J Korean Med Sci.  2022 Jan;37(3):e23. 10.3346/jkms.2022.37.e23.

Analyses of Confirmed COVID-19 Cases Among Korean Military Personnel After Mass Vaccination

• Shin DH
• Oh HS
• Jang H
• Lee S
• Choi BS
• Kim D

• KMID: 2524892
• DOI: http://doi.org/10.3346/jkms.2022.37.e23

Abstract

Background
The military was one of the first groups in Korea to complete mass vaccination against the coronavirus disease 2019 (COVID-19) due to their high vulnerability to COVID-19. To confirm the effect of mass vaccination, this study analyzed the patterns of confirmed cases within Korean military units.
Methods
From August 1 to September 15, 2021, all epidemiological data regarding confirmed COVID-19 cases in military units were reviewed. The number of confirmed cases in the units that were believed to have achieved herd immunity (i.e., ≥ 70% vaccination) was compared with the number of cases in the units that were not believed to have reached herd immunity (< 70% vaccination). Additionally, trends in the incidence rates of COVID-19 in the military and the entire Korean population were compared.
Results
By August 2021, 85.60% of military personnel were fully vaccinated. During the study period, a total of 174 COVID-19 cases were confirmed in the 39 units. More local transmission (herd immunity group vs. non-herd immunity group [%], 1 [0.91] vs. 39 [60.94]) and hospitalizations (12 [11.01] vs. 13 [27.08]) occurred in the units that were not believed to have achieved herd immunity. The percentage of fully vaccinated individuals among the confirmed COVID-19 cases increased over time, possibly due to the prevalence of the delta variant. Nevertheless, the incidence rate remained lower in military units than in the general Korean population.
Conclusion
After completing mass vaccination, the incidence rates of COVID-19 infection in the military were lower than those in the national population. New cluster infections did not occur in vaccinated units, thereby suggesting that herd immunity has been achieved in these military units. Further research is needed to determine the extent to which levels of nonpharmacological intervention can be reduced in the future.

Keyword

COVID-19; Vaccination; Korean Military; Cluster Infection; Delta Variant

Figure

• 

  Fig. 1 (A) Mass vaccination program in Korean military. (B) Classification of Korean military and COVID-19 vaccination rates.COVID-19 = coronavirus disease 2019, CO = commissioned officer, NCO = non-commissioned officer.aMilitary personnel aged 30 years or older who received the first dose with ChAdOx1 nCoV-19 were given a second dose with ChAdOx1 nCoV-19 or BNT162b2 depending on the individual's choice.bRates of fully vaccinated personnel; fully vaccinated status was defined as 2 weeks after completion of two doses of the vaccine (or one dose for Ad.26.COV2.S vaccine).cThe rate of each vaccine on August 17.

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  Fig. 2 Association between the number of confirmed COVID-19 cases and the vaccination rates of each military unita from August 1 to September 15, 2021.COVID-19 = coronavirus disease 2019.aWith the exception of two units (battalion) where cluster infections occurred, the units with confirmed COVID-19 cases were reviewed on the scale of the corps.

• 

  Fig. 3 (A) Trends of the number of confirmed COVID-19 cases by date in military units. (B) The rates of fully vaccinated patients (breakthrough infection)a among weekly confirmed COVID-19 cases in the units.COVID-19 = coronavirus disease 2019.aFully vaccinated status was defined as 2 weeks after completion of two doses of the vaccine (or one dose for Ad.26.COV2.S vaccine).

• 

  Fig. 4 The comparison of incidence rates of COVID-19 in military units and in Korean civilians.a COVID-19 = coronavirus disease 2019.aIn order to identify the effect of mass COVID-19 vaccination, the two cluster infection cases in military units were excluded. Military confirmed cases were excluded from the data of Korea.bRate of fully vaccinated people in Korea; fully vaccinated status was defined as 2 weeks after completion of two doses of the vaccine (or one dose for Ad.26.COV2.S vaccine).

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