Experts believe two-thirds of S’pore population must be vaccinated to achieve herd immunity — but netizens concerned about “unknown” side effects

Several infectious diseases experts believed that at least two-thirds, or 80 per cent of Singapore’s population, would need to receive COVID-19 vaccinations in order for the community to achieve herd immunity against the virus.

This came after Prime Minister Lee Hsien Loong’s announcement on 14 December that the Pfizer-BioNTech COVID-19 vaccine has been approved for pandemic use by Singapore’s Health Sciences Authority and is expected to arrive by the end of December.

“First priority will be given to those who are at greatest risk – healthcare workers and frontline personnel, as well as the elderly and vulnerable,” said PM Lee in a televised address.

HSA also released a statement indicating that the vaccine demonstrated a high degree of efficacy — of 95 per cent.

Professor Ooi Eng Eong, deputy director of the emerging infectious diseases programme at the Duke-NUS Medical School, told TODAY on Thursday (17 December) that having immunity in two-thirds of the population is enough to protect the remaining population from the virus.

However, this is only possible if the vaccines are able to induce “sterilising immunity”, said Prof Ooi.

“[This] two-thirds ratio refers to herd immunity. Current trials have not been able to ascertain if either Pfizer-BioNTech’s or Moderna’s vaccine can also effectively prevent infection,” he noted.

Professor Eric Finkelstein, also from the Duke-NUS Medical School, emphasised the uptake of the vaccine is important.

“If uptake is well below that, then COVID-19 is likely to [continue] proliferating in the community,” he noted.

The Health Ministry’s chief health scientist Professor Tan Chorh Chuan told ST that while the estimates for herd immunity may vary — generally around 60 to 70 per cent of the population — he believes that “a vaccine coverage of at least 80 per cent would be prudent”.

“Where most of a population have immunity to the virus, this ‘herd immunity’ indirectly reduces the risk of infection for those who are not immune to it, thereby limiting infection clusters,” said Prof Tan.

He noted that achieving herd immunity against COVID-19 can help to protect those who cannot be vaccinated –- particularly pregnant women, people with compromised immune systems or certain chronic medical conditions, those under the age of 16, and people with a history of anaphylaxis.

“However, it is still not known if the vaccine also reduces or blocks viral transmission, although this was found in the animal studies,” Prof Tan said to ST.

“We expect that more clinical data on this important issue will become available later,” he added.

According to Dr Ling Li Min, a senior consultant at Rophi Clinic, sterilising community will mean that the vaccine can prevent the asymptomatic spread of the virus, which in turn would be able to reduce the risk of the virus transmission.

Dr Ling explained that the available vaccine primarily protects the lungs rather than the nasal area –- which is one of the channels for the virus to be transmitted to others.

“Although the current vaccine candidates have demonstrated the ability to reduce symptoms and the number of viruses in the lower respiratory tract, there is as yet no evidence of sterilising immunity in the upper respiratory tract,” she told TODAY.

While medical experts expressed confidence regarding HSA’s approval of the Pfizer-BioNTech vaccine in Singapore, they noted that the main goal of a vaccination programme is to protect the individual from the virus, without necessarily achieving sterilising immunity.

“Without sterilising immunity, more people would need to be vaccinated against COVID-19 in order to prevent another COVID-19 outbreak from re-emerging in Singapore,” said Prof Ooi.

Netizens voiced concerns about “unknown” side effects of the vaccine

Penning their thoughts under the comment section of TODAY’s and The Straits Times’ Facebook posts, many netizens voiced their concerns on the “unknown” implications and side effects of the vaccine, saying that people should not be forced to take the vaccine unless it is proven to be safe.

Some netizens suggested the government to provide assurance to the public via financial compensation should things go wrong after vaccination.

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