South Korea’s sluggish immunization drive, coupled with blood clot investigations into two of its purchased vaccines, is clouding the country’s prospects of achieving herd immunity before the year’s end.

So far Korea has administered about 1.34 million doses of COVID-19 vaccines since the mass vaccination campaign launched in end-February. This translates to about 27,000 shots administered a day, falling far below the government’s previously touted capacity of over 1 million.

Despite only 2 percent of the population vaccinated to date, the Ministry of Health and Welfare maintains that Korea will reach herd immunity by November.

At a closed-door briefing Thursday, a senior official at the ministry said come November, it would reach its immunity goal “without fail.”

“AstraZeneca and Novavax vaccines can be manufactured domestically, so accessing their supplies won’t be a problem,” he said. The administration was “activating all diplomatic channels” to ensure other vaccines from Pfizer, Moderna and Johnson & Johnson are delivered on time.

Dr. Paik Soon-young, a virologist at Catholic University of Korea, said the scarcity of vaccines in the country was “the biggest speed bump” right now. Korea has already used up almost 70 percent of the 3.6 million doses of AstraZeneca and Pfizer currently in stock as of Thursday.

He said in summer, when other parts of the world like the US and Europe will have completed inoculating their citizens, vaccine supply was expected to stabilize.

He said the government’s promise of a November return to normalcy was “aspirational,” and called on top authorities to communicate these uncertainties clearly and transparently to the public.

“Australia, for instance, abandoned its vaccination targets after the AstraZeneca suspension in younger populations. We need to admit herd immunity is probably unattainable at this pace,” he said. 

While vaccinations are slow to pick up, infection rates are once again on the rise amid softened social distancing. Hospital beds across the country have reached over 50 percent capacity this week, with the daily case count hovering around 700 -- a number not seen since the early days of the winter surge back in December.

Adding to the woes were more transmissible and vaccine-resistant variants circulating in the community. The number of variant cases reached 728 as of Wednesday.

“The vaccination coverage is too low for Korea to be able to defend against a new wave, especially as the rollout for older people is just getting started,” said infectious disease professor Dr. Kim Woo-joo of Korea University.

The vaccination campaign did not cover people aged 65 years and older until two weeks ago, as the AstraZeneca vaccine’s use in older groups was temporarily shelved due to insufficient data.

The first AstraZeneca batch was instead allotted only to people younger than 65 -- namely, 780,000 residents and staffers at nursing homes as well as some health care workers at non-COVID-19 hospitals. The Pfizer batch went to 58,000 front-line workers caring for patients with COVID-19.

Since age is a chief predictor of COVID-19 fatalities, primary vaccination efforts should target older people to reduce the incidence of hospitalizations and deaths, Kim said.

“From this month vaccinations are being offered to younger professions from flight attendants to teachers, but an age-based approach is probably more advisable considering the new advice on AstraZeneca shots,” he said.

Korea halted the AstraZeneca vaccine’s use in anyone under 30 after a third report emerged a week ago of a severe blood clot having developed in one of the recipients. The count of blood clot events among AstraZeneca vaccine recipients now stands at five, three of which involved previously healthy people in their 20s.

Latest available government data showed about 8.66 million more doses of AstraZeneca vaccine are set to arrive in May or June -- none of which will be given to younger people unless the age limit is lifted. But 7 million doses of the Pfizer vaccine, also expected in the next two months, are reserved for people aged 75 and up.

International Vaccine Institute’s Director General Dr. Jerome H. Kim said the benefit-risk equation would “favor the reverse” -- Pfizer in younger, and AstraZeneca in older. Still, switching up the type of vaccine given to different age groups is not a consideration at the moment, the government said.

Korea’s vaccination program depends on the success of the AstraZeneca vaccine, which makes up over 60 percent of the country’s scheduled supply for the first half of the year.

But growing evidence that suggests a link between the adenovirus technology that the vaccine uses and a rare and potentially fatal blood clot as vaccine side effect is shaking that premise. The Johnson & Johnson vaccine, which is also adenovirus-based, has come under scrutiny over similar clotting events.

Denmark stopped its AstraZeneca rollout completely on Wednesday, a move that experts say might catch on elsewhere. On the same day the European Union Commission decided not to renew its vaccine contracts with AstraZeneca and Johnson & Johnson.

Korea is expected to have access to at least some of the 6 million doses of the Johnson & Johnson vaccine it has purchased sometime between now and June. The vaccine was granted conditional approval here last week, although the latest blood clot cases could lead to restrictions similar to those affecting the AstraZeneca shots.

“There may be a spillover,” said Dr. Jean-Louis Excler, a member of the vaccine safety group within COVAX. “We may end up in a situation where more countries drop the AstraZeneca vaccine.”

The Health Ministry said in Thursday’s closed-door briefing that it would be “closely monitoring” the safety issues arising in other countries as the country continues vaccinations.

“We need to brace for the worst, and expand availability of the mRNA-vectored vaccines (from Pfizer or Moderna) that are free of the safety signals,” said Kim of Korea University.

By Kim Arin (arin@heraldcorp.com)