Initiation and duration of selective serotonin reuptake inhibitor prescribing over time: UK cohort study.

BACKGROUND: Recent media reports have focused on the large increase in antidepressants dispensed in England. We investigated this, focusing on selective serotonin reuptake inhibitors (SSRIs). AIMS: To examine the rate of initiation of SSRIs over time and changes over time in the duration of prescribing episodes. METHOD: We estimated initiation and duration of SSRI prescribing from 7 025 802 individuals aged over 18 years and registered with a general practice that contributed data to The Health Improvement Network. RESULTS: Rates of SSRI initiation increased from 1.03 per 100 person-years in 1995 to 2.15 in 2001, but remained stable from then to 2012. The median duration of prescribing episodes increased from 112 to 169 days for episodes starting in 1995 to 2010. CONCLUSIONS: Despite media reports describing an increasing rate of antidepressant prescribing, SSRI initiation rates have stabilised since 2001. However, our results suggest that individuals who take SSRIs are receiving treatment for longer.

Backdating of events in electronic primary health care data: should one censor at the date of last data collection.

PURPOSE: Studies using primary care databases often censor follow-up at the date data are last collected from clinical computer systems (last collection date (LCD)). We explored whether this results in the selective exclusion of events entered in the electronic health records after their date of occurrence, that is, backdated events. METHODS: We used data from The Health Improvement Network (THIN). Using two versions of the database, we identified events that were entered into a later (THIN14) but not an earlier version of the database (THIN13) and investigated how the number of entries changed as a function of time since LCD. Times between events and the dates they were recorded were plotted as a function of time since the LCD in an effort to determine appropriate points at which to censor follow-up. RESULTS: There were 356 million eligible events in THIN14 and 355 million eligible events in THIN13. When comparing the two data sets, the proportion of missing events in THIN13 was highest in the month prior to the LCD (9.6%), decreasing to 5.2% at 6 months and 3.4% at 12 months. The proportion of missing events was largest for events typically diagnosed in secondary care such as neoplasms (28% in the month prior to LCD) and negligible for events typically diagnosed in primary care such as respiratory events (2% in the month prior to LCD). CONCLUSIONS: Studies using primary care databases, particularly those investigating events typically diagnosed outside primary care, should censor follow-up prior to the LCD to avoid underestimation of event rates.

Estimating the diagnostic accuracy of rheumatoid factor in UK primary care: a study using the Clinical Practice Research Datalink.

OBJECTIVE: To investigate the diagnostic accuracy of RF as a test for RA in primary care and its impact on referral times using the Clinical Practice Research Datalink. METHODS: We identified all patients with a first RF test recorded in the Clinical Practice Research Datalink between 1 January 2000 and 31 December 2008 and those diagnosed with RA within 2 years of testing. We calculated likelihood ratios (LRs), sensitivity, specificity and predictive values of RF for a diagnosis of RA. We compared time to hospital referral in those testing positive and negative using Kaplan-Meier failure curves and log-rank tests. RESULTS: Of 62 436 first RF tests, 4679 (7.5%) were positive. There were 1753 incident cases of RA, of which 57.8% were seropositive. The positive LR for RF was 9.5 (95% CI 9.0, 10.0) and the negative LR was 0.5 (95% CI 0.4, 0.5). Sensitivity and specificity were 57.8% (95% CI 55.4%, 60.1%) and 93.9% (95% CI 93.7%, 94.1%) and the positive predictive value and negative predictive value were 21.4% (95% CI 20.3%, 22.6%) and 98.7% (95% CI 98.6%, 98.8%), respectively. Median time to first hospital contact after the first RF test in those with seropositive vs seronegative results was 54 days (95% CI 49, 58) vs 150 (95% CI 147, 152). CONCLUSION: Only 2.8% of patients undergoing RF testing were diagnosed with RA, suggesting that RF is used to screen patients with musculoskeletal symptoms rather than those with more specific features of RA. A positive RF test may be helpful in diagnosing RA in primary care but performs badly in excluding RA and may delay referral.

Missing laboratory test data in electronic general practice records: analysis of rheumatoid factor recording in the clinical practice research datalink.

PURPOSE: To investigate whether information from the literature could be used to identify periods of practice data in an electronic healthcare database during which rheumatoid factor (RF) test results are likely to be missing-not-at-random (MNAR). METHODS: RF tests recorded in the Clinical Practice Research Datalink (CPRD) were identified and defined as having a positive, negative or missing result. The proportion of positive test results was then calculated based on (i) complete-case analysis (ii) after restriction to tests from practice years with no missing test results and (iii) following multiple imputation of missing test results. The same three analyses were then carried out after excluding practice years with a proportion of positive tests incompatible with the missing completely at random (MCAR) assumption. RESULTS: We identified 127,969 RF test records, 30.4% of which did not have an associated test result. Among tests with results available, 19% were positive. Both multiple imputation of the 38,867 missing test results and restriction of the study population to the 491 practice years with complete data had little impact on the percentage of positive tests. Following exclusion of the 544 practice years in which data were likely to be MNAR the percentage of positive tests in all analyses decreased to ~7%. CONCLUSIONS: Recording of RF tests and RF test results in the CPRD is incomplete, with data likely to be MNAR in many practices. Exclusion of practice years with a high proportion of positive tests brought the distribution of positive tests in the study in line with the literature.

Nonindependence of patient data in the clinical practice research datalink: a case study in atrial fibrillation patients.

Aim: The impact of different strategies to handle patients with data recorded under multiple Clinical Practice Research Datalink (CPRD) identifiers (IDs) is unknown. Patients and methods: Six approaches to handling patients appearing under multiple CPRD IDs were defined. The impact of the approaches was illustrated using a case study describing the clinical characteristics of a population of nonvalvular atrial fibrillation patients. Results: 5.6% of patients had more than one CPRD ID. Across all six approaches implemented, no material difference in the characteristics of nonvalvular atrial fibrillation patients were observed. Conclusion: While strategies which longitudinally append patient registration periods under different CPRD IDs maintain independence while using all available data, their implementation had little impact on the results of our case study.

Impact of atrial fibrillation awareness campaigns: interrupted time series using the Clinical Practice Research Datalink.

Aim: This study investigated whether the rates of atrial fibrillation (AF) consultations changed following AF awareness campaigns in England. Materials & methods: Among adults in the Clinical Practice Research Datalink, Poisson regression was used to model weekly rates of AF-related consultations over time. The models were used to assess whether rates changed in the 8 weeks following World Heart Rhythm Week (WHRW) and Global AF aware week. Results: A higher incidence of pulse checks was observed following WHRW (IRR 1.16 [95% CI 1.08-1.24]). No difference in the incidence of AF diagnoses was noted following WHRW (IRR: 1.03 [95% CI: 0.97-1.09]) or Global AF aware week (IRR: 0.94 [95% CI: 0.88-1.00]). Conclusion: The results suggest AF campaigns may increase awareness but do not bring about short-term increases in the rates of AF diagnoses.

Costs of gastrointestinal bleeding events in atrial fibrillation: a UK Clinical Practice Research Datalink study.

Aim: To estimate the healthcare costs attributable to gastrointestinal (GI) bleeds in nonvalvular atrial fibrillation (NVAF) patients. Material & methods: A difference-in-differences approach was used in which NVAF patients suffering a (GI) bleed were propensity score matched to those not suffering a GI bleed, and the difference in healthcare costs in the year prior to the GI bleed and the subsequent 3 years was compared between the two groups. Results: The mean cost attributable to GI bleeds was £3989 (p < 0.0001) in the year of the bleed and £1816 (p = 0.001) in the subsequent year. Attributable costs arose primarily from inpatient visits. Conclusion: GI bleeds among NVAF patients are associated with significant healthcare costs up to 2 years following the bleed.

Renal function and oral anticoagulant treatment of incident non-valvular atrial fibrillation: a retrospective study.

Aim: To describe the renal function of individuals newly diagnosed with non-valvular atrial fibrillation in England, and describe how oral anticoagulant (OAC) treatment varies according to renal function. Patients & methods: We identified a cohort of individuals with non-valvular atrial fibrillation (n = 18,419) and described their renal function at diagnosis and the prevalence of OAC treatment initiation by renal function. Results: 79% of individuals had some evidence of renal dysfunction with 12% having a glomerular filtration rate <30 ml/min/1.73 m2. OAC treatment initiation in the 6 months following diagnosis was lower in individuals with severe renal dysfunction than in those with normal renal function. Conclusion: The high prevalence of renal dysfunction and low OAC treatment prevalence highlights the need for additional evidence regarding OACs in individuals with severe renal dysfunction.

Under-recording of hospital bleeding events in UK primary care: a linked Clinical Practice Research Datalink and Hospital Episode Statistics study.

BACKGROUND: Primary care databases represent a rich source of data for health care research; however, the quality of recording of secondary care events in these databases is uncertain. This study sought to investigate the completeness of recording of hospital admissions for bleeds in primary care records and explore the impact of incomplete recording on estimates of bleeding risk associated with antithrombotic treatment. METHODS: The study population consisted of adults with non-valvular atrial fibrillation who had at least one bleed recorded in either the Clinical Practice Research Datalink (CPRD) or Hospital Episode Statistics (HES) while receiving prescriptions for an oral anticoagulant. The proportion of bleeds recorded in HES that had a corresponding bleed recorded in the subsequent 12 weeks in CPRD was calculated, and factors associated with having a corresponding record were identified. Cox proportional hazards analyses investigating the hazard of subsequent bleeding associated with antithrombotic treatment were carried out using linked CPRD-HES data and using CPRD only data, and the results were compared. RESULTS: Less than 20% of the 14,361 bleeds recorded in the HES data had a corresponding bleed coded in the CPRD in the subsequent 12 weeks. This proportion varied by bleed characteristics, calendar time, day of week of admission (weekday vs weekend) and oral anticoagulant treatment at the time of the bleed. The hazard of subsequent bleeding associated with vitamin K antagonists (VKAs) and antiplatelet agents (APAs) relative to no antithrombotic treatment were similar using the linked primary and secondary care dataset (VKA HRadj 1.06 CI95 0.96-1.16; APA HRadj 1.08 CI95 0.96-1.21) and the unlinked primary care data (VKA HRadj 1.12 CI95 1.01-1.24; APA HRadj 1.06 CI95 0.95-1.20). CONCLUSION: Secondary care bleeding events are not completely recorded in primary care records and under-recording may be differential with respect to a variety of factors, including antithrombotic treatment. While the impact of under-recording on estimates of the comparative safety of antithrombotic drugs was limited, the extent of the under-recording suggests its potential impact should be considered, and ideally evaluated in future studies utilizing standalone primary care data.

Antiepileptic drugs prescribed in pregnancy and prevalence of major congenital malformations: comparative prevalence studies.

OBJECTIVE: The aim of this study was to examine the prevalence of major congenital malformations associated with antiepileptic drug (AED) treatment in pregnancy. PATIENTS AND METHODS: Using data from The Health Improvement Network, we identified women who have given live birth and their offspring. Four subgroups were selected based on the AED treatment in early pregnancy, valproate, carbamazepine, lamotrigine and women not receiving AED treatment. We compared the prevalence of major congenital malformations within children of these four groups and estimated prevalence ratios (PRs) using Poisson regression adjusted for maternal age, sex of child, quintiles of Townsend deprivation score and indication for treatment. RESULTS: In total, 240,071 women were included in the study. A total of 229 women were prescribed valproate in pregnancy, 357 were prescribed lamotrigine and 334 were prescribed carbamazepine and 239,151 women were not prescribed AEDs. Fifteen out of 229 (6.6%) women prescribed valproate gave birth to a child with a major congenital malformation. The figures for lamotrigine, carbamazepine and women not prescribed AEDs were 2.7%, 3.3% and 2.2%, respectively. The prevalence of major congenital malformation was similar for women prescribed lamotrigine or carbamazepine compared to women with no AED treatment in pregnancy. For women prescribed valproate in polytherapy, the prevalence was fourfold higher. After adjustments, the effect of estimates attenuated, but the prevalence remained two- to threefold higher in women prescribed valproate. CONCLUSION: The results of our study suggest that lamotrigine and carbamazepine are safer treatment options than valproate in pregnancy and should be considered as alternative treatment options for women of childbearing potential and in pregnancy.

Recording and treatment of premenstrual syndrome in UK general practice: a retrospective cohort study.

OBJECTIVES: To investigate the rate of recording of premenstrual syndrome diagnoses in UK primary care and describe pharmacological treatments initiated following a premenstrual syndrome (PMS) diagnosis. DESIGN: Retrospective cohort study. SETTING: UK primary care. PARTICIPANTS: Women registered with a practice contributing to The Health Improvement Network primary care database between 1995 and 2013. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was the rate of first premenstrual syndrome records per 1000 person years, stratified by calendar year and age. The secondary outcome was the proportions of women with a premenstrual syndrome record prescribed a selective serotonin reuptake inhibitor, progestogen, oestrogen, combined oral contraceptive, progestin only contraceptive, gonadotrophin-releasing hormone, danazol and vitamin B6. RESULTS: The rate of recording of premenstrual syndrome diagnoses decreased over calendar time from 8.43 in 1995 to 1.72 in 2013. Of the 38,614 women without treatment in the 6 months prior to diagnosis, 54% received a potentially premenstrual syndrome-related prescription on the day of their first PMS record while 77% received a prescription in the 24 months after. Between 1995 and 1999, the majority of women were prescribed progestogens (23%) or vitamin B6 (20%) on the day of their first PMS record; after 1999, these figures fell to 3% for progestogen and vitamin B6 with the majority of women instead being prescribed a selective serotonin reuptake inhibitor (28%) or combined oral contraceptive (17%). CONCLUSIONS: Recording of premenstrual syndrome diagnoses in UK primary care has declined substantially over time and preferred prescription treatment has changed from progestogen to selective serotonin reuptake inhibitor and combined oral contraceptives.

Risks associated with antipsychotic treatment in pregnancy: Comparative cohort studies based on electronic health records.

BACKGROUND: Limited information is available on whether antipsychotics prescribed in pregnancy are associated with increased risks of adverse outcomes. METHODS: We used electronic health records from pregnant women and their children to examine risks of adverse maternal and child outcomes in three cohorts of women who: (A) received antipsychotic treatment in pregnancy (n=416) (B) discontinued antipsychotic treatment before pregnancy (n=670), and (C) had no records of antipsychotic treatment before or during pregnancy (n=318,434). Absolute and risk ratios were estimated and adjusted for health and lifestyle and concomitant medications. RESULTS: Caesarean section was more common in cohort A (25%) than C (18%), but non-significant after adjustment for health and lifestyle factors (Risk Ratio (adj.) 1.09 (95% CI: 0.92, 1.30). Proportion of gestational diabetes was similar in cohort A (2.6%) and B (2.7%), but lower in A than B after adjustments (RRadj: 0.43 (0.20, 0.93). Premature birth/low birthweight were more common in cohort A (10%) than B (4.3%) and C (3.9%), A versus B (RRadj: 2.04 (1.13, 3.67), A versus C (RRadj: 1.43 (0.99, 2.05). Major congenital malformations were more common in A (3.4%), than B (2.2%) and C (2%). However no significant difference was observed (A versus B: RRadj: 1.79 (0.72, 4.47) A versus C RRadj: 1.59 (0.84, 3.00)). Risks estimates were similar for women prescribed atypical and typical antipsychotics. CONCLUSIONS: Antipsychotic treatment in pregnancy carries limited risks of adverse pregnancy and birth outcomes once adjustments have been made for health and lifestyle factors.

Risks and benefits of psychotropic medication in pregnancy: cohort studies based on UK electronic primary care health records.

BACKGROUND: Although many women treated with psychotropic medication become pregnant, no psychotropic medication has been licensed for use in pregnancy. This leaves women and their health-care professionals in a treatment dilemma, as they need to balance the health of the woman with that of the unborn child. The aim of this project was to investigate the risks and benefits of psychotropic medication in women treated for psychosis who become pregnant. OBJECTIVE(S): (1) To provide a descriptive account of psychotropic medication prescribed before pregnancy, during pregnancy and up to 15 months after delivery in UK primary care from 1995 to 2012; (2) to identify risk factors predictive of discontinuation and restarting of lithium (multiple manufacturers), anticonvulsant mood stabilisers and antipsychotic medication; (3) to examine the extent to which pregnancy is a determinant for discontinuation of psychotropic medication; (4) to examine prevalence of records suggestive of adverse mental health, deterioration or relapse 18 months before and during pregnancy, and up to 15 months after delivery; and (5) to estimate absolute and relative risks of adverse maternal and child outcomes of psychotropic treatment in pregnancy. DESIGN: Retrospective cohort studies. SETTING: Primary care. PARTICIPANTS: Women treated for psychosis who became pregnant, and their children. INTERVENTIONS: Treatment with antipsychotics, lithium or anticonvulsant mood stabilisers. MAIN OUTCOME MEASURES: Discontinuation and restarting of treatment; worsening of mental health; acute pre-eclampsia/gestational hypertension; gestational diabetes; caesarean section; perinatal death; major congenital malformations; poor birth outcome (low birthweight, preterm birth, small for gestational age, low Apgar score); transient poor birth outcomes (tremor, agitation, breathing and muscle tone problems); and neurodevelopmental and behavioural disorders. DATA SOURCES: Clinical Practice Research Datalink database and The Health Improvement Network primary care database. RESULTS: Prescribing of psychotropic medication was relatively constant before pregnancy, decreased sharply in early pregnancy and peaked after delivery. Antipsychotic and anticonvulsant treatment increased over the study period. The recording of markers of worsening mental health peaked after delivery. Pregnancy was a strong determinant for discontinuation of psychotropic medication. However, between 40% and 76% of women who discontinued psychotropic medication before or in early pregnancy restarted treatment by 15 months after delivery. The risk of major congenital malformations, and neurodevelopmental and behavioural outcomes in valproate (multiple manufacturers) users was twice that in users of other anticonvulsants. The risks of adverse maternal and child outcomes in women who continued antipsychotic use in pregnancy were not greater than in those who discontinued treatment before pregnancy. LIMITATIONS: A few women would have received parts of their care outside primary care, which may not be captured in this analysis. Likewise, the analyses were based on prescribing data, which may differ from usage. CONCLUSIONS: Psychotropic medication is prescribed before, during and after pregnancy. Many women discontinue treatment before or during early pregnancy and then restart again in late pregnancy or after delivery. Our results support previous associations between valproate and adverse child outcomes but we found no evidence of such an association for antipsychotics. FUTURE WORK: Future research should focus on (1) curtailing the use of sodium valproate; (2) estimating the benefits of psychotropic drug use in pregnancy; and (3) investigating the risks associated with lifestyle choices that are more prevalent among women using psychotropic drugs. FUNDING DETAILS: The National Institute for Health Research Health Technology Assessment programme.

The incidence of childhood and adolescent seizures in the UK from 1999 to 2011: A retrospective cohort study using the Clinical Practice Research Datalink.

BACKGROUND: In postmarketing vaccine surveillance, adverse events observed in a vaccinated population are compared to the number expected based on a background incidence rate. The background rate should be accurate and obtained from a population comparable to the one vaccinated. Such rates are often not available. METHODS: The incidence rate of generalised convulsive, febrile and afebrile seizures was estimated in individuals born after 01-January-1998 and aged between 2 months and 15 years of age using the UK Clinical Practice Research Datalink (1999-2011). RESULTS: The study population consisted of 1532,992 individuals (4917,369 person years (PY) of follow up). A total of 28,917 generalised convulsive seizure events were identified during follow-up, the overall incidence rate was 5.88 per 1000PY. Age specific rates increased sharply from 4/1000PY at 2 months of age, peaked at 19/1000PY at 16 months and decreased until approximately 6 years of age at which point they became relatively stable at 2/1000PY. 67% of GCSs were categorised as febrile: 56% using Read codes, 11% using free text. Febrile seizures accounted for the age trend in GCS, with rates peaking at 16.1/1000PY at 16 months of age while afebrile seizure rates remained relatively stable across all ages (24 seizures per 1000PY). Analysis by first occurrence of febrile seizure showed a similar pattern, comparable to published studies on the incidence of seizures in childhood. DISCUSSION: The rates reported in this study could be used in the postmarketing surveillance of infant vaccines. However, given the variation across strata, and the potential underascertainment of seizure events presenting to A&E, care must be taken when interpreting and using these rates.

Pandemic influenza vaccination during pregnancy: an investigation of vaccine uptake during the 2009/10 pandemic vaccination campaign in Great Britain.

BACKGROUND: Pregnant women in Great Britain were recommended to receive influenza A(H1N1)pdm09 vaccines during the 2009/10 influenza pandemic, however uptake of the vaccines by pregnant women was reported to have been very low. AIM: We sought to estimate uptake of influenza A(H1N1)pdm09 vaccines and to investigate predictors of vaccine uptake in pregnant women in Great Britain during the 2009/10 pandemic. RESULTS: Uptake of influenza A(H1N1)pdm09 vaccines by pregnant women was 21.6%. Pregnant women with an underlying health condition increasing the risk of influenza-related complications had a higher vaccination rate than pregnant women without such conditions. The hazard ratio comparing these two groups decreased logarithmically throughout pregnancy from 9.3 in the first week to 1.3 by the end of pregnancy. Increasing maternal age (HR 1.01, CI 95 1.01-1.01), having a previous delivery recorded (HR 1.21, CI95 1.16-1.27) and living in Scotland (HR 2.58, CI95 2.34-2.85) or Wales (HR 1.37, CI95 1.20-1.57) as opposed to England were all also associated with an increase in vaccination uptake rates throughout pregnancy. DISCUSSION: Uptake of influenza A(H1N1)pdm09 vaccines by pregnant women was low. None of the potential predictors evaluated in this study were strong enough to account for this, however information on health beliefs and GP recommendation were not available. If the low rates reported here are to be improved new strategies to increase uptake of influenza vaccine in pregnant women need to be identified, evaluated and implemented. METHODS: Uptake rates were calculated using data from the UK General Practice Research Database (GPRD). Predictors of vaccination were identified using a Cox proportional hazards model.

Evaluating the hazard of foetal death following H1N1 influenza vaccination; a population based cohort study in the UK GPRD.

BACKGROUND: To evaluate the risk of foetal loss associated with pandemic influenza vaccination in pregnancy. Retrospective cohort study. UK General Practice Research Database Pregnancies ending in delivery or spontaneous foetal death after 21 October 2009 and starting before 01 January 2010. METHODOLOGY/PRINCIPAL FINDINGS: Hazard ratios of foetal death for vaccinated compared to unvaccinated pregnancies were estimated for gestational weeks 9 to 12, 13 to 24 and 25 to 43 using discrete-time survival analysis. Separate models were specified to evaluate whether the potential effect of vaccination on foetal loss might be transient (for ~4 weeks post vaccination only) or more permanent (for the duration of the pregnancy). 39,863 pregnancies meeting our inclusion criteria contributed a total of 969,322 gestational weeks during the study period. 9,445 of the women were vaccinated before or during pregnancy. When the potential effect of vaccination was assumed to be transient, the hazard of foetal death during gestational weeks 9 through 12 (HR(unadj) 0.56; CI(95) 0.43 to 0.73) and 13 through 24 (HR(unadj) 0.45; CI(95) 0.28 to 0.73) was lower in the 4 weeks after vaccination than in other weeks. Where the more permanent exposure definition was specified, vaccinated pregnancies also had a lower hazard of foetal loss than unvaccinated pregnancies in gestational weeks 9 through 12 (HR(unadj) 0.74; CI(95) 0.62 to 0.88) and 13 through 24 (HR(unadj) 0.59; CI(95) 0.45 to 0.77). There was no difference in the hazard of foetal loss during weeks 25 to 43 in either model. Sensitivity analyses suggest the strong protective associations observed may be due in part to unmeasured confounding. CONCLUSIONS/SIGNIFICANCE: Influenza vaccination during pregnancy does not appear to increase the risk of foetal death. This study therefore supports the continued recommendation of influenza vaccination of pregnant women.

Factors associated with uptake of seasonal and pandemic influenza vaccine among clinical risk groups in the UK: an analysis using the General Practice Research Database.

BACKGROUND: Influenza vaccine uptake rates are low compared with uptake rates of many other vaccines. It is unclear how this differs between risk groups in the population and between pandemic and non-pandemic influenza vaccines. AIM: This study sought to estimate uptake rates of pandemic and seasonal influenza vaccines among clinical risk groups in the UK during the 2009/2010 influenza season and to identify predictors of vaccine uptake in this cohort. METHODS: Uptake rates were calculated using data from the UK General Practice Research Database (GPRD). Predictors of vaccination were identified using a modified Poisson regression with robust standard error estimates. RESULTS: Uptake of pandemic influenza vaccine in clinical risk groups was 40.3% and uptake of seasonal influenza vaccine was 61.3%. Factors found to be predictive of seasonal and pandemic influenza vaccination included age and the total number of underlying health conditions an individual had. At risk individuals in those age groups in which universal vaccination of the general population was recommended were more likely to have been vaccinated than individuals in age groups in which only clinical risk groups were recommended for vaccination; hence children in clinical risk groups were more likely to receive pandemic than seasonal influenza vaccine. In older people, having a history of Guillain Barré syndrome was associated with a reduced likelihood of receipt of both seasonal (IRR(adj) 0.83, CI(95) 0.77-0.90) and pandemic influenza vaccines (IRR(adj) 0.82, CI(95) 0.73-0.92). DISCUSSION: Uptake of pandemic influenza vaccine was lower than that of seasonal influenza vaccine among those at a clinically high risk of influenza related morbidity. This suggests that vaccination strategies may need to be altered during future pandemics. Recommending universal vaccination within age categories in which there is a large proportion of high risk individuals could be considered as this may result in higher uptake among clinical risk groups.