Vaccine 32 (2014) 2204–2208

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General practice encounters following seasonal influenza vaccination as a proxy measure of early-onset adverse events A. Dey a,b,∗ , H.F. Gidding a,c , R. Menzies a,b , P. McIntyre a,b,d,e a

National Centre for Immunisation Research and Surveillance, Sydney, NSW, Australia Discipline of Paediatrics and Child Health, University of Sydney, Sydney, NSW, Australia School of Public Health and Community Medicine, University of New South Wales, Sydney, NSW, Australia d School of Public Health, University of Sydney, Sydney, NSW, Australia e The Children’s Hospital at Westmead, Sydney, NSW, Australia b c

a r t i c l e

i n f o

Article history: Received 23 September 2013 Received in revised form 7 February 2014 Accepted 12 February 2014 Available online 6 March 2014 Keywords: Primary care General practice Influenza Adverse events

a b s t r a c t Background: In 2010, use of seasonal trivalent influenza vaccine (TIV) in children 2 years) and region (Western Australia vs other Australian states/territories). Conclusions: A primary care consultation on the day after vaccine receipt is a reasonable proxy for early reactogenicity and has potential for use in various settings. © 2014 Elsevier Ltd. All rights reserved.

1. Introduction In Australia, there has been a number of changes in the use and availability of influenza vaccines in children under five years of age in the last decade. In the Australian Immunisation Handbook, 8th edition, 2003 [1] influenza vaccine was recommended for all children in this age group, due to high rates of hospitalization [1–3]. However, it was not funded at a national or regional level prior to 2008. In 2008, the state of Western Australia (WA) initiated a free program of influenza vaccine for all children under five years following a number of influenza-related deaths identified in WA children in 2007 [4]. In July 2009, it was announced that

∗ Corresponding author at: National Centre for Immunisation Research and Surveillance, Westmead, NSW, Australia. Tel.: +61 2 9845 1416; fax: +61 2 9845 1418. E-mail addresses: [email protected], aditi [email protected] (A. Dey). http://dx.doi.org/10.1016/j.vaccine.2014.02.044 0264-410X/© 2014 Elsevier Ltd. All rights reserved.

seasonal influenza vaccine would be available free of charge under the National Immunisation Program (NIP) from 2010 onwards for all persons over the age of six months who had one or more conditions predisposing them to severe influenza [5]. From December 2009, pandemic H1N1 vaccine, Panvax® (monovalent influenza vaccine of bioCSL, formerly CSL Biotherapies) was made available free of charge to all Australian children six months and older [6,7], having been available for individuals over the age of 10 years since the end of September 2009 [8]. Influenza vaccination campaigns commenced in early March 2010. On 29 April 2010, the use of seasonal influenza vaccines in children aged less than five years of age was suspended nationally, following reports of severe febrile illness and febrile convulsions occurring within 24–48 h of administration of seasonal influenza vaccine in Western Australian children, especially those less than two years of age [9–12]. Following further investigations, the seasonal trivalent influenza vaccine produced by only one manufacturer (bioCSL) was implicated [13]. Data were more limited from

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regions other than WA or for other influenza vaccines, including CSL Monovalent influenza vaccine. In particular, it was unclear to what extent stimulated reporting had enhanced the observed signal for 2010 CSL seasonal trivalent influenza vaccine (TIV) in children. All vaccines administered to children aged less than seven years should be reported to the Australian Childhood Immunisation Register (ACIR) [14]. The ACIR constitutes a nearly complete population register, as approximately 99% of children are registered with Medicare Australia by 12 months of age [15]. Influenza vaccines are also reported to ACIR though not routinely and are likely to be less completely recorded compared to vaccines included on the NIP such as those for pertussis or measles, mumps and rubella. Australia’s universal health system provides GP and other services to all permanent residents. Each consultation is claimed and reported, linked to the respective patients’ unique identifier (Medicare number). However, the reason of consultation is not reported. As GP consultations and ACIR data are both held by Medicare Australia, Australian Government Department of Human Services [14], these datasets can be linked with by the Medicare number. We aimed to determine how well early re-presentation to general practice for any reason, following receipt of a vaccine, performed as a proxy measure of early-onset vaccine adverse events. We used the 2010 CSL manufactured TIV as a reference standard, to compare the results obtained from this method with those from other studies. Specifically, we aimed to compare rates of re-presentation following 2010 CSL TIV with those of other influenza vaccines, including those made by CSL in previous years, and those made by another manufacturer. Our methods are similar to those used in a published study of whole cell vs acellular pertussis vaccine early reactogenicity from the United Kingdom, the only other study where GP consultation data have been used to compare reactogenicity in infants of two different vaccine types [16].

incidence rate ratios were estimated by controlling for age group and region. Incidence rate ratios were estimated for (1) CSL TIV, 2010 vs CSL TIV, 2008–2009; (2) CSL Monovalent, 2009–2010 vs CSL TIV, 2010; (3) Sanofi Pasteur TIV, 2009–2010 vs CSL TIV, 2010; (4) CSL TIV, 2008–2009 vs Sanofi Pasteur TIV, 2009–2010; (5) CSL TIV, 2008–2009 vs CSL Monovalent, 2009–2010; and (6) CSL Monovalent, 2009–2010 vs Sanofi Pasteur TIV, 2009–2010. Years were combined for some comparisons, where appropriate, due to small sample sizes. Analyses were performed using STATA version 12 and Microsoft Excel 2010.

2. Methods

4.1. CSL TIV, 2010 vs CSL TIV, 2008–2009

GP encounters following ACIR-recorded receipt of an influenza vaccine were obtained for children aged seven months to 60 months from Medicare Australia. There was further breakdown of the GP encounter data by region, recorded influenza vaccine type, age group at vaccination, month and year of vaccination. The data were provided as aggregated data in tabular form and extracted by Medicare Australia initially in May 2010. This initial dataset was used for preliminary analysis to inform the Australian Technical Advisory Group on Immunisation (ATAGI) that provides advice to the Minister for Health on the Immunise Australia Program and other related issues. A final complete dataset, including the whole of 2010 calendar year, was requested from Medicare Australia in 2011. This data was extracted by Medicare Australia in September 2011. We used this final dataset for analysis in this study. For the analysis presented here, GP encounters were categorized as follows: “Day 0” the day of vaccination; “Day 1” the day following vaccination, Day 2–3 the 2nd and 3rd day following vaccination. Pre-Day1 was the corresponding day before vaccination. The following influenza vaccine types and years were investigated: CSL TIV 2008–2010; CSL Monovalent influenza vaccine, 2009–2010 and Sanofi Pasteur TIV, 2009–2010.

In both WA and regions other than WA, the GP encounter rate per 1000 doses on Day 1 following CSL TIV vaccination in 2010 was higher than in 2008–2009 (Table 1). This was the case for each age group and all ages combined. Even though the GP encounter rate on Day 1 following CSL TIV vaccination in WA was lower than in the other regions, the rate ratio (2010 vs 2008–2009) for all ages combined for WA (RR 1.8; 95% CI 1.5–2.2) was almost identical to that for other regions (RR 1.9; 95% CI 1.6–2.4). Hence overall, and for each age group separately, the incidence rate ratios (CSL TIV 2010 vs 2008–2009) were significantly increased, with ages seven–24 months experiencing the greatest increase (Table 2).

2.1. Data analysis

4.3. CSL TIV, 2010 vs Sanofi Pasteur TIV, 2009–2010

Rates of GP encounters per day per 1000 vaccine doses, with 95% confidence intervals were calculated for children aged seven months to 60 months by age group (≤2, >2 years), year, and region (Western Australia vs other states/territories). Unadjusted and adjusted incidence rate ratios with 95% confidence intervals were also determined using Poisson regression models. Adjusted

The GP encounter rate per 1000 doses on Day 1 following CSL TIV 2010 vaccination was significantly higher than that found for Sanofi Pasteur TIV in 2009–2010 in both WA and in the other regions for children aged between seven months to ≤60 months, (Table 1) and this was also reflected in significantly higher incidence rate ratios for CSL TIV 2010 vs Sanofi Pasteur TIV 2009–2010 (Table 2).

3. Ethical review The National Centre for Immunisation Research and Surveillance (NCIRS), as part of its responsibilities under a funding agreement with the Australian Government Department of Health (DoH), takes a lead role in evaluating national immunization programs. As we conducted our study using de-identified, aggregated data in tabular form supplied by Medicare Australia for the purposes of national program evaluation, specific ethics approval was not required. 4. Results When examining GP encounters by pre- and post-vaccination periods, there were significant differences between CSL TIV, 2010 and the other vaccines only with respect to Day 1 encounters (Fig. 1). Therefore, we conducted the comparative analyses using Day 1 GP encounters.

4.2. CSL TIV, 2010 vs CSL Monovalent, 2009–2010 In both WA and regions other than WA, the GP encounter rate per 1000 doses on Day 1 following CSL TIV in 2010 was higher than for CSL Monovalent influenza vaccine during 2009–2010 (Table 1). Hence, the incidence rate ratios (CSL TIV in 2010 vs CSL Monovalent 2009–2010) by age group and overall were significantly raised (Table 2).

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Fig. 1. GP encounters following influenza immunization in children aged 7 months to ≤60 months, Australia, 2008–2010.

Table 1 GP encounters on Day 1 following influenza vaccination by age, regions and vaccine types, Australia, 2008–2010. Regions

CSL TIV 2010 Vaccine (number)

a

CSL TIV 2008–2009 Ratea

95% CI

Vaccine (number)

Ratea

Western Australia (WA) 4218 7–24 mo 5984 25 mo-60 mo 10,202 7 mo-60 mo

17.3 9.2 12.5

13.6–21.8 6.9–12.0 10.5–14.9

22,387 28,358 50,745

7.1 6.8 6.9

Other States & Territories 2486 7–24 mo 6316 25 mo-60 mo 7 mo-60 mo 8802

21.7 16.5 18.0

16.3–28.3 13.5–20.0 15.3–21.0

8808 19,022 27,830

10.3 8.8 9.3

CSL Monovalent 2009–2010 95% CI

6.1–8.3 5.8–7.8 6.2–7.7 8.3–12.7 7.5–10.2 8.2–10.5

Vaccine (number)

Ratea

95% CI

Sanofi Pasteur TIV 2009–2010 Vaccine (number)

Ratea

1855 2701 4556

6.5 4.8 5.5

3.3–11.3 2.6–8.2 3.6–8.1

10,669 13,532 24,201

6.2 5.1 5.6

31,647 57,997 89,644

9.4 7.3 8.0

8.3–10.5 6.6–8.0 7.4–8.6

1902 4131 6033

11.0 8.0 9.0

95% CI

4.8–7.9 4.0–6.5 4.7–6.6 6.8–16.9 5.5–11.2 6.7–11.7

Per day per 1000 vaccine doses.

Table 2 Incidence Rate Ratios (IRR) of GP encounters by vaccine type and age groups on Day 1 following influenza vaccination, Australia, 2008–2010. Comparison

Crude (95% CI)

Adjusteda (95% CI)

7–24 mo 25 mo-60 mo All ages (7–60 mo)

2.35 (1.90–2.91) 1.71 (1.42–2.06) 1.93 (1.68–2.23)

1.88 (1.64–2.17)

CSL TIV 2010 vs CSL Monovalent 2009–2010

7–24 mo 25 mo-60 mo All ages (7–60 mo)

2.06 (1.68–2.53) 1.80 (1.50–2.16) 1.91 (1.66–2.18)

2.29 (1.95–2.69)

CSL TIV 2010 vs Sanofi Pasteur TIV 2009–2010

7–24 mo 25–60 mo All ages (7–60 mo)

1.65 (1.44–1.90) 1.50 (1.32–1.69) 1.55 (1.42–1.70)

1.48 (1.34–1.62)

CSL TIV 2008–2009 vs Sanofi Pasteur TIV 2009–2010

7–24 mo 25–60 mo All ages (7–60 mo)

1.08 (0.95–1.22) 1.15 (1.03–1.28) 1.11 (1.03–1.21)

1.08 (1.00–1.18)

CSL TIV 2008–2009 vs CSL Monovalent 2009–2010

7–24 mo 25–60 mo All ages (7–60 mo)

0.88 (0.74–1.03) 1.05 (0.92–1.21) 0.98 (0.88–1.09)

1.17 (1.03–1.34)

CSL Monovalent 2009–2010 vs Sanofi Pasteur TIV 2009–2010

7–24 mo 25–60 mo All ages (7–60 mo)

1.32 (1.05–1.69) 1.24 (1.00–1.54) 1.26 (1.08–1.48)

0.92 (0.72–1.16)

CSL TIV 2010 vs CSL TIV 2008–2009

a

IRR

Adjusted by age group, state & territory (WA, other regions combined).

A. Dey et al. / Vaccine 32 (2014) 2204–2208

4.4. CSL TIV, 2008–2009 vs Sanofi Pasteur TIV, 2009–2010 The Day 1 GP consultation rate per 1000 doses on Day 1 for CSL TIV in 2008–2009 was slightly higher than for Sanofi Pasteur TIV in 2009–2010 but after adjustment for age and region the difference was not statistically significant (Table 2). 4.5. CSL Monovalent, 2009–2010 vs CSL TIV, 2008–2009 and Sanofi Pasteur TIV, 2009–2010 The Day 1 GP consultation rate per 1000 doses on Day 1 for CSL TIV 2008–2009 was significantly higher than for CSL Monovalent, 2009–2010, although the rate increase was significantly lower than that for the comparison of CSL TIV 2010 with CSL Monovalent, 2009–2010 (Table 2). There was no significant difference in the rate of consultations for CSL Monovalent, 2009–2010 and Sanofi Pasteur TIV, 2009–2010 (Table 2). 5. Discussion Using the linked general practice encounters and ACIR data for receipt of an influenza vaccine, obtained from Medicare Australia, we found a significant increase in general practice encounters on the day following vaccination with CSL TIV in 2010 compared to previous CSL influenza vaccines and other influenza vaccines. This was a timely and sensitive method for detecting an increase in adverse events following immunization using a national linked dataset. This increase was observed in WA and in other regions despite rates being lower in WA, and remained when adjusted for potential confounders. Our findings are consistent with those from other Australian studies on adverse events following immunization with CSL TIV in 2010 [9,11,17–21] and lends some confidence to the ancillary findings of a lack of such a signal with a seasonal influenza vaccine from other manufacturers or CSL TIV in previous years. Specifically, our study findings are similar to a study that found a significantly higher parental report of visiting a general practitioner within 48 h after administration of the CSL TIV in 2010 compared with the CSL Monovalent influenza vaccine (RR, 3.0; 95% CI, 1.3–6.8; P < 0.01) and TIV from another manufacturer (RR, 8.2; 95% CI, 1.9–35.4; P = 0.001) [21]. General practice encounters to assess reactogenicity of vaccines have been used in overseas studies as well [16,22,23]. Particularly, in the United Kingdom, general practitioner consultation data were used to compare the reactogenicity in infants of an acellular pertussis vaccine to the whole cell-pertussis vaccine and found that the relative incidence of specified adverse events following immunization was significantly above one on the day of vaccination [16]. That study used the General Practice Research Database (GPRD), a primary care database that holds data on consultations, referrals, prescriptions and vaccinations for over 3 million active patients in practices throughout the UK to compare the incidence of consultations (using the self-controlled case series method) for events compatible with a vaccine reaction in children [16]. Our study used a similar principle to the UK study even though the data sources are quite different. For our study, we used a linked dataset since there was no one database that had vaccination record and GP encounters similar to the UK’s GPRD. The other overseas studies from New Zealand have explored reactogenicity using convenience samples of general practices that had received stocks of influenza vaccines, and surveyed parents of children under five years of age who were vaccinated [22,23]. These studies found that compared to other trivalent seasonal influenza vaccines (e.g. Sanofi Pasteur TIV), CSL TIV was associated with higher rates of febrile reactions and children were more likely to seek medical advice for fever from general practitioners [22,23]. Both these New Zealand studies used

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self-reported measures while our study was based on actual general practice encounters following receipt of an influenza vaccine, which is a major strength of our study. However, there are several potential limitations in our study including the timeliness of the data and transfer of influenza vaccination data from general practice software systems to the ACIR [24]. Another limitation is that sometimes the brand names are not reported and the accuracy of those reported is unknown. We were also unable to determine the reason for the GP encounter and a vaccine-related encounter was assumed given the proximity in time to vaccine administration. However, encounter rates will include an unknown background rate of encounters for other reasons. This background rate could vary seasonally with the prevalence of respiratory and other viral infections, although in this linked dataset, all children who were known to have received an influenza vaccine were included in the study. Also, a severe but rare acute adverse events may not be detected unless it is associated with more common vaccine reactions. There also appears to be geographic differences between GP encounter rates in WA and elsewhere. This may be due to a variability in GP encounter reporting including differences in distribution of immunization providers across regions, though general practitioners are the most common providers at national level [25]. The proportion of non GP providers varies from 76% in the Northern Territory, to less than 20% in NSW and Queensland, with intermediate proportions in other regions [25]. The majority of general practitioners (GPs) are private practitioners, but most of their services are funded through Medicare, an Australian Government program [26]. Despite the potential limitations, our method of evaluating reactogenicity following receipt of a vaccine has some unique strengths. All Australian children who were reported to the ACIR as having received an influenza vaccine from a general practice setting during the specified time period, have been included in this national linkage study. Hence, a large and representative number of encounters were available for analysis, giving good power to detect an effect and allowing for an unbiased retrospective comparative analysis. In conclusion, new vaccines and vaccination programs require timely interventions and evaluation. Addition of new vaccine brand names to practice management software and ACIR notification forms in a timely manner, and educating providers about the importance of, and correct way to, notify influenza vaccination to the ACIR would further improve the utility of this method. The methodology reported here could be used for signal detection of early-onset adverse events if the vaccine and general practice data are readily accessible, and has the potential for use in various health settings. Notably, the use of linked data from passive surveillance systems such as general practice encounter data and ACIR provide an enormous opportunity for not only monitoring uptake of vaccines but also for alerting to any early increase in reporting of adverse events following immunization.

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General practice encounters following seasonal influenza vaccination as a proxy measure of early-onset adverse events.

In 2010, use of seasonal trivalent influenza vaccine (TIV) in children ...
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