SINGAPORE - New variants of the virus that causes Covid-19 have recently caused some concern that they may evade the immune response induced by existing vaccines, but there is no evidence yet of this occurring, said experts here, urging people not to hesitate over getting vaccinated.

"Existing vaccines work against the virus variants circulating in the community, so people should continue to step up to receive the vaccine," said Professor Benjamin Seet, deputy group chief executive for education and research at the National Healthcare Group and a member of the expert committee on Covid-19 vaccination.

"The more people who are vaccinated, the more who will be protected against current variants and, likely, new variants as well."

Sars-CoV-2, the virus that causes Covid-19, began mutating soon after it was discovered. The new variants that were first identified in Britain (B117), Brazil (P1) and South Africa (B1351) appear to be more contagious. In pre-emptive moves, vaccine developers are preparing to modify their vaccines against these variants.

"There is no immediate cause for concern, as these new variants have not been shown to cause more serious illness," said Prof Seet, who chairs an expert panel that looks at the science and technical aspects of Covid vaccines to determine which ones are better.

"If the virus continues to mutate, there may be a need for second-generation vaccines or a booster. But it is really too early to tell."

For now, existing vaccines are not affected but many people remain hesitant about taking them.

"Quite a number of people have asked me about the speed of development of the vaccines, and they are concerned that what normally takes five to 10 years is now compressed into a matter of months," said Prof Seet.

But the unprecedented spread of the disease has led to an unprecedented response.

"For a typical infectious disease, we'll be lucky to have a handful of companies trying to make a vaccine for it. What's happening now is that there are more than 200 efforts globally," said Prof Seet.

The amount of funds that has poured into Covid-19 vaccine development is also "totally unprecedented in history".

Associate Professor Lim Poh Lian, who is also a member of the expert committee on Covid-19 vaccination, noted that "governments around the world were providing funding to the pharmaceutical companies to reduce some of that commercial risk because if you make three movies all at one shot, and they all bomb, then you've just lost three times as much money".

Clinical trials could also be sped up because of the widespread outbreaks in many countries.

Prof Lim said: "With Covid-19, there were enough people willing to volunteer because they could see the pandemic happening.

"And it was actually gaining transmission in the community, so you can see whether the vaccine works or not."

Changes in the regulatory review process also helped.

Traditionally, vaccine companies would submit a vaccine for review only when all the data is in, but they are now providing their data to the authorities on a rolling basis, as it comes in.

Prof Seet said that the groundwork to get Covid-19 vaccines into Singapore started last April, when experts started looking at "seven or eight different types of vaccine technologies".

As more information came in, they whittled down the list.

"We decided on a mix of traditional vaccine technologies - inactivated vaccines, protein subunits, as well as the new technologies involving RNA and viral vectors," said Prof Seet.

"We favoured certain ones based on strength and science, how well designed the studies were, as well as the track records of the company."

The technology types that were eliminated early were DNA vaccines (because very little is known about them) and the live attenuated vaccines (because these could potentially worsen the disease if they are not properly manufactured or engineered), said Prof Seet.

The Pfizer-BioNTech vaccine that is currently used here, the Moderna vaccine that Singapore has signed advance purchase agreements for and the Arcturus-Duke-NUS vaccine that is being trialled here are messenger RNA (mRNA) vaccines, which carry instructions for cells to make a protein that triggers an immune response.

"They are not entirely new because there are ongoing clinical trials for this vaccine for other viral diseases. It's just that the companies very quickly adapted what they were doing for other diseases for Covid-19," said Prof Seet.

They were viewed favourably also because they could be produced in large quantities early on, among other reasons, he said.

And when clinical trials started, the mRNA vaccines as well as the viral vector vaccines were progressing very rapidly, making them very attractive bets.

"The Pfizer vaccine, the one we have today, works extremely well. It's an A-star based on Singapore's PSLE standards," said Prof Seet. "We are actually quite impressed with the safety profile."

Still, Prof Lim, who runs a travel clinic that gives out about 50,000 doses of vaccines every year, acknowledges the nervousness that accompanies new things.

The head of the Travellers' Health and Vaccination Clinic at Tan Tock Seng Hospital let on that she was very nervous about being among the first 40 National Centre for Infectious Diseases (NCID) staff here to take the first dose of the Pfizer-BioNTech vaccine at the end of last year.

Prof Lim, who is also the director of the high-level isolation unit at NCID, said the Pfizer-BioNTech vaccine's phase three studies found that 14 per cent of the volunteers had developed a fever after the jab, and hence, there was a chance that at least five of the 40 would develop a fever after the jab.

But none of them developed a fever after that, though about 40 per cent of the group experienced a sore arm and some had other side effects like fatigue, lasting around 24 to 36 hours, said Prof Lim.

These side effects are a sign that the body is mounting an immune response to the vaccine.

Long-term effects of the vaccine are rare, she said.

Instead of weighing between getting a vaccine and not getting one, people should consider the risk of getting a vaccine against the risk of getting the disease, she said.

"We know that it's a matter of time before more and more people get infected, because the virus itself has asymptomatic infection."