Age reporting in the Brazilian COVID-19 vaccination database: What can we learn from it?

Age is a key variable for sciences and public planning. The demographic consequences of not measuring age correctly are manifold, including errors in mortality rates and population estimates, particularly at older ages. It also affects public programs because target populations depend on reliable population age distributions. In Brazil, the start of the vaccination campaign against COVID-19 marked the collection of new administrative data. Every citizen must be registered and need to show an identity document to get vaccinated. The requirement of proof-of-age documentation provides a unique opportunity for measuring the elderly population using a different database. This article examines the reliability of age distributions of men and women 80 years and older. We calculate various demographic indicators using data from the vaccination registration system and compare them to those from the target population estimates of the National Vaccination Plan, censuses, and population projections for Brazil and countries with high-quality population data. We show that requiring proof-of-age, such as in the vaccination records, increases data quality, mainly through the reduction of age heaping and age exaggeration. However, I.D. cards cannot fully solve wrong birth dates that result from weak historical registration systems. Thus, one should be careful when using estimates of the old age population living in some of the Brazilian regions, particularly the North, Northeast, and Center-West. Also, our analysis reveals a mismatch between the projected population by age, sex, and region, which guided the vaccination plan, and the number of vaccinated at ages 80 and older. The methodology developed to adjust the mortality rates used in the demographic projections is probably the main factor behind the disparities found.