SINGAPORE - With over 500,000 new cases of Covid-19 being recorded worldwide every day and many millions of active cases, the coronavirus has likely undergone thousands of mutations by now, said Professor Dale Fisher, a senior infectious diseases expert at the National University Hospital.
But unlike the more infectious strains recently seen in Britain and South Africa, the vast majority of mutations do not have any effect on the activity of the virus, he said on Tuesday (Jan 19).
Speaking on The Straits Times' daily talk show The Big Story, Prof Fisher said virus mutations "can go in any of several ways".
In the case of the new strains, a change of the spike protein structure in the virus made it more transmissible by an estimated 50 per cent compared to previous known strains.
But future variations could also become less transmissible and cause either more serious or less serious disease.
"Certainly in the (case of the) Spanish Flu, the second wave was suddenly more virulent than the first one, and the flu's obviously even more mutagenic," said Prof Fisher.
"I think it really just introduces a lot of unknowns and another reason to bring these numbers down (and) under control."
Professor Alex Cook, vice-dean of research at the National University of Singapore's Saw Swee Hock School of Public Health, said the infectiousness of a virus is measured by the reproduction number R0 (R-naught), or the average number of new infections generated by each case.
The R0 of Sars-CoV-2 - the coronavirus that causes Covid-19 - is hard to calculate accurately, as it has never been left uncontrolled, noted Prof Cook. Experts, however, estimate that it is between two and 2.5.
This means each new infected person passes the virus on to two to 2.5 others on average, and those with the new strains would pass it on to even more people.
Prof Fisher noted that British health agency Public Health England conducted a study that showed patients with the older strains of Covid-19 passed the virus to about 10 per cent of their close contacts on average.
In those with the newer strain, about 15 per cent of their close contacts became infected.
A more infectious strain means a smaller "dose" of the virus will be enough to cause disease, said Prof Fisher.
"Maybe if you're being exposed to a positive case, you don't have to be exposed for as long (to catch it). Maybe it's more likely you can pick it up on your hands and infect yourself."
But existing measures such as mask wearing and hand hygiene will still be key to fighting the virus, even if they are less effective against the new strains, he said.
"It's still mostly (spread by) droplets. It can be airborne under some circumstances, or (contracted) through contact with contaminated surfaces, but the bottom line is we just have to be a lot more vigilant.
"Nothing has actually changed. It's just that, if you slip up, there's a higher likelihood of infection spreading."
Prof Cook said Singapore has so far been able to keep the R0 of the virus to one or below since it entered phase two, but if it increases to 1.5, for instance, Singapore could see the turn of exponentially growing case numbers, which would be a cause for concern.
"It would mean that we may end up with the death rate rising again. We may end up with more people going into intensive care, and it would effectively become a kind of race between a new variant of the virus, if it became established here, against our ability to deploy the vaccine en masse, at speed."
Prof Fisher said that if new strains become widespread, the formulations of Covid-19 vaccines may need to be adjusted.
While this is not yet necessary - and likely will not be necessary if Singapore can keep its new case numbers down - Prof Fisher said it remains to be seen what effects future variants of the virus might have.