Predictors of incomplete COVID-19 vaccine schedule among adults in Scotland : two retrospective cohort analyses of the primary schedule and third dose

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Morrison, Kirsty and Cullen, Lucy and James, Allan B. and Chua, Vera and Sullivan, Christopher and Robertson, Chris and Carruthers, Jade and Wood, Rachael and Jeffrey, Karen and MacDonald, Calum and Shah, Syed Ahmar and Rudan, Igor and Simpson, Colin R. and McCowan, Colin and Vittal Katikireddi, Srinivasa and Grange, Zoe and Ritchie, Lewis and Sheikh, Aziz (2023) Predictors of incomplete COVID-19 vaccine schedule among adults in Scotland : two retrospective cohort analyses of the primary schedule and third dose. Vaccine, 41 (40). pp. 5863-5876. ISSN 1873-2518 (https://doi.org/10.1016/j.vaccine.2023.07.070)

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Abstract

Background: Vaccination continues to be the key public health measure for preventing severe COVID-19 outcomes. Certain groups may be at higher risk of incomplete vaccine schedule, which may leave them vulnerable to COVID-19 hospitalisation and death. Aim: To identify the sociodemographic and clinical predictors for not receiving a scheduled COVID-19 vaccine after previously receiving one. Methods: We conducted two retrospective cohort studies with ≥3.7 million adults aged ≥18 years in Scotland. Multivariable logistic regression was used to estimate adjusted odds ratios (aOR) of not receiving a second, and separately a third dose between December 2020 and May 2022. Independent variables included sociodemographic and clinical factors. Results: Of 3,826,797 people in the study population who received one dose, 3,732,596 (97.5%) received two doses, and 3,263,153 (86.5%) received all doses available during the study period. The most strongly associated predictors for not receiving the second dose were: being aged 18–29 (reference: 50–59 years; aOR:4.26; 95% confidence interval (CI):4.14–4.37); hospitalisation due to a potential vaccine related adverse event of special interest (AESI) (reference: not having a potential AESI, aOR:3.78; 95%CI: 3.29–4.35); and living in the most deprived quintile (reference: least deprived quintile, aOR:3.24; 95%CI: 3.16–3.32). The most strongly associated predictors for not receiving the third dose were: being 18–29 (reference: 50–59 years aOR:4.44; 95%CI: 4.38–4.49), living in the most deprived quintile (reference: least deprived quintile aOR:2.56; 95%CI: 2.53–2.59), and Black, Caribbean, or African ethnicity (reference: White ethnicity aOR:2.38; 95%CI: 2.30–2.46). Pregnancy, previous vaccination with mRNA-1273, smoking history, individual and household severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) positivity, and having an unvaccinated adult in the household were also associated with incomplete vaccine schedule. Conclusion: We observed several risk factors that predict incomplete COVID-19 vaccination schedule. Vaccination programmes must take immediate action to ensure maximum uptake, particularly for populations vulnerable to severe COVID-19 outcomes.

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