People who have been vaccinated against Covid-19 are not only well protected against serious illness in a so-called breakthrough infection, they are also less contagious than those who have not been vaccinated. Unlike the Delta variant, however, the Omicron variant requires three doses of vaccine to effectively reduce the number of infectious virus particles, Swiss researchers report.
The study by a team led by Isabella Eckerle and Benjamin Meyer from the University of Geneva refers to the omicron subvariant BA.1, not the subvariant BA.2, which is now dominant in Austria. “Our results underscore the positive effect of vaccinations beyond individual protection against serious disease,” researchers write in the journal “Nature Medicine.”
All corona variants considered
Between April 2020 and February 2022, the scientists took swabs of the nasal mucosa from a total of 565 people infected with corona in the first five days after the symptoms started. The study thus covers almost the entire course of the pandemic to date: infections with the originally circulating variant as well as with the delta and omicron variants were registered. Some subjects were not vaccinated, others were vaccinated twice or even boosted. Virtually everyone who had been vaccinated had received an mRNA vaccine (eg from Biontech/Pfizer or Moderna).
The scientists then determined the so-called Ct value, which indicates how much genetic material of the coronavirus is present in a sample. In addition, they determined the amount of infectious virus particles in a sample using cell culture experiments. This is a better indicator of the infectiousness of a sick person, as the researchers’ studies confirmed.
Booster pushes viral load to a fifth
The review of the data found that people who had been vaccinated twice had significantly fewer infectious particles in the upper respiratory tract than those who had not been vaccinated, at nearly a fifth. According to the study, vaccinated people were also able to fight the virus faster. In ommicron breakthrough infections, the amount of infectious virus particles after two vaccinations was the same as in non-vaccinated persons. Only a booster vaccination pushed the value back to about a fifth.
Another result: During the ommicron wave, the researchers found significantly lower amounts of infectious particles in the vaccinated subjects than during the delta wave – despite the greater ability of the ommicron variant to infect. They conclude that omicron-infected people are not more contagious because they shed more viruses. The mechanism of entry of the SARS-CoV-2 pathogen into the cell may be different.
The researchers point out that it is not known from what amount of virus particles detected an infected person is contagious. Fluctuations in the amount of virus may also be influenced by the particular quality of the smear or the fact that samples were not taken from all subjects at the same time of infection.
Source: Krone
I’m Wayne Wickman, a professional journalist and author for Today Times Live. My specialty is covering global news and current events, offering readers a unique perspective on the world’s most pressing issues. I’m passionate about storytelling and helping people stay informed on the goings-on of our planet.
