Discussion

The New Zealand National Immunisation Register provides a comprehensive record where children are registered at birth. Less than 1 per cent of parents and guardians choose to opt out of this process. The National Immunisation Register is updated directly by recognised immunisation providers following an immunisation event.¹⁵

H Influenzae B vaccination has been part of the National Immunisation Schedule since 1994, and the pneumococcal conjugate vaccination was added to the schedule in June 2008. It is of no surprise that once the pneumococcal conjugate vaccination became fully funded, the vaccination rate improved markedly from 44.1 per cent before June 2008 to 97.2 per cent after June 2008.

The overall immunisation coverage was low with only 10.3 per cent receiving a complete schedule of H Influenzae, S Pneumoniae and influenza vaccine.

There are limited studies on vaccination compliance in cochlear implant patients. Piotrowska et al. observed a 49.2 per cent streptococcal pneumonia vaccination rate despite the vaccine being mandatory and publicly funded for cochlear implant patients in Poland.^{Reference Piotrowska, Paradowska-Stankiewicz and Skarzynski16} A recent Spanish study showed that only 5.71 per cent of the cochlear implant patients had 100 per cent compliance to their vaccination schedule. Their paediatric population had pneumococcal conjugate and H influenzae B vaccine compliance rates of more than 90 per cent.^{Reference Fernandez-Prada, Madronal-Menendez, Martinez-Ortega, Ramos-Martin, Fernandez-Noval and Huerta-Gonzalez17} This is comparable with our findings following the introduction of additional funding of vaccinations for cochlear implant recipients.

In the USA, Carpenter et al. found improvement in pneumococcus vaccination rates ranging from 49 per cent to 99 per cent across various population groups following various methods of information dissemination and reminders.^{Reference Carpenter, Limb, Francis, Gottschalk and Niparko18} Volsky et al. observed a 70 per cent pneumococcal vaccination compliance. The most important factor appeared to be encouraging patients to vaccinate prior to surgery.^{Reference Volsky, Ballard and Moody-Antonio19}

The majority of meningitis cases following cochlear implantation reported in the literature were related to S pneumoniae and H influenzae type B, two of the most common causative agents in acute bacterial otitis media. Acute otitis media is the most likely cause for meningitis beyond the first 30 days following cochlear implantation because of bacterial spread along the pathway of the electrode.^{Reference Rubin and Papsin20} Seasonal influenza vaccine has been shown to reduce the incidence of acute otitis media.^{Reference Clements, Langdon, Bland and Walter21,Reference Heikkinen, Ruuskanen, Waris, Ziegler, Arola and Halonen22} Pneumococcal infections predominantly affect children younger than 2 years of age and adults above the age of 60 years.^{Reference Breiman, Spika, Navarro, Darden and Darby23} These two groups account for the overwhelming majority of cochlear implant recipients.

Our first meningitis case occurred within three weeks of cochlear implant surgery, and it was secondary to a non-typeable H influenzae infection. This is suggestive of a surgical or patient-related factor as opposed to acute otitis media. The patient also had an inner ear malformation. Unfortunately, an effective vaccine against non-typeable H influenzae is not currently available. Our second patient required a cochlear implant because of bilateral profound sensorineural hearing loss following recurrent streptococcus pneumonia meningitis. This patient had an associated inner ear dysplasia.

Cost is a well-recognised barrier to access to healthcare. Free vaccination is provided to New Zealand residents according to the National Immunisation Schedule and, as expected, our study showed a clear improvement in compliance with pneumococcal conjugate vaccination following additional funding for cochlear implant patients as a special group and its subsequent addition to the National Immunisation Schedule. However, we did not observe a similar increase in the uptake of yearly influenza and pneumococcal polysaccharide vaccination. As such, this raises the possibility of a lack of awareness of vaccination guidelines for cochlear implant recipients. The findings of this study are different to those observed in our adult cohort¹² as the majority of adult cochlear implant recipients received their childhood vaccinations before H influenzae B and pneumococcal conjugate vaccination were added to the National Immunisation Schedule. Compared to adults, our paediatric patients had lower coverage with vaccines usually indicated for adults over the age of 65 years (seasonal influenza and pneumococcal polysaccharide vaccination). Individuals under the special group provision, including cochlear implant recipients, have not been extensively studied for their compliance with recommended vaccines. The overall influenza vaccine uptake for adults older than 65 years was only 56 per cent in 2018 despite being eligible for funded vaccines.^{Reference Nowland, Murfitt and Turner24} A survey of 101 pregnant women carried out at Wellington Hospital, New Zealand, showed a 76 per cent influenza vaccine uptake rate. The primary reason for vaccination was neonatal protection. The most common reasons given for non-compliance were not receiving information about the vaccine or not receiving the vaccine.^{Reference Andre, Gavrilov, Graham, Scheck, Chandler and Hunter25}

The literature suggests that a lack of knowledge on influenza disease and the vaccine represents the biggest barrier to vaccination. This revolves around concerns about vaccine safety, doubts about its effectiveness and the misconception that influenza is not a serious condition.^{Reference Naleway, Henkle, Ball, Bozeman, Gaglani and Kennedy26,Reference Kadi, Atif, Brenet, Izoard and Astagneau27} Seasonal influenza can cause severe illness and even death in high-risk individuals. Unfortunately, it is often confused with the common cold despite being responsible for 490 600 hospitalisations and 34 200 deaths in the USA during the 2018–2019 season.²⁸

The use of reminders and recall systems has been associated with an improvement in influenza vaccination rates.^{Reference Cooper and Walton-Moss29} In addition, some cochlear implant programmes have recruited an infectious disease vaccine specialist to help address their low compliance, and this has resulted in a substantial improvement in compliance.^{Reference Jin, Tellez, Chia, Lu, Chadha and Pauwels30} These are options that we are considering.

An underestimation of the true impact of funded vaccines is a potential limitation of this study because we excluded children born before the National Immunisation Register was introduced in 2005. Most of these children were not included in the data available on H influenzae B coverage which is usually administered in the first 15 months of life. H influenzae B vaccination has been part of the National Immunisation Schedule since 1994; therefore, these children were probably vaccinated before 2005, but this was not recorded. On the other hand, funding for pneumococcus and influenza vaccination was initiated in 2008 and 2015, respectively, and some are missing out on these vaccines.