Explainer: The D614G strain of the coronavirus is purportedly more infectious. Should Singaporeans be afraid?

• The D614G strain of the coronavirus is a mutation from the original strain that emerged in Wuhan
• It is the dominant strain worldwide
• Early studies have suggested that the D614G strain is more infectious, but not more deadly
• Vaccines will still remain effective against this strain

SINGAPORE — A strain of the Sars-CoV-2 coronavirus, believed to be more infectious than the original strain from Wuhan in China, has been showing up in parts of Asia.

Known as D614G, the strain was recently detected in the Philippines and Malaysia.

In a Facebook post on Sunday, Dr Noor Hisham Abdullah, director-general of Malaysia's Ministry of Health, said: "(The virus strain) was found to be 10 times likely to infect other individuals and easier to spread by super-spreader individuals."

TODAY looks at what makes this strain different from others, and whether Singaporeans should be worried.

WHAT IS THE D614G?

The D614G, also called the “G” mutation, is a variation of the original strain of the coronavirus that first emerged in Wuhan, the epicentre of the outbreak, last December.

Since then, the virus has mutated several times. A study last month by the University of Bologna in Italy found that there are at least six strains of the original Sars-CoV-2 virus which caused the Covid-19 pandemic.

Its first mutation — the S strain — appeared at the beginning of this year. The G strain emerged from mid-January onwards.

The D614G mutation is now the dominant form in the Covid-19 pandemic, making up about 70 per cent of around 50,000 genomes of the virus uploaded in a shared database carrying the mutation.

While it is most commonly found in the United States and Europe, its presence has been increasing in Asia since March.

HOW DID IT APPEAR?

Professor Gavin Smith from Duke-NUS' Emerging Infectious Diseases Programme in Singapore said that all viruses create copies of themselves during an infection.

Viruses such as the coronavirus or those that cause influenza generate mistakes during the replication process. These errors turn up as mutations, he explained.

In the case of the D614G strain, the mutation occurs when the amino acid at position 614 changes from D (aspartic acid) to G (glycine). As a result, the initial D614 variant from Wuhan becomes D614G.

WHAT MAKES IT DIFFERENT FROM OTHERS?

Research has suggested that this strain is more infectious than other strains.

In a July study published in the scientific journal Cell, Dr Bette Korber, a theoretical biologist from the Los Alamos National Laboratory in the United States, tested samples taken from patients across Europe and the US.

She and her team found that while the D614G variant was rare outside of Europe at the beginning of March, it increased in frequency worldwide by the end of the month.

“All over the world, even when local epidemics had many cases of the original form circulating, soon after the D614G variant was introduced into a region, it became the prevalent form,” Dr Korber said in a report by research website ScienceDaily.

The study found that the mutation occurs in the virus’ spike protein — the protruding portions of the coronavirus that are used to enter human cells. The strain was found to be more infectious than the D614 in cell cultures under laboratory conditions.

The team also found that patients infected with the D614G virus carried more copies of the virus than those infected with the D614 strain, possibly explaining why it is transmitted more easily.

A separate study in June by researchers from The Scripps Research Institute in the US had also found that the strain was 10 times more infectious than the original strain as its spike protein breaks less frequently. The study was published on the online research site bioRxiv and has yet to be peer-reviewed.

However, Prof Smith cautioned that these studies may not translate necessarily to what occurs in humans. Other researchers have also pointed out that these studies merely suggest but do not prove that the D614G strain is more infectious.

IS IT DEADLIER?

The study by Dr Korber also found that the strain is not deadlier compared to others. It found that hospitalisation rates were more dependent on factors such as age and gender.

Prof Smith from Duke-NUS told TODAY that there is no evidence to suggest that the D614G strain is deadlier.

He added that the strain has simply become dominant because those with the strain had entered countries where the spread of the virus was not well-controlled.

WILL IT TAKE ROOT IN SINGAPORE?

Dr Sebastian Maurer-Stroh, the deputy executive director of research at the Agency for Science, Technology and Research’s Bioinformatics Institute, said it is likely that the strain has been brought into Singapore by travellers, but current containment measures have prevented the variant from spreading here.

In an article by The Straits Times on Monday, Associate Professor Hsu Liyang, an infectious diseases specialist at the National University of Singapore’s Saw Swee Hock School of Public Health, said that the mutation has been circulating in Singapore since February, with thousands of infections here likely to be due to the D614G strain.

Prof Smith said that there is no cause for worry about the infection spreading in Singapore because there are measures in place to control its spread.

“It shouldn’t matter what virus emerges at the moment because we have safe distancing and people are keeping safe with masks. As long as people keep following such control measures, this mutation change means nothing,” Prof Smith added.

When asked if the virus could burden Singapore’s healthcare infrastructure if this strain were to spread, Prof Smith said that its transmission rate was not dependent on the genetic make-up of the virus alone but that of people’s behaviour.

“You can have the most infectious virus in the world, but if it infects a person who just watches Netflix at home, it’s not going to spread anywhere. But if it infects someone who likes to go out and meet friends, that’s when it will spread more.”

“It’s not about the nature of the virus, but the nature of the individual,” Prof Smith said.

WILL VACCINES STILL BE EFFECTIVE?

Prof Smith said that vaccines will still remain effective against this strain because they do not target part of the affected genome.

A spike protein has a “stalk” and a “head”. Antibodies from vaccines attach themselves to the head to prevent the virus from infecting human cells.

However, since the mutation for the D614G occurs on the “stalk”, this will not affect how the vaccine works, Prof Smith said.