WHY DOES THE DELTA VARIANT HAVE A FAST PROPAGATION?

 

The Delta variant of the SARS-CoV-2 virus has been found to have qualities that make it more efficient in contagion and achieve faster spread than previous varieties. The viral load is approximately 1,000 times higher in people infected with the Delta variant than in those infected with the original coronavirus strain.

Since the Delta variant of SARS-CoV-2 first appeared in India in late 2020, it has become the predominant strain in much of the world. Researchers can now find out why Delta has been so successful: people infected with it produce far more viruses than people infected with other variants of SARS-CoV-2, making it very easy to spread.

According to current estimates, the Delta variant could be more than twice as transmissible as the original strain of SARS-CoV-2, which emerged in China in late 2019. To find out why,  epidemiologists are studying the effects of Delta on newly infected people. A study from China with 62 people who were quarantined after exposure to COVID-19 and that they were some of the first people in mainland China to become infected with the Delta strain.

The team assessed the "viral load" of the study participants, measured the amount of virus in a sample taken from the nostrils and compared it with the analysis of other samples taken from the original variety, every day during the course of the infection to see how it changed over time. The researchers then compared the infection patterns of the participants with those of 63 people who contracted the original strain of SARS-CoV-2 in 2020.

In a preliminary test published on July 12, researchers report that the virus was detectable in people with the Delta variant four days after exposure, in compared to an average of six days among people with the original strain, suggesting that Delta replicates much faster. People infected with Delta also had viral loads up to 1,260 times higher than those of people infected with the original strain.

The combination of a large number of viruses and a short incubation period makes sense as an explanation for Delta's high transmissibility. The large amount of virus in the respiratory tract means that superpropagation events are likely to infect even more people, and that people can begin to spread the virus after becoming infected.

And brief incubation makes contact tracing more difficult in countries like China, which systematically traces the contacts of each infected person and requires them to be quarantined.

But the exact difference in viral load between Delta and the original strain is expected to change as more scientists study the virus in various populations.

Several other questions about the Delta variant remain unanswered. It's not yet clear, for example, whether it's more likely to cause serious illness than the original strain, and how good it is at evading the immune system. Some of this information will emerge as researchers take a closer look at larger and more diverse populations of people infected with Delta and other variants.