It is a small sample size and not yet peer reviewed but found this an interesting study
People infected with the Delta variant generally do not have COVID-19 symptoms until two days after they start shedding the coronavirus.
www.nature.com
People infected with the Delta variant of SARS-CoV-2 are more likely to spread the virus before developing symptoms than are people infected with earlier versions, suggests a detailed analysis of an outbreak in Guangdong, China
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“It is just tougher to stop,” says Benjamin Cowling, an epidemiologist at the University of Hong Kong and a co-author of the study, which was posted on a preprint server on 13 August.
Cowling and his colleagues analysed exhaustive test data from 101 people in Guangdong who were infected with Delta between May and June this year, and data from those individuals’ close contacts. They found that, on average, people began having symptoms 5.8 days after infection with Delta — 1.8 days after they first tested positive for viral RNA. That left almost two days for individuals to shed viral RNA before they showed any sign of COVID-19.
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As a result, 74% of infections with Delta took place during the presymptomatic phase — a higher proportion than for previous variants. This high rate “helps explain how this variant has been able to outpace both the wild-type virus and other variants to become the dominant strain worldwide”, says Barnaby Young, an infectious-disease clinician at the National Centre for Infectious Diseases in Singapore.
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A small number of study participants experienced ‘breakthrough infections’ with Delta after receiving two doses of an inactivated-virus COVID-19 vaccine. But the vaccine reduced participants’ viral loads at the peak of infection.
Vaccinated individuals were also 65% less likely than unvaccinated individuals to
infect someone else, although the estimate was based on a very small sample size. This reduction “is significant and reassuring that COVID-19 vaccines remain effective and a vital part of our response to the pandemic”, says Young.