The ORDER in which Covid-19 symptoms such as fever or cough appear is related to the variant of the virus. Not to the geographic, climatic or genetic background of the patient. A study by Peter Kuhn by the University of Southern California, published on PLOS Computational Biology. The analysis in particular focused on variant D614G, which emerged between late January and early February 2020 and became dominant before being replaced by the English or Alfa. Not only does he conclude that the order of Covid symptoms changes with the mutation in the viral disease, but he also speculates that the D614G variant may have been particularly transmissible because infected people were more likely to cough in public, before the onset of fever. .
Relationship between symptoms and variants
It is not the first time that symptoms and variants have been linked. “A study done in the United Kingdom and referring to the Alpha variant already recorded how the loss of smell and taste were less frequent with the variants subsequent to that of the original strain. While the usual symptoms (fever, cough, fatigue, headache) present with the ancestral variant of Wuhan and with the variant D614G there was a higher incidence of disorders affecting the digestive system such as diarrhea and vomiting and a lower finding of loss of smell and taste “, he recalls Roberto Tail, director of the Infectious Diseases Complex Operational Unit of the Gemelli Hospital in Rome. He adds: “The new study certainly presents aspects of interest because through a mathematical analysis it analyzes the frequency of the most common symptoms of the disease in relation to various parameters of a geographical, temporal nature and presence of the D614G variant”.
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Fever first symptom in China, cough in the United States
At first, the team of researchers from the University of Southern California developed a mathematical model based on data from the initial epidemic in China in early 2020, drawing up an order in the appearance of symptoms. He then focused on understanding whether this order varied in patients from different geographic regions or with different characteristics.
Based on 373,883 cases in the United States between January and May 2020, the researchers surprisingly found that the order of symptoms differed between the initial outbreak in China and its subsequent spread in the United States. While in China fever preceded cough and nausea / vomiting was a third symptom, in the United States cough was the first symptom, cough the second, diarrhea the third.
The predominant presence of the D614G variant in early 2020 in the United States was associated with a higher likelihood that cough was the first Covid-19 symptom in those who fell ill. Furthermore, when the same variant entered Japan and supplanted the original Wuhan strain, the order of symptoms in the country changed.
By analyzing additional data from Brazil, Hong Kong and Japan again, the researchers confirmed that the different symptom orders were not associated with geographic region, weather conditions or patient characteristics such as age and comorbidities. They were associated with the SARS-CoV-2 variants.
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The hypothesis: cough as the first symptom makes the virus more transmissible
The study also hypothesizes that the increased transmission of the D614G variant is related to the order of symptoms, hence the onset of cough before fever. An explanation of the transmissibility of the variant that has become dominant at a certain point, which however may not be the only one. “From this substantial analysis it emerges that the frequency of the most common symptoms changes with the appearance of this variant that puts cough in the first place: by favoring the transmission of the virus it could be more contagious than the previous one. It should however be noted that there have been several studies who indicated that this greater transmissibility and therefore the increase in infections linked to the D614G variant (and other more recent variants) depends on the Spike mutations that increase the infection and transmission capacity of the virus towards the host cells. since it correlates symptoms with D614G, it has not yet matched the other more recent variants (alpha Delta omicron) even if all of these have D614G “, comments the infectious disease specialist.
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