Delta variant’s higher infectivity helps its quick spread
July 25, 2021
KARACHI: Since first appearing in India in late 2020, the Delta variant of SARS-CoV-2 has become the predominant strain in much of the world. Researchers might now know why Delta has been so successful: people infected with it produce far more virus than do those infected with the original version of SARS-CoV-2, making it very easy to spread, mentions Sara Reardon while reporting for Nature magazine published on July 23, 2021.
According to current estimates, the Delta variant could be more than twice as transmissible as the original strain of SARS-CoV-2. To find out why, epidemiologist Jing Lu at the Guangdong Provincial Center for Disease Control and Prevention in Guangzhou, China, and his colleagues tracked 62 quarantined people exposed to Covid-19 and who were some of the first people in mainland China to become infected with the new deadly strain. The team tested study participants’ ‘viral load’ — a measure of the density of viral particles in the body — daily throughout the course of infection to see how it changed over time. Researchers then compared participants’ infection patterns with those of 63 people who contracted the original SARS-CoV-2 strain in 2020. In a pre-print posted 12 July, the researchers report that Delta variant was first detectable in people four days after exposure, compared with an average of six days among people with the original strain, suggesting that Delta replicates much faster. Individuals infected with Delta also had viral loads up to 1,260 times higher than those in people infected with the original strain. The combination of a larger number of viruses and a short incubation period makes sense as an explanation for Delta’s heightened transmissibility, says epidemiologist Benjamin Cowling at the University of Hong Kong. The sheer amount of virus in the respiratory tract means that superspreading events are likely to infect even more people, and that people might even begin spreading the virus in the earlier stages