That omicron is transmitted more easily than its sister variants is already evidence that supports all the scientific literature that has emerged since its detection two months ago in South Africa. Added to the lengthy investigation is the first Spanish study on how Covid-19 infects, is transmitted and incubates with omicron, carried out by the Cantabria Public Health Observatory. Research still needs to be reviewed but it advances the reasons why the variant has generated an outbreak of infections. Almost half of those infected registered in the pandemic have occurred in the sixth wave, according to the latest data from the Ministry of Health.
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Almost two out of five close contacts of someone infected with omicron ended up being positive (39%) compared to 26% of those infected with the delta variant, explains the study, based on 622 cases detected in Cantabria in December 2021, and their 1,420 contacts , compared to 1,708 reported in November, when the dominant variant was delta.
But not only is omicron transmitted more, but its window to spread is earlier than with delta. “Half of the infections occurred before the onset of symptoms” and most between one day before the disease manifested (-1) and three days later (+3), say the researchers. In more specific terms, the delta transmission median is day 1; that of omicron, day 0.
“This would imply that the effectiveness of measures such as tracking, rapid testing or isolation would decrease significantly in the absence of preventive measures such as distance, limiting mass gatherings or social gatherings,” says the research, in which the General Director of Public Health of Cantabria, Rejhard Wallman and specialists from the Marqués de Valdecilla hospital in Santander.
In addition, once infected, there is another difference between delta and omicron. In the first case, vaccinated people transmit less of the virus. “Vaccinated cases seem to have the same transmission capacity as unvaccinated people”, concludes the study on omicron, “something that did not happen with delta, where significant differences were found in general, in homes and in workplaces” .
The isolation debate
The study also provides interesting conclusions for the debate on the duration of isolation of those infected and the open race between communities and business organizations to shorten it. The period began as 10 days and was reduced at the end of December to seven as long as there were no symptoms three days before, despite the fact that the Alerts Panel, made up of experts from the autonomous communities, asked for more time.
According to this research, those infected infected only 2% of their close contacts after the fifth day, compared to 5% of delta. The Community of Madrid and Castilla-La Mancha, in addition to the employers’ association (CEOE), have proposed a new reduction to five days of isolation, something that the Ministry of Health does not share at the moment. In this regard, the researchers point out that “it would help reduce the burden of control measures against Covid-19”.