SINGAPORE: While the arrival of a COVID-19 vaccine in Singapore is good news, it will probably still take months for life to return to normal as the country builds herd immunity and the effects of the vaccine are studied more, said experts.
Those who are "lucky" to be among the first to get vaccinated may be hoping to get back to a normal way of life quickly, said vice-dean of research at the National University of Singapore (NUS) Associate Professor Alex Cook.
"But I suspect that they won’t be able to avoid wearing a mask, and socialise in more than the permitted group size and so on until enough (people) have been vaccinated that we are at or close to herd immunity."
The first shipment of the vaccine developed by United States pharmaceutical giant Pfizer and German firm BioNTech arrived in Singapore on Monday (Dec 21). This was after Prime Minister Lee Hsien Loong announced last week that the Health Sciences Authority (HSA) had approved the vaccine for use here.
Other vaccinations are also expected to arrive in Singapore in the coming months, and the country " will have enough vaccines for everyone" by the third quarter of 2021 if all goes according to plan, Mr Lee said.
READ: Pfizer-BioNTech COVID-19 vaccine approved by Singapore, first shipment expected by end-December
Singapore is likely to be among the last few countries in Southeast Asia to return to normal, but this will probably be months after the last cases of COVID-19 in the world, said president of the Asia Pacific Society of Clinical Microbiology and Infection Dr Paul Tambyah.
"If, and it is a big if, the vaccine is successfully rolled out all across the world and if it works, there is a good chance that the incidence of the disease may drop dramatically worldwide and then the WHO (World Health Organization) can declare the pandemic over and we can slowly get back to normalcy," he added.
There will be "no major change" to restrictions here for months, but as more people get vaccinated throughout 2021, Singapore will approach herd immunity, allowing preventative measures to be eased, said Professor Dale Fisher, senior consultant at NUH and Chair of the WHO Global Outbreak Alert and Response Network.
And even though a vaccine has arrived in Singapore, people need to actually get the jab to be protected, said Assoc Prof Cook.
"So until enough people are vaccinated, society as a whole does not get protected."
ESTABLISHING HERD IMMUNITY
When there is a critical mass of people who have been vaccinated, measures like mask-wearing, social distancing and closed borders can be stood down as they are no longer needed to provide the social protection from mass vaccination, he added.
The objective of mass vaccination is to achieve herd immunity to protect individuals and make sure there is an insufficient number of people who remain vulnerable to infection to sustain an outbreak, said Dean of the NUS Saw Swee Hock School of Public Health Teo Yik Ying.
"If there are enough people that have been vaccinated, then even if someone is infected, the vast majority of the people that this infected person interacts with will already be vaccinated and not be infected. This is why mass vaccination with an effective and safe vaccine remains a very powerful public health measure to protect against an infectious disease," he added.
Prof Cook said: "In the early stages, those who get vaccinated will be protected and those who haven’t yet get no protection. Later on, once enough people have been vaccinated, then those who are vaccinated have direct protection and those who haven’t will receive indirect protection, because they’ll be protected by others in the population being vaccinated," he added.
But this all depends on the effectiveness of the vaccine. For example, the situation outlined assumes that the vaccine protects against infection, and not just disease, said Prof Cook.
VACCINES STILL BEING STUDIED
Experts CNA spoke to stressed that all the COVID-19 vaccines are still being studied, and there are many things that have yet to be established.
For example, experts have not yet identified the immune marker used to measure sufficient protection from COVID-19, said infectious diseases expert Dr Leong Hoe Nam.
"We aren't sure if the immunity conferred by the vaccine is long-lasting and permanent," he said, noting that it is also unclear whether repeated doses will be needed.
For the Pfizer-BioNTech vaccine, two doses are required, to be administered 21 days apart in people 16 years and above, according to the vaccination regime submitted by the two companies.
While there is evidence that that the vaccine is able to prevent disease, evidence of whether the vaccine has protection against the transmission from the person who is vaccinated to another person is also still being studied, said experts.
This means that people who receive the vaccine will be unlikely to experience the symptoms of COVID-19 infection, including severe complications, said Prof Teo.
"Like some of the responsible governments worldwide, Singapore will be performing post-vaccination monitoring, and by doing so, we will be able to modify our public health management measures accordingly, based on the extent of protection that vaccination offers," he added.
READ: Early data show two doses of Oxford-AstraZeneca COVID-19 vaccine provoked good immune response
The worst-case scenario is that the vaccines only prevent disease caused by COVID-19, but not infection, said Prof Cook.
"In that case, if transmission still happens, then we won’t get to herd immunity through vaccination and no protection will be afforded to those as-yet unvaccinated," he added.
"That would mean instead of a 90 per cent target vaccine coverage, we’d need everyone who can be vaccinated to do so. It’s actually not that bad an outcome, as we were aiming for most people to be vaccinated anyway."
It is unclear if the vaccines prevent transmission from asymptomatic cases, because the data so far is from people who developed symptoms from COVID-19, said Prof Fisher.
"There are still things we don’t know. How well will it work in the elderly and immune-suppressed? How long will the effect persist for or will it wear off and require a booster?" he added.
READ: COVID-19: Social gatherings of up to 8 people allowed from Dec 28, further reopening of activities in Phase 3
WHAT IS THE CRITICAL MASS THAT NEEDS TO BE VACCINATED?
The critical mass, or the number of people who need to be vaccinated to prevent further spread of COVID-19 in the community also depends on the effectiveness of the vaccine, experts told CNA.
While about two-thirds of the population is usually quoted, Dr Leong said he has "greater expectations" because the coronavirus is easily transmissible and presents asymptomatically.
A vaccination rate of 75 per cent may possibly block the transmission of COVID-19 in the community, he added.
Prof Fisher noted that 70 per cent is a "commonly used number". This means that if the vaccine is 90 per cent effective, 80 per cent of Singaporeans will need to be vaccinated, he said, adding that even more than 80 per cent would be safer as COVID-19 is "very contagious".
The number may even be lower than what is predicted, as not much is known about the cross-protection from other related viruses, said Dr Tambyah.
"For example, the low incidence in Africa despite lots of surveillance suggests that there may be some immune factors that we do not understand – similarly for the low incidence of disease in children unlike influenza or other respiratory viruses," he added.
The ideal coverage of the vaccine depends on the reproduction number of the virus in the absence of control in Singapore, said Prof Cook.
"We don't actually know what this is, because throughout the pandemic we have been controlling the spread," he added.
If one person develops a COVID-19 infection and passes it on to two others, this refers to a reproduction number of 2.
With a reproduction number of 2, 50 per cent of the population needs to be protected, which means 55 to 60 per cent need to be vaccinated based on the vaccine efficacy from trials, Prof Cook said.
If the reproduction number is 3, then 66 per cent of the population needs to be protected, and so 75 per cent to 80 per cent need to be vaccinated.
"Given the need to be conservative, I would imagine MOH aiming higher, maybe even 90 per cent, but I think some of the impacts of herd immunity will start to be felt at a lower coverage," he added.
Even though a critical mass is important for the vaccine to have any effect in preventing the spread of COVID-19 in Singapore, experts CNA spoke to all agreed that making the vaccine voluntary was the right decision.
"I think that if the vaccine works, people will be lining up to get it and there is currently no good reason to make it mandatory. It should be encouraged in certain populations such as those caring for the elderly but for the rest, persuasion will be more effective and help build trust and confidence," said Prof Tambyah.
Adding that the decision to make the vaccine voluntary was "responsible and respectful", Prof Teo said: "A responsible government will want to make sure that it provides all opportunities to protect its people.
"This is precisely why Singapore has acquired sufficient supply of vaccine to inoculate everyone citizen and long-term pass holder in Singapore. However, there will be some people in the population that may not wish to take up the offer of a free vaccination, and there may be many reasons why this can happen."
Rather than making the vaccine compulsory, it is important that the "vast majority" take it, said Prof Fisher.
"It is much better to allow people to do this voluntarily and it's our role to make people understand the science and have all their questions answered. Some will take it up early and no doubt some will need some time to understand and be comfortable," he added.
"The fact is that the important questions are answered now. Vaccine side effects occur in the early post-vaccination period so we know enough now to have confidence. Plus we know it works, at least in the short term. There is really no reason to not take the vaccine with our current knowledge."