Why COVID-19 spread continues despite 97% antibody rate among population

  • Date 2022-09-26
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This is a copyrighted material of The Korea Times.

Monday, September 26

Waining immunity, emergence of new variants remain concerns

While a recent government study found that almost all Koreans have developed antibodies against the coronavirus either by vaccination or natural infection, this finding does not mean that the population has achieved herd immunity, according to health officials.

The Korea Disease Control and Prevention Agency (KDCA) unveiled on Friday the results of its latest study, which showed that 97.4 percent of those surveyed had antibodies against the spike protein (S) of the coronavirus. The survey, co-organized with the Korea National Institute of Health (NIH), involved some 10,000 people aged five and above living in 17 cities and provinces.

A COVID-19 antibody test checks whether an individual has developed S-antibodies or nucleocapsid protein (N)-antibodies. S-antibodies are produced either through natural infection or vaccination, while the N-antibodies are formed only through natural infection.

Although the vast majority of the population has developed antibodies against the coronavirus, people should still remain vigilant and receive an updated booster shot, health officials warn.

"A positive antibody test result does not necessarily mean that the person has high immunity to the virus. We also do not know the specific antibody levels of the individuals or whether they have neutralizing antibodies," Kwon Joon-wook, director of the NIH said during a briefing. A neutralizing antibody is an antibody that actually defends cells from pathogens and infections.

He also said that the latest study has only confirmed the presence of antibodies for the original COVID-19 virus, not for the Omicron variant and its subvariants.

"Antibodies diminish over time and the possible emergence of new variants may weaken the protection offered by antibodies from a previous variant," he said, explaining that inoculation via a booster shot is essential after four months or longer following either infection or vaccination.

Kwon, however, expected that the high level of positive antibody rate among the population would help reduce the risk of falling critically ill and further bring down the fatality rate, which currently stands at 0.11 percent.

Another notable finding from the survey is the N-antibody positivity rate of 57.7 percent. The N-antibody is abundantly expressed during infections, so the figure indicates that nearly six out of 10 people have been infected with COVID-19. This figure is higher than the test-confirmed rate which stood at 38 percent as of late July. The presence of N-antibodies does not indicate immunity against reinfection, however.

The authorities presume that approximately 19.5 percent of the population, or 10 million people, have been infected without being included in the official case count. These "silent" virus carriers could have been asymptomatic, or may have avoided testing despite being ill, the KDCA said.

By age group, the percentage of these "silent infections" was the assumed to be the highest among those in their 40s and 50s: 27.62 percent and 24.83 percent, respectively.

"People in their 40s and 50s are considered the economically active population as breadwinners, with many of them assumed to be self-employed. They may have shunned getting tested on record even though they had symptoms, due to concerns about having to self-isolate," said Kim Dong-hyun, a professor of preventive medicine at Hallym University College of Medicine.

The survey results came as the government has recently lifted more COVID-19 restrictions. The outdoor mask mandate will be fully lifted from Monday, including at sports events, large rallies and concerts.

The health authorities will continue to review the gradual relaxation of the remaining measures such as the indoor mask mandate, the 7-day self-quarantine rule on virus carriers, as well as a PCR test requirement for all inbound travelers. They said they will maintain the indoor mask mandate for the time being in preparation for a possible COVID-19 resurgence during the flu season.

Meanwhile, the KDCA reported 25,792 new daily infections for Saturday, raising the aggregate total to 24,620,128.

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