New image of Omicron variant detected at National Institute of Infectious Diseases

An electron microscopic image of a novel coronavirus of the Omicron variant has been isolated successfully at the National Institute of Infectious Diseases The saliva of patients infected with the Omicron variant of COVID 19 virus contains a larger number of novel coronaviruses in a state that is more susceptible to transmission, according to a team of Japanese scientists.

They say that saliva droplets with larger amounts of viruses go farther and last longer in the air than droplets from patients infected with the original virus strain.

Kenichi Imai, a professor of infectious diseases and immunology at the Nihon University School of Dentistry, said that the state of the viruses in saliva may be a factor in the spread of the Omicron variant through aerosol transmission.

The researchers said that the discovery likely accounts for why the waves of Omicron infections have been dragging on, and that it will be essential for people to ventilate spaces and wear masks in the days and months to come.

The research results were published in a scientific journal of the American Medical Association on January 10.

The Omicron variant, which caused the sixth wave of COVID 19 cases in Japan last winter, has remained the mainstay virus strain in outbreaks, including the current eighth wave.

It had been learned that the Omicron variant replicates faster in bronchial cells than the Delta variant, which caused the fifth wave in the summer of 2021.

The state in which virus particles of the Omicron variant are contained in saliva, which is responsible for aerosol transmission through fine droplets, remained a mystery.

Imai and his coworkers collected saliva samples from 90 COVID 19 patients who visited a Nagoya clinic between November 2020 and February 2022.

The researchers used centrifugation and genetic testing to determine the state of the novel coronaviruses of the Omicron variant, the Delta variant and the original non-mutant strain in the patients saliva.

The study showed that virus particles exist in saliva in two states.

In one, the particles are associated with cells detached from the interior of the mouth, either contained in those cells or attached to the periphery thereof. The particles are unassociated with the cells in a cell-free state.

The team focused on virus particles in the cell-free state. Their count was 3.21 million per cubic centimeter of saliva for the Omicron variant, or about three times the count of 1.17 million per cc for the Delta variant and 18 times the count of 180,000 per cc for the original virus strain.

Cells derived from the mouth's interior measured at least 0.01 millimeter, and large droplets containing similar cells fell after traveling 1 to 2 meters.

Cell-free viruses, by contrast, are contained in fine droplets that measure 0.005 mm or less, which travel farther and stay in the air longer.

In the future, it will be important to study the ratio of cell-free viruses in saliva during the early phase of the emergence of a new virus variant, Imai said.