Age-specific susceptibility between Omicron-driven, Delta-driven, and Delta pre-waves in South Korea

In a recent study posted on Research Square* Preprint server, researchers have compared age-variable susceptibility to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron strain infection compared to Korean SARS-CoV-2 delta and pre-delta strains. Was evaluated.

Background

Omicron (B.1.1.529) has been reported to have higher transmission rates than previous SARS-CoV-2 strains, especially in children, increasing the number of pediatric cases of Omicron. This may be due to the priority of older people with coronavirus disease 2019 (COVID-19) vaccination and higher contact between children attending school compared to adults.

However, there is a lack of confirmatory data on the relative susceptibility to Omicron infection between individuals of various ages. The authors of this study have previously described a model for estimating age-dependent susceptibility to delta infections.

About research

In this study, researchers updated their previous model by assessing age-dependent susceptibility to Omicron infection compared to Korean delta and pre-delta infections.

Daily COVID-19 incidence and vaccination rates for age structure were obtained from the Korean Ministry of Health. Vaccination data (manufacturer and dose) were provided by the Korea Disease Control and Prevention Agency. Population data that changes with age was obtained from the Statistics Korea.

The period from January 1st to January 31st, 2022 is considered to be the Omicron dominant period (5th wave), and the period from June 27th to August 21st, 2021 is the delta dominant period (4th wave). Was considered. The predominant period (third wave) of PreDelta shares was between October 15th and December 22nd, 2020.

For the analysis of the 5-year-old age group, we used a mathematical compartment model by age group and Bayesian statistical inference to adjust data on contact patterns, vaccination status, and vaccines. Effectiveness Decrease. In addition, sensitivity analysis was performed by varying the number of contacts in school and increasing the rate of asymptomatic infections to 50% at all ages.

Model compartments were stratified by infection status (ie, exposure) [E]Sensitive [S]Infectious and asymptomatic [Iasym]Infectious and presymptomatic [Ipresym]Infectious and symptomatic treatment [Isym]And quarantine [Q]) Age zone, and time to transition to the next infection.

The proportion of asymptomatic cases by age group (ie, <4 years, 5-11 years, 12-17 years, and ≥ 18 years each) was considered baseline data for the proportion of asymptomatic cases. .. Similarly, the efficacy of the vaccine considered the upper and lower limits of the 95% confidence interval (CI) of the sensitivity analysis reported in previous studies.

Results and discussion

The proportion of SARS-CoV-2 infected cases in individuals under the age of 19 was 11.0%, 16.7, and 28.6% in wave 3 (predelta), wave 4 (delta), and wave 5 (omicron), respectively. .. The corresponding proportions of COVID-19 cases in individuals over the age of 60 were 28.5%, 10.2%, and 10.0%, respectively. In the data adjustment (older age), the corresponding proportions of COVID-19 cases in individuals under 19 years were 13.3%, 23.4%, and 36.9%, respectively.

The increase in age dependence was similar in the pre-delta (third) and delta (fourth) COVID-19 waves, whereas in the omicron (fifth) wave, an inverted bell-shaped curve was observed. , Shows a substantial difference in susceptibility to Omicron infection. It for pre-delta and delta infections among young people.

The most notable difference was observed in individuals aged 10 to 15 years, with Omicron / Predelta strain infection susceptibility being 5.28 times higher and Omicron susceptibility 2 times higher in individuals over 50 years. The fewest differences were observed in individuals over the age of 75. Similarly, the increase in omicron / delta susceptibility was highest (3.2-fold higher) in individuals aged 15-19 years and minimal in individuals aged 75 years and older (0.9-fold higher).

Vaccine efficacy, contact patterns, and asymptomatic case ratios did not change the increase in infection susceptibility before Omicron / Omicron strains, with higher values ​​for individuals younger than 19 years and pre-Delta strains. It was five times more susceptible to infection. It is three times more susceptible to delta infection.

The findings are based on a report from the US Centers for Disease Control and Prevention (CDC), which states that hospitalization rates for individuals aged 12 to 17 years at peak omicron waves are 3.5 times higher. Delta dominant period. However, increased susceptibility to infection does not always correlate with increased hospitalization rates.

Studies have shown that Omicron’s tropism shifts from the lower respiratory tract to the upper respiratory tract. This may explain that children are relatively small and immature compared to adults and are more susceptible to omicrons in the pediatric population. In addition, cases were detected during an increase in croup (acute laryngeal tracheobronchitis with a characteristic dog barking cough), a period of Omicron predominance in southern South Korea. In addition, Omicron prefers to enter host cells by endocytosis rather than via the angiotensin converting enzyme 2 (ACE2) pathway. This can further explain the increased rate of pediatric Omicron infections because children have fewer ACE receptors than adults.

Conclusion

In conclusion, based on the findings, children are more susceptible to Omicron infections than adults, and it has not yet been determined whether children’s COVID-19 vaccination is a major driver. However, it is thought to reduce the burden on COVID-19. Of SARS-CoV-2 infection.

*Important Notices

Research Square publishes unpeer-reviewed preliminary scientific reports and should not be considered definitive, guide clinical / health-related behaviors, or be treated as established information. ..