Some Thoughts on Seasonality, Death Rates and Reinfection

Okay, first a little serious research that is very interesting.  The National Academy of Science (in this case its sub-branch the Academy of Medicine) has groups that are available to provide rapid expert consultation to the government on critical matters.  They have been busy in regard to coronavirus.  Yesterday one of their panels released a letter regarding potential seasonality of the coronavirus.  (NAM Letter)  This is an issue of some importance because in general coronavirus infections reveal a seasonal pattern and lighten up in the warmer months.  The experts reviewed the existing scientific literature and discussed studies under way.  The underlying issue is whether the virus transmits or survives better under certain temperature and humidity conditions than others.  As you might imagine, there are not a lot of studies yet on this issue. But what exists suggests the virus exhibits less survival under high temperatures but that also depends on the type of surface.  More tests are being run with results expected soon.  Even less information is available on the effects of humidity, but there is some evidence that higher humidity is inimical to virus survival.  Studies comparing the spread of the virus in different climates also supported this notion, but the panel cautioned that this could be due to confounding factors.  In some experiments the virus exhibits fairly long survival times, on the order of days.  While coronaviruses that cause colds appear to be seasonal, the original SARS and MERS coronaviruses did not.  The panel also noted that the lack of widespread immunity would ameliorate any seasonal effects.

You have to be so careful not to be beguiled into believing anything that is sensationalized or seems extreme.  It might turn out to be true but probably not.  Here is one issue occasionally mentioned now; that some patients who apparently were recovered from the infection became reinfected.  The evidence for this is said to be both clinical and lack of antibodies in supposedly recovered patients.  I would be very cautious about accepting this possibility.  First, it is generally patients’ immune systems that ultimately remove the virus, and I would suspect that cases where the infection is eliminated by purely pharmaceutical or other means are rare.  A patient’s immune system would always be involved in some manner.  And while some people may have weak antibody responses, some level should be there.  Some of these cases likely involve substantial but incomplete clearance of the virus, leading to a perception that the patient had recovered, followed by resurgence of the virus.  Others may well involve false positive coronavirus tests in patients with influenza or other respiratory illness. So the patient wrongly is diagnosed with coronavirus initially, but may actually have it by the time of the second test.  Other both tests could have false positive results.   Some tests have relatively high false positive rates.

Another item I would be cautious about is concern other deaths being accurately or inaccurately attributed to coronavirus and CDC and health department instructions regarding death certificates.  I wrote about the CDC guidance in another post, and while I think there are issues, I am not sure I would ascribe any bad intent.  Some people have suggested that deaths are undercounted because of people who die at home or patients who were never tested but may have had coronavirus.  Others believe that too many deaths are being attributed to coronavirus that may be due to other respiratory illnesses.  No matter what the true state of affairs is, a lot of people are almost certainly dying either with or because of coronavirus.  The issue of cause is the one of most interest because many of these people had pre-existing conditions or frailty which made them far more susceptible to serious illness and death.  Should those all be coronavirus deaths?  And I suspect there is a fair amount of substitution of coronavirus death for influenza death.  At some point researchers will do more careful studies and ascertain more accurate attribution of death, but unless the number of errors is truly large, it shouldn’t change the perception that this is a serious public health issue.