After Houston, Texas experienced a devastating second wave of COVID-19 cases a few months back, researchers honed in on genetic sequences important to the novel coronavirus’s transmissibility
This exploration yielded two significant finds–one alarming and previously covered here, and the other encouraging.
According to new data presented at the European Society of Clinical Microbiology and Infectious Diseases’ Conference, SARS-CoV-2’s viral load (which denotes the numerical expression of the virus in a given volume of fluid), is declining among affected populations alongside mortality rates associated with COVID-19.
Declining SARS-CoV-2 viral load
Assessing a cycle threshold (Ct) value via nasal swabs is a reliable way to clinically assess the viral material present in a subject; the higher the Ct count, the lower the viral load.
A high viral burden is calculated at a Ct of 25 and under, intermediate loads are calculated between 26 and 36, and low viral loads at a Ct over 37.
“To date more than 25 million cases of SARS-CoV-2 infection have been reported worldwide, with the majority of cases being reported in the United States so far,” the Wayne State University researchers explained during the webinar. “In this study, we present data describing the downward trend in the initial SARS-CoV-2 viral load.”
The authors were quick to note in the paper that preceded the conference that data on SARS-CoV-2’s viral load in relation to community risk has been poorly characterized.
In their retrospective analysis (collected from patients between April 4 and June 5) it was determined that 49% of participants evidenced an intermediate viral load count, while low and high viral load counts accounted for a little more than a quarter of the study pool. Forty-five percent of patients with high viral loads succumbed to COVID-19.
Conversely, low viral counts represented 70% of patient samples by the first week of May, and only 32% of subjects with intermediate loads and 14% of those with low viral loads succumbed to the respiratory disease.
“During the April-June 2020 period of the COVID-19 pandemic, the initial SARS-CoV-2 load steadily declined among hospitalized patients with a corresponding decrease in the percent of deaths over time,” the authors wrote in a media release. “Though confounding variables have not been evaluated, this suggests an association between initial viral load and mortality. Rapid implementation of social distancing measures, lockdown, and widespread use of facemasks may have contributed to a decrease in exposure to the virus.”
Early on, the Lancet speculated that viral load in COVID-19 was linked to disease infectivity, morbidity, and mortality.
The New England Journal of Medicine proposed that communities exposed to a comparable degree of viral debris enjoy a stronger immune response through a process known as variolation.
It should be noted that there are two distinctions to be made with respect to early risk stratification, even in the event that both or neither theory are deemed to be conclusive:
It is generally believed that the former more faithfully determines COVID-19′ severity. Though the latter may be instructive of a person’s infectious potential.
“Diseases in which your immune system has a big role to play in how sick you get — and your immune system contributes to pathogenesis — do not seem to be able to handle a large viral inoculum,” concluded Monica Gandhi, MD who worked on the study recently published in the New England Journal of Medicine.