Impact of national Covid-19 vaccination Campaign, South Korea

Synergistic effect of SARS-CoV-2 infection and COVID-19 vaccination on the risk of venous thromboembolism

BACKGROUND

Previous studies have reported a greater risk of venous thromboembolism among patients infected with SARS-CoV-2 and those who received COVID-19 vaccination. Nevertheless, there is a lack of understanding regarding the interaction effect on the risk of venous thromboembolism occurrence between SARS-CoV-2 infection and COVID-19 vaccination.

METHODS

This was a retrospective cohort study including adult patients with confirmed SARS-CoV-2 infection between October 2020 and September 2021. Patients with confirmed SARS-CoV-2 infection were selected and matched 1:1 by age and sex with individuals who were not infected during the same period. A Cox proportional hazards model was used to analyze the venous thromboembolism risk.

RESULTS

The study included 422546 individuals who were divided into four groups; the interaction group defined by having SARS-CoV-2 infection within 90 days following COVID-19 vaccination, the infection group defined by no vaccination before 90 days of SARS-CoV-2 infection, the vaccination group defined by COVID-19 vaccination without SARS-CoV-2 infection, and the reference group defined by neither COVID-19 vaccination nor SARS-CoV-2 infection. The results showed that the adjusted hazard ratio (aHR) of the interaction group was 29.71 (95% confidence interval [CI], 22.95-38.47), while the aHRs of the infection group and the vaccination group were 6.66 (95% CI, 5.18-8.58) and 2.31 (95% CI, 1.78-3.00), respectively.

CONCLUSIONS

A synergistic effect on the risk of venous thromboembolism was suggested when individuals were infected with SARS-CoV-2 within 90 days following COVID-19 vaccination.

Relative Effectiveness of the NVX-CoV2373 Vaccine Compared With the BNT162b2 Vaccine in Adolescents

This retrospective matched cohort study evaluated the efficacy of 2 doses of NVX-CoV2373 compared with that of BNT162b2 vaccines in preventing severe acute respiratory syndrome coronavirus 2 infection in adolescents. We analyzed 13-week risk differences and ratios between these 2 vaccines. The study included 465 NVX-CoV2373 and 465 BNT162b2 recipients. Throughout the follow-up period, 4.1% of NVX-CoV2373 recipients and 2.8% of BNT162b2 recipients contracted the severe acute respiratory syndrome coronavirus 2 infection. The incidence risk ratio for NVX-CoV2373 compared with that for BNT162b2 was calculated at 1.46 (95% CI 0.68-3.22; P = 0.296). While our findings suggest noninferiority between the 2 vaccines, further research is needed to comprehensively assess their effectiveness in real-world settings. Our study highlights the critical need for vigilant vaccine surveillance and monitoring efforts to ensure informed decision-making and public health protection.

Worsening of health disparities across COVID-19 pandemic stages in Korea

OBJECTIVES

With the end of the coronavirus disease 2019 (COVID-19) pandemic, the health outcomes of this disease in Korea must be examined. We aimed to investigate health outcomes and disparities linked to socioeconomic status during the COVID-19 pandemic in Korea and to identify risk factors for hospitalization and mortality.

METHODS

This nationwide retrospective study incorporated an analysis of individuals with and without COVID-19 in Korea between January 1, 2020 and December 31, 2022. The study period was divided into 4 stages. Prevalence, hospitalization, mortality, and case-fatality rates were calculated per 100,000 population. Multivariate logistic regression was performed to identify risk factors for COVID-19 hospitalization and mortality.

RESULTS

Overall, the incidence rate was 40,601 per 100,000 population, the mortality rate was 105 per 100,000 population, and the case-fatality rate was 259 per 100,000 cases. A total of 12,577,367 new cases (24.5%) were recorded in stage 3 and 8,979,635 cases (17.5%) in stage 4. Medical Aid recipients displayed the lowest 3-year cumulative incidence rate (32,737 per 100,000) but the highest hospitalization (5,663 cases per 100,000), mortality (498 per 100,000), and case-fatality (1,521 per 100,000) rates. Male sex, older age, lower economic status, non-metropolitan area of residence, high Charlson comorbidity index, and disability were associated with higher risk of hospitalization and death. Vaccination was found to reduce mortality risk.

CONCLUSIONS

As the pandemic progressed, surges were observed in incidence, hospitalization, and mortality, exacerbating disparities associated with economic status and disability. Nevertheless, Korea has maintained a low case-fatality rate across all economic groups.

Extracorporeal Membrane Oxygenation Support and Critically Ill COVID-19 Patient Outcomes: A Population-Based Cohort Study

We selected critically ill patients with coronavirus disease 2019 (COVID-19) who were receiving extracorporeal membrane oxygenation (ECMO) support and had been transferred to experienced centers. Thus, we aimed to evaluate factors that were associated with receiving ECMO support and factors that were associated with patient mortality. Using data from the National Health Insurance Service and Korea Disease Control and Prevention Agency in South Korea, adult patients admitted to an intensive care unit from October 8, 2020, to December 31, 2021, with a main diagnosis of COVID-19 were included. They were divided into two groups: ECMO group (n = 455) and non-ECMO group (n = 12,648). Receiving ECMO support was less associated with old age [odds ratio (OR), 0.95; 95% confidence interval (CI), 0.94-0.96; p  < 0.001], underlying severe disabilities (OR, 0.49; 95% CI, 0.29-0.83; p  = 0.008), and booster vaccination status (second: OR, 0.61; 95% CI, 0.39-0.94; p  = 0.024; third: OR, 0.40; 95% CI, 0.25-0.65; p  < 0.001). In addition, after adjusting for various variables, low mortality in patients with ECMO support was associated with having previously received a second booster vaccination (OR, 0.33; 95% CI, 0.14-0.77; p  = 0.010). Vaccination and booster therapy may lower the need for ECMO support and lower mortality among critically ill patients with COVID-19 with ECMO support.

Comparative Effectiveness of COVID-19 Bivalent Versus Monovalent mRNA Vaccines in the Early Stage of Bivalent Vaccination in Korea: October 2022 to January 2023

BACKGROUND

This retrospective observational matched-cohort study of 2,151,216 individuals from the Korean coronavirus disease 2019 (COVID-19) vaccine effectiveness cohort aimed to evaluate the comparative effectiveness of the COVID-19 bivalent versus monovalent vaccines in providing additional protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, critical infection, and death in Korea.

METHODS

Among individuals, those vaccinated with COVID-19 bivalent vaccines were matched in a 1:1 ratio with those who were vaccinated with monovalent vaccines (bivalent vaccines non-recipients) during the observation period. We fitted a time-dependent Cox proportional-hazards model to estimate hazard ratios (HRs) of COVID-19 outcomes for infection, critical infection, and death, and we defined vaccine effectiveness (VE) as 1-HR.

RESULTS

Compared with the bivalent vaccination group, the incidence proportions in the monovalent vaccination group were approximately three times higher for infection, nine times higher for critical infection, and 11 times higher for death. In the early stage of bivalent vaccination, relative VE of bivalent vaccine against monovalent vaccine was 42.4% against SARS-CoV-2 infection, 81.3% against critical infection, and 85.3% against death. In addition, VE against critical infection and death according to the elapsed period after bivalent vaccination was maintained at > 70%.

CONCLUSION

The bivalent booster dose provided additional protection against SARS-CoV-2 infections, critical infections, and deaths during the omicron variant phase of the COVID-19 pandemic.

Using Regional Sero-Epidemiology SARS-CoV-2 Anti-S Antibodies in the Dominican Republic to Inform Targeted Public Health Response

Incidence of COVID-19 has been associated with sociodemographic factors. We investigated variations in SARS-CoV-2 seroprevalence at sub-national levels in the Dominican Republic and assessed potential factors influencing variation in regional-level seroprevalence. Data were collected in a three-stage cross-sectional national serosurvey from June to October 2021. Seroprevalence of antibodies against the SARS-CoV-2 spike protein (anti-S) was estimated and adjusted for selection probability, age, and sex. Multilevel logistic regression was used to estimate the effect of covariates on seropositivity for anti-S and correlates of 80% protection (PT80) against symptomatic infection for the ancestral and Delta strains. A total of 6683 participants from 134 clusters in all 10 regions were enrolled. Anti-S, PT80 for the ancestral and Delta strains odds ratio varied across regions, Enriquillo presented significant higher odds for all outcomes compared with Yuma. Compared to being unvaccinated, receiving ≥2 doses of COVID-19 vaccine was associated with a significantly higher odds of anti-S positivity (OR 85.94, [10.95-674.33]) and PT80 for the ancestral (OR 4.78, [2.15-10.62]) and Delta strains (OR 3.08, [1.57-9.65]) nationally and also for each region. Our results can help inform regional-level public health response, such as strategies to increase vaccination coverage in areas with low population immunity against currently circulating strains.

Key Considerations during the Transition from the Acute Phase of the COVID-19 Pandemic: A Narrative Review

The COVID-19 pandemic has been met with an unprecedented response from the scientific community, leading to the development, investigation, and authorization of vaccines and antivirals, ultimately reducing the impact of SARS-CoV-2 on global public health. However, SARS-CoV-2 is far from being eradicated, continues to evolve, and causes substantial health and economic burdens. In this narrative review, we posit essential points on SARS-CoV-2 and its responsible management during the transition from the acute phase of the COVID-19 pandemic. As discussed, despite Omicron (sub)variant(s) causing clinically milder infections, SARS-CoV-2 is far from being a negligible pathogen. It requires continued genomic surveillance, particularly if one considers that its future (sub)lineages do not necessarily have to be milder. Antivirals and vaccines remain the essential elements in COVID-19 management. However, the former could benefit from further development and improvements in dosing, while the seasonal administration of the latter requires simplification to increase interest and tackle vaccine hesitancy. It is also essential to ensure the accessibility of COVID-19 pharmaceuticals and vaccines in low-income countries and improve the understanding of their use in the context of the long-term goals of SARS-CoV-2 management. Regardless of location, the primary role of COVID-19 awareness and education must be played by healthcare workers, who directly communicate with patients and serve as role models for healthy behaviors.

Mitigating from COVID-19 during Intercollegiate Sports Match

The coronavirus disease 2019 pandemic has posed a significant threat not only to health outcomes but also to other societal sectors, including the educational system. Apart from youth education, colleges and universities are characterized by the integration of in-depth theoretical and practical knowledge in young adulthood. Our observations in this study suggest that college fairs, sports matches, and extracurricular activities can be safely resumed when population-level immunity has reached herd protection.

Vaccine effectiveness and the epidemiological characteristics of a COVID-19 outbreak in a tertiary hospital in Republic of Korea

BACKGROUND

Healthcare facilities are high-risk sites for infection. This study analyzed the epidemiological characteristics of a coronavirus disease 2019 (COVID-19) outbreak in a tertiary hospital after COVID-19 vaccination had been introduced in Republic of Korea. Vaccine effectiveness (VE) and shared anti-infection strategies are also assessed.

METHODS

The risk levels for 4,074 contacts were evaluated. The epidemiological characteristics of confirmed cases were evaluated using the chi-square test. The "1 minus relative risk" method was used to determine VE in preventing infection, progression to severe disease, and death. In the largest affected area (the 8th floor), a separate relative risk analysis was conducted. A multivariate logistic regression analysis (with 95% confidence interval [CIs]) was used to identify transmission risk factors with a significance level <10% via the backward elimination method.

RESULTS

In total, 181 cases of COVID-19 were confirmed, with an attack rate of 4.4%. Of those cases, 12.7% progressed to severe disease, and 8.3% died. In the cohort isolation area on the 8th floor, where 79.0% of the confirmed cases occurred, the adjusted odds ratio was 6.55 (95% CI, 2.99-14.33) and 2.19 (95% CI, 1.24-3.88) for caregivers and the unvaccinated group, respectively. VE analysis revealed that 85.8% of the cases that progressed to severe disease and 78.6% of the deaths could be prevented by administering a second vaccine.

CONCLUSION

Caregiver training for infection prevention and control is necessary to reduce infection risk. Vaccination is an important intervention to reduce the risk of progression to severe disease and death.

Temporal association between the age-specific incidence of Guillain-Barré syndrome and SARS-CoV-2 vaccination in Republic of Korea: a nationwide time-series correlation study

BACKGROUND

The incidence of Guillain-Barré syndrome (GBS) changed significantly during the coronavirus disease 2019 (COVID-19) pandemic. Emerging reports suggest that viral vector-based vaccines may be associated with an elevated risk of GBS.

METHODS

In this nationwide time-series correlation study, we examined the age-specific incidence of GBS from January 2011 to August 2022, as well as data on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccinations and infections from February 2021 to August 2022. We compared the forecasted estimates of age-specific GBS incidence, using the pre-SARS-CoV-2 period as a benchmark, with the actual incidence observed during the post-vaccination period of the pandemic. Furthermore, we assessed the temporal association between GBS, SARS-CoV-2 vaccinations, and COVID-19 for different age groups.

RESULTS

In the age group of 60 and older, the rate ratio was significantly elevated during June-August and November 2021. A significant, strong positive association was observed between viral vector-based vaccines and GBS incidence trends in this age group (r=0.52, p=0.022). For the 30 to 59 years age group, the rate ratio was notably high in September 2021. A statistically significant, strong positive association was found between mRNA-based vaccines and GBS incidence in this age group (r=0.61, p=0.006).

CONCLUSION

Viral vector-based SARS-CoV-2 vaccines were found to be temporally associated with an increased risk of GBS, particularly in older adults. To minimize age-specific and biological mechanism-specific adverse events, future vaccination campaigns should adopt a more personalized approach, such as recommending homologous mRNA-based SARS-CoV-2 vaccines for older adults to reduce the heightened risk of GBS.

Estimating the number of severe COVID-19 cases and COVID-19-related deaths averted by a nationwide vaccination campaign in Republic of Korea

BACKGROUND

The Korea Disease Control and Prevention Agency promotes vaccination by regularly providing information on its benefits for reducing the severity of coronavirus disease 2019 (COVID-19). This study aimed to analyze the number of averted severe COVID-19 cases and COVID-19-related deaths by age group and quantify the impact of Republic of Korea's nationwide vaccination campaign.

METHODS

We analyzed an integrated database from the beginning of the vaccination campaign on February 26, 2021 to October 15, 2022. We estimated the cumulative number of severe cases and COVID-19-related deaths over time by comparing observed and estimated cases among unvaccinated and vaccinated groups using statistical modeling. We compared daily age-adjusted rates of severe cases and deaths in the unvaccinated group to those in the vaccinated group and calculated the susceptible population and proportion of vaccinated people by age.

RESULTS

There were 23,793 severe cases and 25,441 deaths related to COVID-19. We estimated that 119,579 (95% confidence interval [CI], 118,901-120,257) severe COVID-19 cases and 137,636 (95% CI, 136,909-138,363) COVID-19-related deaths would have occurred if vaccination had not been performed. Therefore, 95,786 (95% CI, 94,659-96,913) severe cases and 112,195 (95% CI, 110,870-113,520) deaths were prevented as a result of the vaccination campaign.

CONCLUSION

We found that, if the nationwide COVID-19 vaccination campaign had not been implemented, the number of severe cases and deaths would have been at least 4 times higher. These findings suggest that Republic of Korea's nationwide vaccination campaign reduced the number of severe cases and COVID-19 deaths.

The effect of mixed vaccination rollout strategy: A modelling study

Vaccines have measurable efficacy obtained first from vaccine trials. However, vaccine efficacy (VE) is not a static measure and long-term population studies are needed to evaluate its performance and impact. COVID-19 vaccines have been developed in record time and the currently licensed vaccines are extremely effective against severe disease with higher VE after the full immunization schedule. To assess the impact of the initial phase of the COVID-19 vaccination rollout programmes, we used an extended Susceptible - Hospitalized - Asymptomatic/mild - Recovered (SHAR) model. Vaccination models were proposed to evaluate different vaccine types: vaccine type 1 which protects against severe disease only but fails to block disease transmission, and vaccine type 2 which protects against both severe disease and infection. VE was assumed as reported by the vaccine trials incorporating the difference in efficacy between one and two doses of vaccine administration. We described the performance of the vaccine in reducing hospitalizations during a momentary scenario in the Basque Country, Spain. With a population in a mixed vaccination setting, our results have shown that reductions in hospitalized COVID-19 cases were observed five months after the vaccination rollout started, from May to June 2021. Specifically in June, a good agreement between modelling simulation and empirical data was well pronounced.

Effectiveness of Heterologous COVID-19 Vaccine Booster in Korean Elderly Population, 2022

We conducted a cohort study to assess vaccine effectiveness (VE) of coronavirus disease 2019 vaccine combinations on severe acute respiratory syndrome coronavirus 2 critical infection and death among elderly population in Korea. From January to August 2022, VE against death for 4 doses mRNA recipients was 96.1%, whereas 1-dose viral vector + 3-dose mRNA recipients had VE of 90.8%.

Factors Associated with Fatal COVID-19 Outcomes among People Living with HIV: A Cohort Study

BACKGROUND

People living with HIV (PLHIV) are at increased risk of COVID-19 death. However, information about whether factors related to the HIV-infection influence the COVID-19 outcome still remains conflicting.

OBJECTIVE

Here, we evaluate the risk factors for fatal COVID-19 in a cohort of PLHIV from the Moscow region, aged >18 years and diagnosed with COVID-19 between March 2020 and December 2021.

METHODS

Demographic, clinical and laboratory data were compared between different COVID-19 outcomes. To analyze the risk factors associated with COVID-19 death, we employed the logistic regression method. A total of 566 PLHIV were included in the analysis.

RESULTS

The majority of individuals, 338 (59.7%), were male; 194 (34.3%) were on antiretroviral therapy; 296 (52.3%) had a comorbidity; 174 (30.7%) of patients had drug and/or alcohol dependence; 160 (33.1%) patients had CD4 counts <200 cells/μl; 253 (51.9%) had undetectable viral load. Our analysis revealed that PLHIV >55 years old (OR, 12.88 [95% CI, 2.32-71.62]), patients with a viral load of more than 1000 copies/ml (OR, 2.45 [95%CI, 1.01-5.98]) and with CD4 counts <200 cell/μl (OR, 2.54 [95%CI, 1.02-6.28]), as well as with a history of cachexia (OR, 3.62 [95%CI, 1.26-10.39]) and pneumocystis pneumonia (OR, 2.47 [95%CI, 1.03-5.92]), and drug/alcohol dependence (OR, 2.70 [95%CI, 1.36-5.39]) were significantly more likely to die from COVID-19.

CONCLUSION

These data show that people with advanced HIV-1 infection have an increased risk of fatal COVID-19 outcomes and that there is a need to improve this population's access to health services and, hence, increase their survival rates.

COVID-19 Vaccination in Korea: Past, Present, and the Way Forward

Since its first emergence in late 2019, severe acute respiratory syndrome coronavirus-2 has claimed more than 6.5 million lives worldwide and continues to infect hundreds of thousands of people daily. To combat this once-in-a-century disaster, several vaccines have been developed at unprecedented speeds. Novel vaccine platforms (messenger ribonucleic acid vaccines and adenoviral vector vaccines) have played a major role in the current pandemic. In Korea, six vaccines, including a domestically developed recombinant vaccine, have been approved. As in other countries, vaccines have been proven to be safe and highly effective in Korea. However, rare serious adverse events and breakthrough infections have undermined public trust in the vaccines, even while the benefits of vaccination far outweigh the risks. The rise of the omicron variant and the subsequent increase in excess mortality demonstrated that while vaccines are a key component of the pandemic response, it alone can fail without non-pharmaceutical interventions like masking and social distancing. The pandemic of coronavirus disease has revealed both the strengths and weaknesses of our healthcare system and pandemic preparedness. When the next pandemic arrives, improved risk communication and vaccine development should be prioritized. To enable timely vaccine development, it is essential to make strategic and sufficient investments in vaccine research and development.

Effectiveness of Second mRNA COVID-19 Booster Vaccine in Immunocompromised Persons and Long-Term Care Facility Residents

We used a nationwide population registry in South Korea to estimate the effect of a second booster dose of mRNA COVID-19 vaccine on the risk for laboratory-confirmed SARS-CoV-2 infection, critical infection, and death in immunocompromised persons and long-term care facility (LTCF) residents. During February 16-May 7, 2022, among 972,449 eligible persons, 736,439 (75.7%) received a first booster and 236,010 (24.3%) persons received a second booster. Compared with the first booster group, at 30-53 days, the second booster recipients had vaccine effectiveness (VE) against all infections of 22.28% (95% CI 19.35%-25.11%), VE against critical infection of 56.95% (95% CI 29.99%-73.53%), and VE against death of 62.96% (95% CI 34.18%-79.15%). Our findings provide real-world evidence that a second booster dose of mRNA vaccine substantially increases protection against critical infection and death in these high-risk population groups.

Household Secondary Attack Rates of SARS-CoV-2 Omicron Variant, South Korea, February 2022

We studied the effect of booster vaccinations on reducing household transmission of SARS-CoV-2 B.1.1529 (Omicron) variant in a February 2022 sampling of contacts in South Korea. The secondary attack rate was lower for vaccinated versus unvaccinated contacts, and booster vaccination resulted in a lower incidence rate ratio.