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80% of population must get vaccinated for herd immunity: Expert

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At least 80 per cent of Singapore's population would have to be vaccinated to achieve herd immunity against Covid-19, said the Health Ministry's chief health scientist, Professor Tan Chorh Chuan.

Assuming the efficacy of a Covid-19 vaccine is 90 per cent, vaccinating 80 per cent of the population would mean about 72 per cent of them would become protected, he told The Straits Times on Wednesday.

Prof Tan strongly encourages everyone who is suitable to get the vaccination because this would protect them and their loved ones with whom they are in close contact, and reduce the likelihood of spread in Singapore.

"Where most of a population has 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," he said.

"The estimates for herd immunity vary generally around 60 per cent to 70 per cent of the population, but a vaccine coverage of at least 80 per cent would be prudent."


On Monday, Prime Minister Lee Hsien Loong disclosed Singapore's Covid-19 vaccination plan in a televised address, and said the first shipment of Covid-19 vaccines by US pharmaceutical giant Pfizer and its German partner BioNTech would arrive before the close of the year.

Priority for the first shipments will be given to healthcare workers, those on the front-lines, as well as elderly and vulnerable patients. But there will be enough vaccines for everyone by the third quarter of next year, said PM Lee.

Achieving herd immunity against Covid-19 helps protect those who cannot be vaccinated because of their age or their medical conditions.

These include people with a history of anaphylaxis, or severe allergic reactions, who should not receive the Covid-19 vaccine at this time, said Prof Tan, as well as pregnant women.

Singapore also has advance purchase agreements for other vaccines, including those by Moderna in the US and Sinovac in China.