A paper in The Lancet, published in January 2024, presents the results of a study investigating rates of “undervaccination” against COVID-19 across UK nations and the associated risks of severe COVID-19 outcomes. Undervaccination in this context is “receiving fewer than the recommended number of SARS-CoV-2 vaccine doses” and is believed to be associated with increased risk of severe outcomes such as COVID-19 hospitalisation or death. The study investigates the factors linked to undervaccination as well as the subsequent risk of severe COVID-19 outcomes in the UK.
Recommendations vs reality
The authors reflect that the UK COVID-19 vaccination programme was initiated on the 8th December 2020. By June 2022 the recommended schedule was one dose for children between the ages of 5 and 11, two for children between 12 and 15 years, three for those aged 16 to 74, and four for people aged 75 and above. Further doses were offered to population subgroups in the autumn of 2022 and spring of 2023.
The initial uptake of the first vaccine dose was high in the UK. By January 2022 “more than 90% of the UK population” above the age of 12 had received a COVID-19 vaccine.
“However, as more doses have been offered, uptake has declined.”
Uptake of a second dose is noticeably lower among “those older than 50 years, people of Black ethnicity, men, and those living in high deprivation and urban areas”. Despite this, licensed COVID-19 vaccines have been proven “causally effective against infection, hospitalisation, and death”. Furthermore, they are associated with a “reduction in adverse COVID-19 outcomes in observational epidemiological studies”.
Investigations have explored the factors influencing COVID-19 vaccine uptake and the effectiveness of recommended doses, but there is a “notable gap in our understanding” of the “characteristics and COVID-19 outcomes” of undervaccinated individuals and the links between undervaccination and severe COVID-19 outcomes.
“This knowledge is crucial to prevent exacerbation of existing inequalities and to provide insights for public health recommendations aimed at promoting vaccine uptake and improving health outcomes.”
The study
The authors drew on anonymised, harmonised electronic health record data with whole population coverage to conduct cohort studies in England, Northern Ireland, Scotland, and Wales. The cohorts comprised 58.9 million individuals in England, 1.9 million in Northern Ireland, 5.0 million in Scotland, and 2.4 million in Wales. By June 2022, the number of individuals undervaccinated were as follows:
- England – 26,985,570 (45.8%)
- Northern Ireland – 938,420 (49.8%)
- Scotland – 1,709,786 (34.2%)
- Wales – 773,850 (32.8%)
Higher chances of being undervaccinated were associated with “higher levels of deprivation, lower number of risk groups in those aged 5-74 years, non-White ethnicity, and being male in the age range 5-74″.
There were 33,885 severe COVID-19 events in England, 1,220 in Northern Ireland, 3,718 in Scotland, and 1,570 in Wales. The paper plots cumulative risk by week aggregated across the four nations and presents event counts in undervaccinated and fully vaccinated people by nation and age group.
“Vaccine deficit was associated with an elevated risk of severe COVID-19 outcomes in all groups and in all countries.”
Indeed, in an estimated counterfactual scenario in which everyone in the UK was “fully vaccinated” on 1st June 2022, there would have been an “associated reduction in severe COVID-19 outcomes by the end of the follow up”.
“There is now the need to build on this work by better understanding barriers to vaccination, particularly in the subpopulations identified as less likely to be fully vaccinated and to formulate health policy and public health interventions aiming to improve coverage.”
The authors consider the need to “tackle vaccine misinformation in a more direct fashion” and to “continue to diversify the use of champions to support public messaging”.
Future targets
Dr Andrew Freedman of the Cardiff University School of Medicine commented to Science Media Centre that the study “clearly demonstrates” the effectiveness of the vaccines in reducing the risk of severe outcomes at the time.
“As the authors point out, these findings will help identify which groups should in future be specifically targeted to maximise uptake of vaccines for COVID and other infections. This will be particularly crucial in the event of another pandemic.”
What do you think of the study and its conclusions? For more COVID-19 discussions at the Congress in Washington this April do get your tickets here or subscribe for further insights.
