Up to 40 Million Hidden Infections in Korea... Is 'Natural Immunity' Invincible?

US CDC "57.7% Antibody Prevalence Through Infection"
Experts "Infections in Korea Over Twice Official Counts"
Q&A on Differences Between Natural Immunity and Vaccine Immunity

On the first weekend after the social distancing measures were lifted, Banpo Hangang Park in Seoul was bustling with citizens out for an outing on the 24th. [Image source=Yonhap News]

[Asia Economy Reporter Kim Young-won] As a survey in the United States revealed that 60% of people have antibodies due to COVID-19 infection, it is suggested that the scale of natural infections in Korea may exceed the official statistics. According to the U.S. Centers for Disease Control and Prevention (CDC), a blood test conducted in February on 45,810 Americans showed that 57.7% had antibodies from infection. This is about twice the confirmed case rate of 24.2% reported by U.S. health authorities on the 28th. Experts believe that in Korea, where the highly contagious Omicron variant spread with mostly mild symptoms, about half of the population has also acquired natural immunity, similar to the U.S.

-What is the estimated scale of ‘hidden infections’ in Korea?

▲It could be up to twice the currently reported confirmed cases. In the U.S., the antibody prevalence was about 34% in December, but it rose significantly within two months, suggesting that confirmed cases in Korea also increased greatly during the Omicron wave. Since Korea’s cumulative confirmed cases are about 17 million, it is estimated that around 35 to 40 million people have actually been infected with COVID-19.

-How do natural immunity from infection and vaccine immunity differ?

▲Vaccines use only the virus’s ‘spike protein’ as an antigen, whereas immunity from infection involves the ‘whole virus’ as an antigen. Because of this, vaccines are less effective against viruses with mutations in the spike protein. On the other hand, people infected with Omicron develop antibodies against all viral proteins, which may provide protection against variants. When vaccinated individuals get breakthrough infections and acquire natural immunity as well, this is called ‘hybrid immunity,’ which is stronger than either immunity alone. However, healthy people who complete three vaccine doses form sufficient immunity and should not intentionally seek infection.

[Image source=Pixabay]

-Does natural immunity from one infection last indefinitely?

▲Like vaccine-induced immunity, natural immunity decreases over time, so it should not be assumed to last a lifetime. Just as one can catch the flu again after having it once, annual vaccinations are necessary. Further research is needed, but immunity acquired by cells through infection tends to last quite long, so natural immunity may persist longer than vaccine immunity. Also, the level of immunity varies by individual depending on symptoms experienced during infection. Those with originally weak immunity or mild symptoms tend to have fewer antibodies, while those who had severe COVID-19 tend to have higher antibody levels.

-Are symptoms milder upon reinfection with COVID-19?

▲Yes. Just as vaccines prevent severe illness and death, infection with COVID-19 acts like a live attenuated vaccine. The reason symptoms become milder after natural infection is due to cellular immunity. T cells in the body remember the virus and kill infected cells upon reinfection. As infected cells are eliminated, the virus cannot multiply, preventing the patient from becoming critically ill. If the number of people with immunity from infection increases, even if another wave occurs, the likelihood of severe cases decreases, reducing the burden on the healthcare system.

Contributors: Professor Kim Woo-joo, Department of Infectious Diseases, Korea University Guro Hospital; Professor Baek Soon-young, Emeritus Professor, Catholic University College of Medicine; Professor Chun Eun-mi, Department of Respiratory Medicine, Ewha Womans University Mokdong Hospital

This content was produced with the assistance of AI translation services.