Do not rely on a negative antigen test if it is performed immediately after the onset of symptoms; this is what researchers at Boston Children’s Hospital in the US recommend after measuring the amount of virus present in Covid patients. .
For their study, the scientists included 350 people, most of whom suffered from coughs, sore throats, and runny or stuffy noses. “91% were already vaccinated, infected, or both, indicating a high level of immunity in this population.”they note.
Three days of incubation
Their results were published in the journal at the end of September Clinical infectious diseasesreveals the evolution of Sars-CoV-2 dynamics since the appearance of the Omicron variant.
“Early in the epidemic, many studies showed that viral load peaked at the onset of symptoms and declined sharply thereafter.”, – recalls Jeremy Guedge, Research Director of Inserm. However, the higher the level of virus in the body, the greater the chances that the screening will be positive. Hence the recommendation given by the health authorities to conduct an antigen test immediately after the appearance of clinical signs, and if necessary, to repeat it after 48 hours.
But this pattern has changed, the study shows. Viral load is now highest four days after the onset of symptoms. “This explains why antigen tests have seemed less sensitive in recent months. they were done during symptoms, often too early to be positive.comments Epidemiologist of the University of Geneva, Professor Antoine Flao. In fact, they are still as effective, but on the fourth day of the illness.
The phenomenon is accompanied by a shortening of the incubation period, which has passed from five to three days after Omicron’s arrival. In summary, symptoms appear more rapidly after infection than at the beginning of the epidemic, without knowing whether this change is due to variants or acquired immunity in the population. In the research, scientists are in favor of the second hypothesis.
What are the specific consequences? If PCR tests remain sensitive at any time of infection, “Antigen tests should be repeated, especially when you do them yourself at homeemphasizes Jeremy Guedge. The worst thing would be to think you’re safe just before your viral load peaks, which coincides with peak infectivity.”
The virus is now benign for most people, but Professor Flaault advises that people with immunodeficiencies should opt for PCR tests to save time. Antiviral treatment should actually be taken within five days of the onset of symptoms.
Source: Le Figaro
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