Dr's Casebook: Why the coronavirus Delta variant spreads so quickly

Everyone is now aware that the coronavirus has several variants and that currently the Delta variant, which first appeared in India late last year, has spread around the world and is now the predominant strain in this country.

Saturday, 31st July 2021, 4:45 pm
It now seems that the Delta variant is probably more than twice as transmissible as the original strain of Covid. Photo: Getty Images

Why it should have become so successful in doing this is an important question.

It now seems that the Delta variant is probably more than twice as transmissible as the original strain of Covid.

This is the finding of researchers in China who tracked and studied the effects of the virus on 62 people who had been quarantined after contracting the Delta variant. They tested them for viral load.

Essentially, this is the total amount of a virus a person has inside of them.

Viral load usually refers to the amount of measurable virus in a standard volume of material, such as blood or plasma.

This was measured on a daily basis throughout the course of their infection.

Thus, they could chart how it changed over that period of time.

They then compared their results with those of 63 people who had contracted the original Covid strain in 2020 and who had been studied at the start of the pandemic.

They found some highly significant differences.

Firstly, they found that the virus was first detectable in people with the Delta variant four days after exposure.

In people infected with the first strain, symptoms did not appear until on average six days after exposure.

This indicates that the Delta variant replicates much faster inside the body.

Secondly, people infected with the Delta variant had viral loads more than a thousand times higher than those in people infected with the original Covid strain.

It is this combination of a high number of viruses and a shorter incubation period that seems to be why the Delta has become much more transmissible.

Importantly, people infected with the Delta may be spreading the virus before they are symptomatic.

This makes the importance of quarantining immediately after coming into contact with someone diagnosed with Covid so important.

People who are fully vaccinated can still get infected with the Delta variant but all the data suggests that they are mainly protected from getting severely sick or dying. So yet again, I urge everyone to get fully vaccinated when they are able to.