The delta variant is more contagious than any previous corona mutation – most likely. Time for a detailed management report.
Alpha? Hardly anyone speaks of it anymore. Because alpha is a thing of the past in many countries. Delta is the name of the Corona variant, which is now also responsible for almost all cases in this country. Studies indicate that her viral load increases faster and is significantly higher in the body than with Alpha or the original Sars-CoV-2 (wild type). Those who have been infected with Delta are obviously more contagious – and can pass the virus on after a shorter time than with the previous variants.
Vaccination also reduces the infectiousness of the Delta variant – most likely
But does this also have an impact on the risk of transmission that comes from fully vaccinated people who have become infected? “The extent to which virus transmission is reduced varies depending on the virus variant,” writes the Robert Koch Institute (RKI). The vaccination reduces the risk of virus transmission to such an extent that vaccinated persons no longer play an important role from an epidemiological point of view, summarizes the RKI.
“I wouldn’t put my hand in the fire for it, but there are some indications that this also applies to Delta,” says molecular biologist Emanuel Wyler from the Max Delbrück Center for Molecular Medicine in the Helmholtz Association in Berlin.
Previous data only partially meaningful
However, recent data from China and Great Britain made people sit up and take notice: the viral load in unvaccinated and vaccinated people infected with Delta is similar in the first days of the disease, studies have shown. This was determined using the so-called Ct value in the PCR test. In this test, the genetic material in a sample, which is only present in small quantities, is reproduced in several runs in the laboratory.
The Ct value shows how many of the rounds are necessary until the virus genome is discovered. However, this is only used to measure the amount available, explains Wyler. “The studies did not examine whether it was also a contagious virus. But that is decisive for the question of whether someone can pass it on.”
The scientist Christian Erdmann also sees these and other limitations with regard to the informative value of the previous data on Delta. “It is fundamentally difficult to deduce the risk of transmission from the pure viral load,” says the co-founder of the think tank “RapidTests”. In the case of vaccinated people, the connection between viral load and infectivity may no longer be so strong.
Corona tests are consistently reliable
But what about the risk of transmission for people with false-negative rapid tests? Both scientists point out that, according to previous studies, these tests are on average as reliable even with Delta as with previous variants. “It can even be an advantage that the viral load is higher with Delta because you can then see better whether you have been infected,” explains Wyler.
A meta-analysis of several studies on the reliability of rapid tests some time before the spread of Delta, in which Erdmann was a co-author, had shown that an average of five to ten percent of all infections with high viral loads were not detected. This could pose a risk, especially at higher incidences. Rapid tests could also fail in some cases with the delta variant, which is often associated with higher viral loads.
“If someone with a false negative test walks around a trade fair for a few hours, the person can possibly become infectious during this time,” says Erdmann. If the virus load is high and the rapid test is false-negative, it can be the case anyway. In his opinion, mouth and nose protection should therefore be “mandatory” in closed rooms in autumn and winter. He also advocates that those who have been vaccinated and those who have recovered continue to test themselves regularly – “to protect others”.
