Seroprevalence study of SARS-CoV-2 antibodies in community based on participants in the 2020 Korea National Health and Nutrition Examination Survey (KNHANES)

Realistic Estimation of COVID-19 Infection by Seroprevalence Surveillance of SARS-CoV-2 Antibodies: An Experience From Korea Metropolitan Area From January to May 2022

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has spread globally, leading to the coronavirus disease 2019 (COVID-19) pandemic. Because a significant proportion of the COVID-19 confirmed cases were concentrated in the capital metropolitan area of South Korea, and a large proportion of the population in the area had been adequately vaccinated against COVID-19, we conducted a seroprevalence surveillance study focusing on the residents of the capital metropolitan area in South Korea.

METHODS

We used a quota-sampling method to obtain blood samples from 1,000 individuals per round, equally stratified across seven age categories and sexes and regions, from five medical institutions located within the capital metropolitan area of South Korea. During five consecutive months (rounds) between January 2022 and May 2022, a total of 5,000 samples were analyzed for anti-spike (S) and anti-nucleocapsid (N) antibodies.

RESULTS

High anti-S seropositivity was observed in all age groups, which corresponded to the vaccine coverage during the study period. Both the cumulative incidence based on polymerase chain reaction (PCR) and the estimated seroprevalence based on anti-N seropositivity increased in the fourth and fifth rounds, which corresponded to April 2022 and May 2022. Seroprevalence coincided with the cumulative incidence during the first three rounds, but exceeded from the fourth survey onwards when infection with omicron variants was increased rapidly in Korea.

CONCLUSION

Seroprevalence confirmed the number of infection cases outside of PCR testing-based surveillance. Seroepidemiological surveillance can help us understand vaccine responses and detect hidden infections, thereby providing appropriate public health guidance for achieving population-level immunity.

Protective effect of vaccination on the risk of cardiovascular disease after SARS-CoV-2 infection

OBJECTIVE

This study investigated the incidence of CVDs after COVID-19.

METHODS

Data for 2,146,130 infected people were collected, including the vaccination status. COVID-19 patients were classified according to the number of the received vaccine doses: no, first, second, and ≥ third. To evaluate the short-term risk of CVDs after infection, adjusted odds ratios (aOR) and 95% confidence intervals (CIs) were calculated by multivariable logistic regression analysis after adjustments for covariates.

RESULTS

Compared to non-infected people, aORs [95% CIs; p value] for CVDs within a month after infection were 2.80 [2.64-2.97; < 0.001] in overall infected people and 4.62 [4.23-5.05; < 0.001], 4.20 [3.45-5.11; < 0.001], 2.79 [2.55-3.05; < 0.001], and 2.07 [1.91-2.24; < 0.001] in those who were infected after receiving no, first, second, and ≥ third vaccine doses, respectively. Among participants who received second doses of vaccine prior to contracting COVID-19, the aOR in those vaccinated with only the mRNA-based vaccine (BNT162b2 and mRNA-1273; Reference) was lower than those vaccinated with the virus-derived vaccine (ChAdOx1 nCov-19 and AD26.COV2-S; aOR 1.25 [1.06-1.48; < 0.01]).

CONCLUSION

Although COVID-19 increased the CVD risk, the inverse association in the risk of CVDs according to vaccine doses was significant in a dose-response manner. Our findings suggest that ≥ second doses of the COVID-19 vaccine prevent the risk of CVDs after SARS-CoV-2 infection.

Accelerated Cognitive Function Decline in Community-Dwelling Older Adults during COVID-19 Pandemic: The Korean Frailty and Aging Cohort Study (KFACS)

This study aimed to analyze the effect of the COVID-19 pandemic on cognitive function of community-dwelling elderly individuals. Five-year (2016 to 2020) longitudinal data of the Korea Frailty and Aging Cohort Study (KFACS) were used. There were 1559 participants in 2016 and 1455 in 2017 aged 72-84 years. Follow-up was conducted at two-year intervals. We selected participants from the database of the 2017 and 2018 surveys for intergroup comparison over 2-year follow-ups. The number of study patients in the 2017-Group was 1027 and that of the 2018-Group was 879. In the intergroup comparison, the mean difference of word list memory score from 2018 to 2020 was -0.14, while that from 2017 to 2019 was 0.53. The mean difference of word list recall score from 2018 to 2020 was -0.25, while that from 2017 to 2019 was 0.03. These were significant even after adjusting confounding variables. In the intragroup comparison, the word list memory and recall scores from 2018 to 2020 were more decreased than those from 2016 to 2018. Conclusively, cognitive function of the Korean elderly cohort declined much more during the COVID-19 pandemic than before the pandemic, particularly in terms of memory and recall function.