People infected with the delta variant of the novel coronavirus may be carrying more than a thousand times more virus particles and may test positive two days earlier than those infected with the original SARS-CoV-2, according to an early new study. Although the study was not peer reviewed and only looked at a few cases in China, it may help to explain why the delta variant of the novel coronavirus is more infectious.

The delta variant has now spread to more than 100 countries and currently makes up 83% of new COVID-19 cases in the U.S., with particularly high case numbers in areas with low vaccination rates, Live Science previously reported. This variant is 60% more transmissible that the dominant strain and twice as infectious than the original SARS-CoV-2 strain.

Researchers are still not sure why delta spreads so quickly. A group of Chinese researchers studied the spread of the delta variant from May 21’s first local transmission. The authors published their findings as a preprint study on Virological on July 7.

China’s Guangdong and the other local Centers for Disease Control and Prevention performed surveillance and screening of those infected by the delta variant and close contacts from China. Daily COVID-19 polymerase chain reactions (PCR) tests were performed on close contacts of infected persons. Officials discovered 167 local infections, which could be traced back to the index case.

They compared data from these people with data from the early days of the pandemic, when the original SARS-CoV-2 was spreading in China.

The average time between a person being exposed to the virus and testing positive for PCR was 5.61 days with the original virus, and 3.71 days with the delta variant.

John Connor, a Boston University researcher in Emerging Infectious Diseases Laboratories, stated that the most striking aspect of the report is the shorter time it takes to show significant virus levels after being exposed to the delta variant. Live Science reported that this changes the “window” of when people become infectious.

“We know that individuals go through a period of latent infection after an infection. During this time, viral concentrations are too low to detect. The study’s authors stated that viral proliferation within the host will continue, eventually leading to a detectable viral load and infection. It is crucial to understand when infected people can spread viruses. This knowledge will help you design intervention strategies to stop transmission. To put it another way, contact tracing must be more efficient to stop people transmitting delta.

Researchers also measured viral loads at the time that SARS-CoV-2 was detected in PCR tests. The viral load in the delta variant infections was 1,260 times greater than the original virus infections. This indicates that the delta variant virus can reproduce in the body faster than the original.

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The authors stated that “these data highlight the fact that the delta variant may be more infectious in the early stages of the infection.” This suggests that the person could shed more virus particles, increasing the risk of transmission.

Connor said that the delta’s higher replication rate might not be enough to explain its success. He also stated that there are still many unanswered questions. He said that future research would help to determine how infectious the virus was.