COVID-19 Hospitalizations Skew Younger Post-Vaccine and Post-Delta

We studied how vaccine availability and the emergence of variants of COVID-19 have affected different age groups of patients hospitalized with COVID-19. The data show that the distribution of COVID hospitalizations among different age groups has remained relatively stable since the start of the pandemic. However, there are two noteworthy trends:

After the vaccine became available, the proportion of patients in the 65+ age group decreased to make up a considerably smaller percentage of overall COVID-19 hospitalizations.
During the Delta variant surge, the percentage of hospitalizations for children that were related to COVID-19 increased.

In Figure 1, we show that patients in the 65+ age group have always made up the highest percentage of COVID-19 hospitalizations. However, since the first Emergency Use Authorization (EUA) was issued for the vaccine on December 11, 2020, the proportion of COVID-19 hospitalizations made up by this age group decreased from 57% the week of December 20, 2020 to 31% the week of July 4, 2021 then rose to 42% the week of October 17, 2021. Figure 1 also shows how these proportions changed after the CDC classified the Delta variant as a Variant of Concern (VOC) on June 15, 2021.¹

Figure 1

Percentage of COVID-19 Hospitalizations by Age Group

Figure 1. Distribution of COVID-19 hospitalizations by age group from March 2020 through October 2021. Each line represents a proportion of the weekly COVID hospitalizations. Weekly COVID hospitalizations for all age groups are represented by the gray shaded areas.

While pediatric patients represent a very small percentage of overall COVID-19 hospitalizations (just over 3% for September and October), we wanted to see whether the vaccine or Delta variant surge impacted these populations. Figure 2 shows the percentage of overall hospitalizations for each pediatric age group that were COVID-related.

Figure 2

Percentage of Hospitalizations Within Pediatric Age Groups That Are Related to COVID

Figure 2. The percentage of weekly hospitalizations across different pediatric age groups that were COVID-related from March 2020 through October 2021. For the under 1 year age group, we excluded birth admissions from the denominator. Weekly COVID hospitalizations for adult and pediatric age groups are represented by the light gray shaded areas. Weekly numbers of COVID hospitalizations for only pediatric age groups are represented by the dark gray shaded areas.

The data show that a higher percentage of hospitalizations of school-age children (5-11 and 12-15 age ranges) were COVID-related during the Delta variant surge than during previous surges of the virus.

These data come from Cosmos, a HIPAA-Limited Data Set of more than 120 million patients from 136 Epic organizations including 705 hospitals and 12,172 clinics, serving patients in all 50 states. This study was completed by two teams, composed of clinicians and data scientists, that independently acquired and analyzed data. Both teams were involved in the interpretation of results and drafting of this brief. Overall, the two teams came to similar conclusions.

References

Centers for Disease Control and Prevention. (2021, April 12). 06/15/2021: Lab Advisory: CDC Classifies SARS-CoV-2 Variant B.1.617.2 (Delta) a Variant of Concern. Centers for Disease Control and Prevention. Retrieved October 13, 2021.