A recent study found that people with a delta strain of the emerging coronavirus "Covid-19" can transmit the infection two days before symptoms appear.
The study was published in preprint in the journal Nature, and has not yet been peer-reviewed.
The study found that people infected with the delta strain are more likely to spread the virus before symptoms appear than people with previous strains.
Benjamin Cowling, an epidemiologist at the University of Hong Kong and co-author of the study, and his colleagues analyzed test data on 101 people in Guangdong, China who had a delta infection between May and June of this year, and data from those individuals' close contacts.
They found that, on average, people started showing symptoms 5.8 days after infection with delta, and 1.8 days after their first positive viral RNA test.
That left about two days for the individuals to shed their viral RNA before they showed any sign of COVID-19.
The researchers also found that people with delta had higher concentrations of viral particles, or viral load, in their bodies than people with the original strain of coronavirus.
"Somehow the virus emerges faster and in higher amounts," Cowling says.
Presymptomatic stage
As a result, 74% of delta infections occurred during the presymptomatic phase, a higher proportion than previous strains.
This high rate helps explain how this variant was able to overcome both the virus of the original strain and other strains, says Barnaby Young, an infectious disease physician at the National Center for Infectious Diseases in Singapore, to become the dominant strain worldwide.
The researchers also calculated a "basic reproduction number" (R0) for delta, which is the average number of people to whom each infected person would spread the virus in a susceptible population.
They estimated that the baseline reproduction number for delta is 6.4, which is much higher than the reproduction number for the original strain of corona estimated at 2 to 4.
A small number of study participants experienced a "breakthrough infection" with Delta after receiving two doses of the coronavirus vaccine, but the vaccine reduced the participants' viral loads at the peak of infection.
The term "breakthrough infection" means that a person who has received a corona vaccine becomes ill.
Vaccinated individuals were 65% less likely than unvaccinated individuals to infect another person, although the estimate was based on a very small sample size.
Young says this reduction is "important and reassuring that COVID-19 vaccines remain effective and a vital part of our response to the pandemic."
What is a delta breed?
The World Health Organization (WHO) has classified the delta virus mutant as a cause for concern due to its high susceptibility to spread, according to UNICEF.
Once the delta mutant appeared and was identified, it was found to spread quickly and effectively among people.
As of August 10, the delta mutant has been reported in 142 countries and is expected to continue spreading.
Is the delta strain more contagious?
The answer is yes.
The Delta strain is highly contagious, about twice the capacity of previous mutant(s).
However, the same precautions taken, such as avoiding crowded places, maintaining a distance from others, and wearing masks, must be applied with the Delta mutant.
Are coronavirus vaccines effective against the Delta strain?
The answer is yes.
WHO-approved coronavirus vaccines remain highly effective in preventing severe disease symptoms and deaths, including the delta mutant.
Are children more likely to get infected with Delta strain?
The delta mutant does not specifically target children.
There are increasing rates of infection in all age groups.
However, the delta mutant is more contagious than other strains, and people who socialize with others, and those who have not been vaccinated, are more likely to be infected with the delta mutant.
What is the Delta Plus strain?
The 'delta plus' mutant contains a new mutation in the 'spike protein' that the virus uses to enter human cells.
Because it is closely related to the mutant delta, it was named "delta plus" rather than choosing another letter from the Greek alphabet.
To date, Delta Plus has been found in relatively low numbers.