(AR) Changing Characteristics Over Time of Individuals Receiving COVID-19 Vaccines in Denmark: A Population-Based Descriptive Study of Vaccine Uptake

Publication Number: 1042

Background: The Danish authorities implemented a differential rollout of the COVID-19 vaccines where individuals at high risk of COVID-19 were prioritized in groups.

Objectives: We describe the temporal uptake of the COVID-19 vaccines (BNT162b2, mRNA-273, AZD1222, and Ad26.COV2.S) in Denmark and changing characteristics over time among vaccine recipients.

Methods: Using the Danish national health care registries, we identified all Danish residents ≥5 years of age who received a first dose of a COVID-19 vaccine from December 27, 2020, to January 29th, 2022. We charted the daily number of newly vaccinated individuals and the cumulative incidence over time, stratified by vaccine type, age groups, and vaccination priority groups. In addition, we described characteristics of individuals receiving the first vaccination dose over time (in subperiods: December 2020-January 2021, February-March 2021, April-May 2021, June-July 2021, August-September 2021, October-November 2021, and December 2021-January 2022) and of individuals at high risk of COVID-19.

Results: By January 29th, 2022, 88%, 86% and 64% of Danish residents ≥5 years (5,562,008) had received a first, second, and third dose, respectively, of a COVID-19 vaccine, most commonly the BNT162b2 vaccine (84% of vaccinated individuals). Fifty-one percent of those who received the first dose (n=4,892,386) were female and the median age was 47 [range 28-64]. Vaccine uptake by January 29th (first dose) increased by age ranging from 49% in 5-11-year-olds, 83% in 12-15-year-olds and up to 97% in 75-84-year-olds. Individuals prioritized for vaccination before June 2021 were older (median age 61-70 years vs. 10-35 years in later periods), more often women (50-72%), and had more comorbidities such as hypertension (22-28% vs. 0.77-2.8% in later periods), chronic lung disease (9.4-15% vs. 3.7-4.6% in later periods), and diabetes (9.3-12% vs. 0.91-2.4% in later periods).

Conclusions: The uptake of the COVID-19 vaccines is high in Denmark. We document substantial changes over time in e.g., age, sex, and medical history of COVID-19 vaccine recipients. Though these results are related to the differential rollout in the Denmark, similar findings are probable in other countries and should be considered when designing and interpreting studies on the effectiveness and safety of COVID-19 vaccines.