Pneumococcal vaccine coverage among individuals aged 18 to 64 years old with underlying medical conditions in the UK: a retrospective database analysis

Pneumococcal disease, caused by the gram-positive bacterium S. pneumoniae, is a major cause of invasive pneumococcal disease (IPD) and non-invasive pneumococcal diseases such as community-acquired pneumonia (CAP) and acute otitis media [1, 2]. IPD is of significant public health concern due to high morbidity and mortality globally, especially in the very young, the elderly and individuals with underlying medical conditions [3]. Patients with chronic and immunocompromising conditions have been shown to have substantially increased rates and costs of treatment for IPD and all-cause pneumonia (ACP) when compared with those of healthy counterparts. In 2017, the European Centre for Disease Prevention and Control (ECDC) received 23,886 notifications from 29 countries, of which 6333 cases (26.5%) were reported by the United Kingdom (UK). Furthermore, an estimated 1548 deaths due to IPD occurred within the European Union (EU) in 2017, of which 1018 were reported by the UK [4]. However, a number of countries did not report epidemiological data, and deaths reported may therefore be an underestimation [4]. The addition of influenza vaccine prior to influenza season has been shown to reduce the risk of severe courses of pneumonia, resulting in improved long-term survival [5]. However, the extent to which influenza vaccination may affect the rate of pneumococcal vaccination is unknown. In the UK, total annual healthcare costs related to pneumococcal disease are estimated to be greater than £1 billion [6]. Hospitalisations are an important contributor to this cost, with an estimated cost per episode of £4865 (patients aged 65 years) [7].

Individuals with underlying medical conditions have been targeted for pneumococcal vaccination to reduce the burden of pneumococcal disease in many countries worldwide [1]. Pneumococcal vaccination has been recommended in the UK in those with various clinical conditions since 1992, though uptake has been low [8]. Clinical risk groups have been defined as those with the following conditions: asplenia, chronic heart disease, chronic kidney disease, chronic liver disease, chronic respiratory disease, diabetes, immunosuppression, and individuals with cerebrospinal fluid leaks [9]. Cochlear implant patients were also considered, but the numbers were too small to report.

Currently, two pneumococcal vaccines are licensed and available for use in the UK in children over 5 years of age or adults at increased risk: the Pneumococcal Conjugate Vaccine (PCV13) which protects against 13 pneumococcal serotypes, and the Pneumococcal Polysaccharide Vaccine (PPV23) which protects against 23 pneumococcal serotypes [9]. In the UK, pneumococcal vaccination is typically administered in general practice.

The national pneumococcal immunisation programme for the UK was introduced in 2003 and initially offered PPV23 vaccination to all adults aged 80 years and older. By 2005, the programme had been extended to offer vaccination to all adults aged 65 years and over who were not previously immunised. In 2009, assessment of PPV23 vaccine uptake in patients aged 2–64 years within clinical risk groups was added to the annual survey of vaccine uptake [3, 10].

Current real-world data on pneumococcal vaccination coverage rates (VCR) in individuals aged 18–64 years with underlying medical conditions in the UK is limited. A 2012 Department of Health (DoH) report described data collected on at-risk patients vaccinated any time up and until 31st March 2009 [10]. It was reported that VCRs in at-risk individuals aged 16–64 years were only 34.4% during this time period in the UK. However, since 2009 the DoH have reported only the annual VCR in adults aged 65 years and older. Therefore, there is currently no recent UK report of the VCR for individuals with underlying medical conditions.

Our findings provide insight into pneumococcal vaccination patterns in individuals aged 18–64 years with underlying medical conditions in the UK. Despite the national recommendation for pneumococcal vaccination in clinical risk groups, only 13.6% of patients newly diagnosed with underlying medical conditions received a pneumococcal vaccination after 1 year of follow-up. After 4 years of follow-up, this rose to 32.0%. These low vaccination rates are disappointing, given the increased risk of pneumococcal disease in individuals with underlying medical conditions, and indicate that patients would benefit from measures to increase pneumococcal VCR within the UK. Consistent with previous research on factors associated with vaccine uptake, gender was significantly associated with pneumococcal vaccination in the univariate and multivariate analysis, respectively. There was also a non-significant trend that suggested age was associated with vaccine uptake. The improved rate of vaccination amongst those aged 50–64 may be due to increased physician contact, which has previously been associated with a significant increase in vaccination coverage [11]. A further factor may be that adults aged 50–64 are more likely to have comorbidities than those aged 18–49, and may have greater opportunity to be vaccinated. Similarly, it has been widely documented that rates of vaccination are greater for males than females [12], despite women having a higher prevalence of physician visits overall [13].

Substantial variation in vaccination rates was noted across regions of the UK and within England, with all regions except Wales having significantly better vaccination rates than the North East of England. This is perhaps due to the larger health inequalities experienced by patients in the North East. For example, a recent analysis found that primary care is underfunded in the North East, relative to the level of morbidity [14], which may result in lower vaccination rates. However, it should be noted that large differences in patient numbers were reported across regions of England, whilst variations in data collection and reporting procedures may also contribute to the disparity of results. Further investigation is required to identify the reasons for age-related, gender, and regional disparities in vaccination rates across the UK.

Current knowledge on pneumococcal vaccination coverage in individuals aged 18–64 years with underlying medical conditions is limited. A previously conducted DoH survey found that pneumococcal vaccine uptake reached 34.4% in individuals aged 16–64 years who were considered “at-risk” [10]. This correlates with the findings of this study, in which pneumococcal vaccine uptake reached 32.0% in individuals aged 18–64 years with underlying medical conditions. The slight difference in vaccination rates may be accounted for by the difference in study lengths, as this study was limited to a four-year period following diagnosis, whereas the DoH study accounted for patients receiving PPV vaccine any time until 2009. However, the results presented indicate that VCRs remain low within the population of interest, and further efforts should be made to increase the vaccination coverage within the UK.

After 1 year of follow-up, VCR in patients with one underlying medical condition were highest in those with diabetes mellitus (14.4%), and lowest in those with cerebrospinal fluid leaks (7.1%). After 4 years of follow-up, VCR rose in these patients to 31.8 and 21.2% respectively. Although there is an interval of nearly 10 years, these rates are comparable to those produced by the DoH where vaccination rates were lowest in those with cerebrospinal fluid leaks (16.3%) [10]. Given that age ranges and indications examined were similar between studies, the VCR discrepancy may in part be due to the low numbers of individuals diagnosed with cerebrospinal fluid leaks within the study period, which may result in inaccurate estimates of VCR rates within this population.

A 2019 study has also been conducted by Public Health England in at-risk patients aged 65 years and older, who were diagnosed and eligible for pneumococcal vaccination between April 2017 and March 2019. Within this report, individuals with cochlear implants had the highest rates of pneumococcal vaccination (52.2%), followed by diabetes mellitus (19.7%) and asplenia (17.8%). Individuals with cerebrospinal fluid leaks (6.5%) had the lowest rates of vaccination coverage [15]. The results presented by Public Health England mirror those found within this study, despite the different age ranges studied. However, it should also be noted that the number of patients diagnosed with each condition were not reported, and therefore direct comparisons cannot be applied.

Finally, individuals who received influenza vaccine in the first year of follow-up post index date were significantly more likely to receive pneumococcal vaccination than those who did not (P < 0.0001). Individuals with underlying medical conditions are recommended to receive influenza vaccination. The influenza season is annual, with focused national and local programmes to increase vaccine uptake – unlike pneumococcal vaccination. Therefore, the seasonal influenza programme offers an opportunity to provide pneumococcal vaccination alongside the influenza vaccine to unvaccinated individuals in risk groups. In 2014, NHS England introduced Enhanced Services specification to aid general practitioner (GP) practices in delivering seasonal influenza and pneumococcal vaccination programmes concurrently. As pneumococcal infection is a recognised complication of influenza, providing the two vaccines together early in the season will increase the level of protection to individuals with underlying conditions [16], and may result in improved long-term survival [5], while reducing appointment and administration costs.

Despite UK recommendations for pneumococcal vaccination in clinical risk groups, rates of pneumococcal vaccination may be suboptimal in UK individuals aged 18–64 with underlying medical conditions, with only 13.6% of the overall cohort receiving vaccination within 1 year of index date, rising to 32.0% after 4 years of follow-up. Further emphasis should be made on the importance of increased pneumococcal vaccination coverage in the UK, given the increased risk of morbidity and mortality within individuals with underlying medical conditions. Improved messaging on the importance of vaccination is key to improving vaccination rates. The results of this study reveal the low rate to decision makers, thereby helping to stimulate the development of strategies for addressing barriers to pneumococcal vaccination.