BackgroundWhile the COVID-19 pandemic may have substantially hindered the provision of routine immunisation services worldwide, we have little data on the impact of the pandemic on vaccine supply chains.MethodsWe used time-series analysis to examine global trends in vaccine sales for a total of 34 vaccines and combination vaccines using data from the IQVIA MIDAS Database between August 2014 and August 2020 across 84 countries. We grouped countries into three income-level categories, and we modelled the changes in vaccine sales from April to August 2020 versus April to August 2019 using autoregressive integrated moving average models.ResultsIn March 2020, global sales of vaccines dropped from 1211.1 per 100 000 to 806.2 per 100 000 population in April 2020, an overall decrease of 33.4%; however, the vaccine sales interruptions recovered disproportionately across economies. Between April 2020 and August 2020, we found a significant decrease of 20.6% (p<0.001) in vaccine sales across high-income countries (HICs), in contrast with a significant increase of 10.7% (p<0.001) across lower middle-income countries (LMICs), relative to the same period in 2019. From August 2014 through August 2020, monthly per capita vaccine sales across HICs remained, on average, at least four times higher than in LMICs and nearly three times higher than in upper middle-income countries.ConclusionOur study revealed the heterogeneous impact of COVID-19 on vaccine sales across economies while underlining the substantial consistent disparities in per capita vaccine sales before and during the first wave of the COVID-19 pandemic. Action to ensure equitable distribution of vaccines is needed.

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Pharmacologic therapy initiation, compliance and continuation are important components of disease management. 1 Medication nonadherence is a complex, multidimensional and multifaceted problem that contributes to suboptimal health outcomes and poses substantial challenges and financial burdens on the health care system. [2][3][4][5][6] It is estimated that as much as 50% of patients worldwide do not take their medications as pre scribed. 7 Although the causes are well understood, improving medication adherence has proven difficult. 8 Primary and second ary nonadherence are separate subsets of medication nonadherence. Unlike secondary nonadherence -which occurs when patients fill or refill the prescription but do not use it as prescribed -in primary nonadherence, patients do not fill the initial prescription or an appropriate alternative within a clinic ally acceptable time period. 9,10 Most studies of medication nonadherence that rely on claims data for dispensed prescriptions measure secondary adherence, persistence or discontinuation to pharmacother apy, but fail to account for medication initiation. 10 Research examining primary nonadherence is limited, 11 with most studies relying on selfreported measures of nonadherence to incident prescriptions via surveys, 12,13 which are hampered by methodologic limitations such as small sample sizes and self reporting bias. 14 Other studies rely on electronic prescriptions of patients discharged from hospital, 5,15,16 which constitute a subsample of patients with higher comorbidities and a distinct, shortlived patient-clinician relationship. Relatively recent shifts from paper prescriptions to electronic systems make studying primary nonadherence more feasible on larger and more rep resentative samples. 17