The genetic variation of the novel coronavirus that dominates the world today infects human cells more readily than the original that emerged in China, according to a new study published in the journal Cell on Thursday.

The lab-based research suggests this current mutation is more transmissible between people in the real world compared to the previous iteration, but this hasn't yet been proven.

"I think the data is showing that there is a single mutation that actually makes the virus be able to replicate better, and maybe have high viral loads," Anthony Fauci, the United States's top infectious disease specialist, who wasn't involved in the research, commented to Journal of the American Medical Association.

"We don't have a connection to whether an individual does worse with this or not. It just seems that the virus replicates better and may be more transmissible, but this is still at the stage of trying to confirm that," he added.

Researchers from the Los Alamos National Laboratory in New Mexico and Duke University in North Carolina partnered with the University of Sheffield's COVID-19 Genomics UK research group to analyze genome samples published on GISAID, an international resource for sharing genome sequences.

They found that the current variant, called "D614G," makes a small but potent change in the "spike" protein that protrudes from the surface of the virus, which it uses to invade and infect human cells.

The scientists first posted their paper to the medical preprint site bioRxiv in April, where it received 200,000 hits, a record.

But it was initially criticized because the scientists had not proved that the mutation itself was responsible for its domination; it could have benefitted from other factors or from chance.

The team therefore carried out additional experiments, many at the behest of the editors of Cell.

They analyzed the data of 999 British patients hospitalized with COVID-19 and observed that those with the variant had more viral particles in them, but without this changing the severity of their disease.   

Laboratory experiments meanwhile showed that the variant is three to six times more capable of infecting human cells.

"It seems likely that it's a fitter virus," said Erica Ollmann Saphire, who carried out one of the experiments at La Jolla Institute for Immunology.

- 'This variant is the pandemic' -
But everything at this stage can only be said to be "probable": in vitro experiments often do not replicate the dynamics of a pandemic.

As far as we know, although the variant circulating right now is more "infectious," it may or may not be more "transmissible" between people.

At any rate, said Nathan Grubaugh, a virologist at the Yale School of Public Health who was not part of the research: The expansion of the variant "whether through natural selection or chance, means that this variant now is the pandemic." 

Writing in a commentary piece, Grubaugh added that, for the general public, these results don't change much.

"While there are still important studies needed to determine if this will influence drug or vaccine development in any meaningful way, we don't expect that D614G will alter our control measures or make individual infections worse," he said.

"It's more of a live look into science unfolding: an interesting discovery was made that potentially touches millions of people, but we don't yet know the full scope or impact."

According to a Chinese study out in the journal Science said that test monkeys infected with the novel coronavirus responsible for the COVID-19 pandemic were protected from reinfection for up to 28 days later.

While the monkeys displayed initial immunity, it's unclear how long such immunity will last in humans - it will be necessary to wait months, or even years, to know if the millions of people infected at the start of the pandemic are protected from re-infection.

Scientists from Peking Union Medical College performed an experiment on rhesus macaques, often used because of their similarities to humans, to find out if they have a short-term immunity to the virus.

Six rhesus macaques were infected in their trachea with a dose of the SARS-CoV-2 virus. They developed mild to moderate symptoms, and took about two weeks to recover.

Twenty-eight days after the first infection, four of the six monkeys received another dose of virus, but this time, despite a brief rise in temperature, they showed no sign of reinfection, the study authors wrote.

By taking frequent samples the researchers discovered that the peak viral load was reached three days after the monkeys were infected. 

The monkeys showed a stronger immune response after the first infection, producing more so-called neutralizing antibodies which may have protected them against short-term reinfection, the scientists wrote.

More experiments are needed to see how long this immune defence remains, the authors said.