A Head Full of Coronavirus Research, Part 96

Anyone who thinks that research and data isn’t being pivoted on a dime to suddenly help the new administration is delusional.  In the latest example, the CDC has discovered that it may be safe to send children back to real school.  (CDC Study)    The study took place in a rural school district in Wisconsin which had in-person schooling during the study period, September through November.  There was substantial community transmission at the time, and the rates of infection among both students and staff were substantially lower than those in the community.  Not one case among a staff member was acquired at school and only seven student ones were.    The public health community should be deeply ashamed of its failure to actually consider the totality of public health during the epidemic, and what has happened to children is exhibit A.

Another meta-review on the rate of transmission by asymptomatic persons.  (JAMMI Article)   Thirteen studies deemed to have low risk of bias from seven countries and covering about 21,700 people were included.   The focus was on high-risk populations.  Across the studies the asymptomatic (true asymptomatics, not pre-symptomatics) percent was 4% to 41%, and the authors’ meta-analysis estimated a 17% asymptomatic case rate.  Interestingly, the asymptomatic rate was higher in aged care settings than in the general community.  The relative risk of transmission from an asymptomatic case was only 42% that of a symptomatic one.

Why has southeast Asia has such a low rate of CV-19 cases?  Maybe climate and latitude, but also likely that there is a high level of pre-existing immunity due to multiple exposures to various strains of coronavirus similar to CV-19.  This study describes one of those.  (Medrxiv Paper)   CV-19 appears to have jumped from a bat species.  Researchers have begun going back and looking at stored samples of blood from bats.  This particular species was identified from a 2010 sample and has a very substantial sequence similarity with CV-19, over 92%.  It is highly likely that if there was human contact with this strain, it would have led to some adaptive immunity.

Another study of the impact of meteorological variables, particularly temperature and humidity.  (Medrxiv Paper)    The researchers did a number of adjustments to try to correlate case levels with these factors.  The found that, within a range, lower humidity and lower temperature were associated with more cases, presumably reflecting more favorable transmission conditions.

One of the foreseeable, although perhaps unintended consequences, of the lockdowns and campaign of corona-terror, was a decline in use of needed health services.  One of the worst of those is a substantial drop in immunizations, especially childhood immunizations.  This paper details the impact of missed immunizations.  (Medrxiv Paper)   The focus is on developing countries, which bear a significant burden from infectious disease.  Missing immunizations leads to a substantial increase in mortality and disease burden in these countries.

Did closing non-essential businesses lessen transmission and cases?  This study examines the question in Pennsylvania.  (NBER Study)   The study period only went through April.  The data came from one large health plan in Pennsylvania and covered only commercial members, that is, those likely covered through their employer.  The data used did not allow for identification of where or how a person was likely infected.  And it could not be adjusted for possible testing variations across sub-populations.   It also was not clear that it was completely adjusted for potential confounding variables like more minority or low-income persons or persons in households with higher numbers of members being more likely to experience a case.  The authors found that essential workers were significantly more likely to contract CV-19, and that household members of an essential worker were also more likely to become infected.  There is a logic to that finding, as one might assume that essential workers had more contacts and potentially more exposure, but the limited time period included, which is surprising given that it is now almost 8 months ago, is the most significant problem with the study.

Another modeling study, this one again focused on the potential role of heterogeneity in susceptibility and infectiousness and how that may affect the level of infection at which transmission substantially slows in a population.  (Arxiv Study)   Without belaboring the details, these authors again suggest that variability in these factors may mean that there is a lower level for population immunity than traditionally assumed.  I have become somewhat more dubious of this due to high levels of prevalence observed in some areas, for example 70% in a region of Peru, and estimates that in the US some states may have 50% or more of the population infected.   I believe there is individual variation in ability to be infected and in rate at which infection is passed, but I think the most important variability is in contact rates.  Even there, however, everyone has some level of contacts.  Worth a read.