The reduction in viral load in humans infected with the Omicron variant of the coronavirus is felt only after the booster (third) dose of the vaccine, as shown by a new swiss scientific research.
Researchers at the University of Geneva (UNIGE) and the University Hospital (HUG) in Geneva, led by Professor Isabella Eckerle of the Department of Medicine, published in the journal Nature Medicine, studied nearly 600 symptomatic patients with Covid-19 vaccinated and non-vaccinated, in which the infectious viral load was measured. This load is a key factor – though not the only one – that determines how contagious a person with coronavirus will be to those around them. The study compared viral load in three groups of vaccinated and non-vaccinated patients (with initial variant, Delta and Omicron) during the first five days of symptomatic infection.
The study found that Delta causes a significantly higher viral load both in relation to the initial coronavirus variant and in Ομικρον. Vaccination also reduces the viral load if a vaccinated person becomes infected with either Delta or Omicron. People with Delta infection had significantly lower viral load after two doses of vaccine mRNA (Pfizer / BioNTech or Moderna) than those without vaccination infected with the Delta variant.
However, while in the case of Delta the reduction of the viral load is achieved from the first two doses, in Omicron this is observed only after the third dose. According to the researchers, only people who had taken a booster dose had a reduced viral load in the case of Omicron infection, while those who had taken only two doses had no benefit in terms of their viral load compared to the unvaccinated.
As Dr. Eckerle put it, “This is not paradoxical from an immunological point of view, as many vaccines require three doses several months apart to elicit a lasting immune response, e.g. occurs with the hepatitis B virus vaccine ‘.
In addition, the high infectivity of Omicron – greater than all previous variants – appears to be related to factors other than viral load. Why is Omicron so contagious, if its viral load is less than that of Delta and the other variants that preceded it? “We do not know yet, but the data show that other infectious mechanisms play a role,” said Pauline Weather, director of the HUG-UNIGE Center for Emerging Diseases.
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