Published online Mar 17, 2023.
https://doi.org/10.3346/jkms.2023.38.e100
The Crucial Role of COVID-19 Vaccination in Preventing Severe Illness and Death: Evidence From a Korean Perspective
Vaccination has played a crucial role in the fight against the COVID-19 pandemic, and numerous studies have confirmed its effectiveness. While the effectiveness of vaccination in preventing symptomatic infections varies depending on the type and timing of SARS-CoV-2 variants, its ability to prevent severe illnesses and deaths has been consistently demonstrated. For example, the estimated vaccine effectiveness (VE) of ChAdOx1 against symptomatic omicron infection after the second dose was 36% for 7–59 days and it decreased to 1% after ≥ 180; however, it increased to 61% ≥ 7 days after the third dose. In addition, the third dose was associated with a high estimated VE against severe omicron outcomes (95%; 95% confidence interval, 87–98%).1 In another study, the 4-dose VE for mRNA-1273 against BA.2, BA.2.12.1, and BA.4 infections ranged as 64.3–75.7%, and it declined 14-30 days after the fourth dose against BA.5, finally disappearing after ≥ 90 days for all subvariants. The 3-dose VE against hospitalization for BA.1, BA.2, and BA.4/BA.5 was 97.5%, 82.0%, and 72.4%, respectively; the 4-dose VE against hospitalization for BA.4/BA.5 was 88.5%.2
Fig. 1 provides a clear demonstration of the efficacy of vaccination in preventing severe illnesses and deaths. When examining the 7-day moving average of confirmed COVID-19 cases and deaths in Korea, it was apparent that the number of deaths significantly fluctuated before January 2022, while the curve for confirmed cases remained relatively stable. In contrast, during 2022, the epidemic scale increased more than tenfold, yet the number of deaths did not change significantly. This phenomenon serves as indirect evidence of the number of lives saved by vaccination.
Fig. 1
Daily new COVID-19 cases, deaths (7-day rolling average) and cumulative COVID-19 vaccination doses administered per 100 people. Note that vaccination doses administered per 100 people is counted as a single dose, and may not equal the total number of people vaccinated, depending on the specific dose regime. Data available at: kdca.go.kr.
A recent study by researchers at the Korea Disease Control and Prevention Agency (KDCA) again proved the effectiveness of vaccination in preventing severe illnesses and deaths, suggesting that the odds ratio of severe illness and death in those vaccinated with three doses was < 0.1 compared with those in the unvaccinated control group.3 These findings highlight the critical role of vaccination in overcoming the COVID-19 pandemic.
However, the timing of the study publication is an issue that future studies should address. Although several small-scale domestic and international studies have reported encouraging results on the effectiveness of the vaccine in preventing severe illnesses and deaths since the first half of 2022,4 the announcement of this large-scale study using Korea's representative database was made after the implementation of bivalent vaccinations and the conclusion of monovalent vaccinations. It is important to prioritize timely reporting to ensure that research findings are available as soon as possible.
Second, the measurement of vaccine effectiveness needs to be more clearly defined epidemiologically. While the effectiveness of a vaccine is often expressed as a simplified 1-risk or 1-odds ratio, this does not account for the emergence of new mutations or the decline in immunity over time. Therefore, it is essential to interpret vaccine effectiveness according to the flow of time and the context of policy and to communicate this effectively to the public. Timely reporting and mid- to long-term follow-up are necessary to understand the effectiveness of vaccines.
Third, leveraging Korea's large-scale administrative, confirmation, and health insurance claim data is crucial for research, and there is a need to explore and maximize the potential of this data for various applications. In Korea, various data sources are being integrated for the entire population, and in the context of the COVID-19 crisis, the K-COV-N cohort has been made available to researchers since the second half of 2022.5 To enhance the usefulness of these databases, it is essential to ensure they are more accessible, transparent, and updated in a timely manner. Government authorities should prioritize efforts to facilitate research and improve the effectiveness of policies aimed at fighting the pandemic.
In conclusion, vaccination remains the most crucial solution to dealing with infectious diseases, and it is the responsibility of policymakers and researchers to provide clear evidence of its effectiveness and safety. Although the KDCA study results are encouraging, it is important to continue research and report findings in a timely manner to enhance our understanding of vaccine effectiveness and optimize its usage in the ongoing battle against COVID-19.
Disclosure:The author has no potential conflicts of interest to disclose.
References
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KDCA. Opening big data for effective response to COVID-19. [Updated 2022]. [Accessed February 25, 2023].https://www.kdca.go.kr/board/board.es?mid=a20501010000&bid=0015&list_
no=719138&cg_ code=&act=view&nPage=2.
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