faster in the event of any re-exposure. Re-exposure is going to happen, constantly. In this study, from China, 418 patients were followed for an extended time. 98% of the patients had measurable levels of neutralizing antibodies after 6 months. Patients who had had severe disease tended to have higher levels of antibodies. In addition, all patients had measurable T cell activity. So don’t worry about the re-infection nonsense. People who are infected develop a sufficient adaptive immune response to be a factor in slowing transmission.