Tenforde et al discuss the report of Lin et al in which they describe a cohort study of 10.6 million people in North Carolina that attempts to disentangle effects of primary and booster vaccination from prior infection. Patient demographic characteristics, vaccination history, and SARS-CoV-2 laboratory testing were linked using statewide registries, although many baseline clinical characteristics of individuals were unavailable and outcome measures were missing in a high proportion of patients. Lin et al found that waning of booster dose vaccine effectiveness occurred over 4 to 6 months, but this may be partially due to patients with certain high-risk conditions, such as those who are significantly immunocompromised, getting third doses earlier than the general population. Among individuals who received a primary mRNA vaccine series, understanding comparability between those who received homologous and heterologous mRNA boosters would also be helpful to strengthen inference around benefits of receiving mixed vaccine products that was observed in this study.