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Central Disease Control Headquarters Deputy Director Kwon Jun-wook speaks at a briefing on Thursday. (provided by the Central Disease Control Headquarters)

After previously dismissing the prospect of herd immunity due to the Delta variant of the COVID-19 virus, South Korean disease control authorities raised the possibility once again on Thursday, predicting that it would be “possible to defeat the Delta variant even without masks once we have a complete vaccination rate of 85%.”

The remarks were meant to encourage a higher vaccination rate, but critics attacked the message as “the worst kind of communication” in that it could cause confusion with the public.

On Thursday, Central Disease Control Headquarters Deputy Director Kwon Jun-wook said, “The basic reproduction number [indicating the average number of additional people infected by any given COVID-19 patient] for the Delta variant is 5, which means that with an 85% complete vaccination rate, herd immunity would reach 80%, theoretically allowing us to overcome [the virus] without masks or restrictions on personal gatherings and business operations.”

A total of 78.3% of South Koreans had received at least one vaccine dose as of the end of the day Thursday, while 61.6% were fully vaccinated. The full vaccination rate could top 80% as early as mid- to late November as doses start to be administered to people aged 12 to 17, pregnant women, and others who have yet to be inoculated.

But with only a small percentage of the remaining unvaccinated population expressing their intent to receive a dose, it is unclear whether the 85% goal can be achieved.

At a Sept. 7 plenary meeting of the National Assembly’s Special Committee on Budget and Accounts, Korea Disease Control and Prevention Agency Commissioner Jeong Eun-kyeong predicted that herd immunity would be “difficult to achieve” because the Delta variant “is highly infectious and reduces the effectiveness of infection prevention measures.”

“We do not believe it will be possible to achieve the kind of herd immunity that completely eradicates [COVID-19] like the measles or smallpox,” she said.

At an Oct. 1 roundtable, Kim Yoon, a professor of health policy and management at Seoul National University, said, “The Delta variant is two to three times more transmissible than the initial COVID-19 virus and reduces the infection prevention effectiveness of vaccines to 79%, which means we would need a vaccination rate of 120% to achieve herd immunity.”

“That would be impossible even if the entire population were to be vaccinated. The Delta variant has rendered herd immunity impossible,” Kim concluded.

On that basis, experts predicted Kwon’s remarks could cause people to falsely believe that it will be possible to abandon masks and distancing once a certain inoculation rate is achieved.

“Herd immunity isn’t some fixed number. It refers to a situation where we are able to ease social distancing requirements as the vaccination rate increases,” said Jang Young-ook, an associate research fellow at the Korea Institute for International Economic Policy.

“For us to achieve 80% immunity with an 85% rate of complete vaccination, the vaccines would need to be 95% effective at preventing infections, but the different vaccines’ effectiveness against the Delta variant are in the range of just 60% to 70%,” he said.

“It’s the worst kind of communication that gives a false sense of hope to the public when a senior disease prevention official comes out and says we can ‘overcome the Delta variant without masks’ just a day after Prime Minister Kim Boo-kyum stressed that we ‘should not be taking our masks off for now,’” he added.

Meanwhile, the US Food and Drug Administration (FDA) indicated its lack of support for Moderna and Johnson & Johnson booster shots. South Korean disease authorities, who had been considering Johnson & Johnson alongside Pfizer and Moderna for booster shots to people who received the Johnson & Johnson vaccine, said they planned to “review things closely once there is an official announcement.”

In a document published Tuesday, the FDA suggested that booster shots of the Moderna vaccine may not be necessary, as two doses were enough to produce strong and sustained protection against COVID-19. In additional review materials published Wednesday, it failed to reach a clear conclusion on whether a Johnson & Johnson booster shot produced enough of an immunity-boosting effect, explaining that Johnson & Johnson had not provided enough evidence, the AP and other news outlets reported.

By Kim Ji-hoon and Shin Gi-sub, staff writers

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