Patterns and predictors of COVID-19 vaccination among young adults at 44 US sites: Secondary analysis of a randomized, controlled, open-label trial, March - December 2021

Background: The introduction of vaccines during the COVID-19 pandemic provided an opportunity to slow transmission of SARS-CoV-2, but initial uptake of COVID-19 vaccination was slow. We analyzed data from a randomized clinical trial of the mRNA-1273 vaccine (NCT04811664) to describe the patterns of uptake of COVID-19 vaccines among young adults.

Methods: The CoVPN 3006 trial randomized adults ages 18-29 from 44 sites in the United States to receive 1) immediate mRNA-1273 vaccination from the study site, or 2) standard of care, including the option to seek vaccination at any time in the future. Randomization occurred between March and November 2021, and an observational arm of adults who declined vaccination was enrolled beginning June 2021. Among participants in the standard of care (SoC) or Vaccine Declined arms, we estimated demographic, behavioral, and health history correlates of vaccination, and the four-month cumulative incidence of COVID-19 vaccination using inverse probability weighted Kaplan-Meier estimators.

Results: Among 728 SoC and 470 Vaccine Declined participants, 79% and 16% received COVID-19 vaccination, respectively. SoC and Vaccine Declined participants were more likely to seek and receive vaccination if they reported COVID-19 preventive behaviors, including wearing masks, physically distancing, and avoiding large gatherings. We identified strong predictors of vaccination in the Vaccine Declined arm, including attending class in person (adjusted risk ratio [aRR]: 0.47, 95% confidence interval [CI] 0.21, 1.03), having a COVID-19 relevant medical condition (aRR: 1.95, 95% CI: 0.89, 4.26), and avoiding large gatherings (aRR: 2.24, 95% CI: 1.18, 4.25), though low vaccination rates in this arm led to imprecise estimates.

Conclusions: Individuals who initially decline vaccination can be convinced to vaccinate, particularly if they are already practicing other forms of COVID-19 prevention. Continued outreach and education from the scientific community can combat low vaccine confidence.