Korea’s plan of getting to herd immunity by fall could be complicated with the country reporting the first local outbreak involving new and potentially more transmissible variants.

Korea Disease Control and Prevention Agency’s deputy director Kwon Jun-wook on Thursday warned of the possibility of the variants making the situation worse.

“From what we know, the variants are capable of spreading more easily,” he said. “If our commitment to social distancing wanes in March and April when vaccinations are underway, I worry that it could trigger another big surge in infections.”

In a previous briefing, the deputy director has called the emergence of variants “one of the greatest risks in the upcoming phase of the pandemic,” and said that their presence in communities could force Korea to “relive the nightmares of December.”

The KDCA announced a day earlier that a passenger who arrived from the United Arab Emirates in December was confirmed to have the UK variant. Ensuing investigations revealed the person had spread the infection to 38 relatives and friends while quarantining at home, all of them Syrian nationals. At least four of the secondary cases were with the variant, with analysis still pending for the rest.

On Tuesday, another passenger, also from the UAE, was confirmed with the South Africa variant. Among the 44 people who had come into close contact with the passenger, one was found to have the same variant to date.

Korea is now one of only nine countries with confirmed cases of the three variants discovered, respectively, in the UK, South Africa and Brazil, the KDCA said.

Health officials have said inoculating 70 percent of people in Korea would be sufficient for herd immunity. Na Sung-woong, a senior health official, told reporters Wednesday that “around 66.7 percent of people in Korea will need to be vaccinated for herd to be immune against COVID-19 in theory.”

But experts say these new variants may mean a higher level of herd immunity will be required than previously suggested.

“We don’t have actual data to support a particular level, though levels higher than 70 to 80 percent are more commonly being given now,” said Dr. Jerome H. Kim of the International Vaccine Institute. “With particular reference to these mutants that appear to be more transmissible, having a higher level of population immunity from vaccines would be beneficial.”

Regarding the potential of the mutant strains to affect immunization efforts, he said “the current vaccines appear to generate protective responses against these mutants,” though “the mutants do seem to be better at evading the neutralizing antibodies -- the infection-fighting proteins which are induced by vaccination.”

“You would expect that the vaccines should continue to work, but it will be important to actually generate laboratory evidence suggestive of protective antibody and clinical trial evidence of protection,” he said.

As vaccinations proceed, other steps including social distancing, face mask-wearing, contact tracing, expansive testing should continue in order to “diminish the outbreaks, and to possibly slow the development of additional mutants,” he said.

Epidemic expert Dr. Kim Woo-joo of Korea University Medical Center agreed “a higher rate of vaccination will likely be needed to reach the threshold of herd immunity.”

He said both Johnson & Johnson’s Janssen and the Novavax vaccines were shown to be weaker against the South Africa variant, according to data released by the companies last week.

Janssen said its vaccine was 57 percent effective against moderate to severe COVID-19 in South Africa -- where the majority of COVID-19 cases with the variant are -- whereas in the US it was 72 percent, in a Jan. 29 announcement on the phase 3 trial. Similarly, the Novavax vaccine, as announced by the company on Jan. 28, was 60 percent effective in its South Africa trial, compared to the UK trial’s 89.3 percent.

He said authorities “need to sequence more genomes to grasp if and how far the strains have reached the population.”

“Korea temporarily halted flights from the UK in late December, by that time it had already spread to neighboring countries in Europe,” he said, adding that tighter border controls should have been promptly instituted in places such as Japan, which has barred entry of all new arrivals, including for business travel.

“Once the variants take hold, controlling the spread will be harder, as they are known to be more transmissible. Also there will be less rationale for easing or lifting restrictions on international travel,” he said, adding the variants could soon dominate local infections.

Korea’s current travel restrictions for arriving passengers have loopholes, according to Dr. Jung Jae-hun, who is advising the government on the COVID-19 response.

“Not all international travelers are quarantined in a state-assigned facility, for instance. A significant proportion of them are quarantining at home, and as witnessed in recent cases, that has led to transmissions within households,” he said.

“Those living with other people should be provided a separate quarantine space, there should be harsher penalties for quarantine violations,” he said.

As for concerns the variants may meddle with the goal of attaining herd immunity by November, he said, “Like I’ve said, we are in a race against time.”

“We need to get down to vaccinations as soon as possible to stay ahead of the mutations that could potentially become more common.”

Korea counted 452 more cases -- 429 locally transmitted and 22 imported -- of COVID-19 on Thursday, bringing the cumulative total to 79,762. Seven more deaths were announced, with the toll now at 1,448.

By Kim Arin (arin@heraldcorp.com)