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Study suggests people infected with Delta variant spread COVID-19 before symptoms appear

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Lara Adejoro

A new study suggests that people infected with the Delta variant of SARS-CoV-2 are more likely to spread the virus before developing symptoms than people infected with earlier versions.

The study led by researchers from the Guangdong Provincial Center for Disease Control and Prevention, Guangdong province, China; WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health; Foshan Center for Disease Control and Prevention, Guangdong province, China; was titled: ‘Transmission dynamics and epidemiological characteristics of Delta variant infections in China.’

The researchers collected data on confirmed cases and their close contacts from the outbreak that occurred in Guangdong, China in May-June 2021. 

The study showed that patients infected with the Delta variant had more rapid symptom onset. 

“The shorter and time-varying serial interval should be accounted for in the estimation of reproductive numbers. The higher viral load and higher risk of pre-symptomatic transmission indicated the challenges in the control of infections with the Delta variant,” they said.

According to the nature, an epidemiologist at the University of Hong Kong and a co-author of the study, Benjamin Cowling says “It is just tougher to stop”.

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.

The researchers also calculated Delta’s ‘basic reproduction number’, or R0, which is the average number of people to whom every infected person will spread the virus in a susceptible population. 

They estimated that Delta has an R0 of 6.4, which is much higher than the R0 of 2–4 estimated for the original version of SARS-CoV-2, says Marm Kilpatrick, an infectious-disease researcher at the University of California, Santa Cruz. “Delta moves a bit faster, but is much more transmissible.”

As reported by Nature, 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 per cent less likely than unvaccinated individuals to infect someone else, although the estimate was based on very small sample size. 

Commenting on the study, Ondo State Epidemiologist, Dr. Stephen Fagbemi said people infected with the Delta variant of SARS-CoV-2 may be more likely to spread the virus before developing symptoms than are people infected with an earlier version 

“We know that the delta variant spreads almost 200 times faster than the earlier versions; so it’s more likely to be true.

“The study is supporting the fact that the variant spreads very fast. You will notice that we are recording more deaths now unlike the second wave.

“It is now left for people to believe that the virus is real or not,” he said.

He advocated that offices should ensure that their staff wears a face mask and adhere to the non-pharmaceutical guidelines against the virus.

“I hope Nigerians will not learn when it is too late, I hope we don’t learn when many lives would have been lost to the virus,” Fagbemi said.

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