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Herd immunity now unachievable: microbiologists

2021-08-25 HKT 12:06
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  • Yuen Kwok-yung says Hong Kong should stick to its zero-Covid strategy in a bid to buy time to vaccinate everyone. File Photo: RTHK
    Yuen Kwok-yung says Hong Kong should stick to its zero-Covid strategy in a bid to buy time to vaccinate everyone. File Photo: RTHK
Prominent microbiologist Yuen Kwok-yung and his team said on Wednesday that Hong Kong should maintain its zero-Covid strategy for the time being, while suggesting herd immunity is no longer achievable with the emergence of the Delta variant.

In an article published in Ming Pao, Yuen and his team from the University of Hong Kong said the threshold for herd immunity had greatly increased as the Delta variant is transmissible among vaccinated people.

They said previously, herd immunity could be achieved if 70 percent of a population were vaccinated with BioNTech jabs which have an efficacy rate of 95 percent.

The researchers said their latest calculations now showed threshold had increased to 97.4 percent.

Taking into account the use of Sinovac jabs which have a lower efficacy rate, the vaccination rate needed for herd immunity would be an unachievable 142.9 percent.

“A vaccination rate of higher than 100 per cent seems illogical, but it shows that as the virus continues to mutate and becomes more transmissible, reducing the efficacy of the vaccines, achieving herd immunity is like building a castle in the sky,” they wrote.

They wrote that the emergence of the mutant strain shows the first generation vaccines are not good enough and has disillusioned people with their dream of achieving herd immunity.

However, they said Hong Kong should stick to a zero-Covid target, with an aim not to eradicate the virus but to buy time to vaccinate everyone as quickly as possible. They urged people to take advantage of this “zero infection” window and receive the jabs to prevent serious complications and deaths.

They said different strategies are needed to tackle different phases of a pandemic, added that maintaining a zero-Covid target and “living with the virus” are not contradictory.

“Only when everyone is vaccinated we can discuss ways to live with the virus. When the vaccination rate is low, it’s difficult for us to talk about what anti-epidemic measures we should adopt in the next phase,” they wrote.

They said the vaccine could prevent complications and deaths but could not stop viral transmission, therefore, people should continue wearing face masks even when the city reaches a vaccination rate of 90 percent.