SINGAPORE — Singapore’s strategy against Covid-19 does not involve the attainment of herd immunity in the population through natural spread of the infection. This would be “too big a price” to pay, an official from the Ministry of Health (MOH) said.

Speaking at a media briefing on Tuesday (May 12), Associate Professor Kenneth Mak, director of medical services at MOH, said: “If we assume that we're going to let Covid-19 spread freely in a population, we will then have to accept the cost associated with more seniors getting ill, more seniors getting complications and an undetermined number of seniors even dying from infection.”

This would also lead to a very “dangerous” situation of having a high number of Covid-19 patients potentially in Singapore’s hospitals and intensive care units.

“Even though we've taken many steps to prepare for surges to expand our capacity, it can easily be overwhelmed with a strategy of moving to herd immunity,” he added, in response to a question from the media on the proportion of the population that needs to be infected before herd immunity could be achieved.

Herd immunity refers to a situation where most of a population is immune to an infectious disease — whether through previous infections or vaccination — and this provides indirect protection to those who are not immune to the disease. In the case of Covid-19, a vaccine has yet to be developed for the Sars-CoV-2 coronavirus that causes the respiratory disease.

Associate Professor Vernon Lee, director of communicable diseases at MOH, said experts believe that about 60 to 80 per cent of the population need to be immune or previously infected and recovered, before herd immunity is achieved.

That is a “very large number”, he said.

Referring to studies of countries with large numbers of infections, Dr Lee said that serological testing found a low percentage of people who tested positive, way below the threshold required for herd immunity.

Assoc Prof Mak pointed out that this was a reason why the United Kingdom toyed with the herd immunity strategy but decided in the end that “the cost was too big, too painful for them to pay as well”.

He noted that Sweden is perhaps the only country “closest to” trying to achieve herd immunity. “But even then if you look at their mortality rates… (Sweden’s death toll) is still in the thousands,” he said.

As of Monday evening, Sweden has recorded 3,256 deaths. 

With good containment, Singapore will not reach a situation where herd immunity is achieved unless a vaccine is developed, Assoc Prof Mak reiterated.

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