Abstract
The seasonal influenza vaccine (SIV) has been administered to the public for many years in Aotearoa New Zealand; however, safety concerns and fear of possible adverse events following immunisation (AEFI) remain an issue of interest. Understanding the spectrum and volume of AEFIs reported within New Zealand can be used to inform and support the understanding of the risks associated with vaccination within the context of the New Zealand health system. The New Zealand Pharmacovigilance Centre houses the Centre for Adverse Reaction Monitoring Programme (CARM), which receives and analyses adverse reactions to medications and vaccines. This study comprised a series of retrospective analyses of AEFIs to both the SIV and the COVID-19 vaccines received by CARM.
The first study described the AEFI reporting patterns for SIV over ten years (2010-2019) to understand the trends in the demographics of those who experienced an AEFI, the demographics of those who reported AEFIs, and the pattern of reactions experienced. Over the 10-year period, 2,788 reports were received by CARM. Most of the reports, 76% (2,129) were non-serious; a higher proportion 46% (1,274) were from older adults, females 73% (2,039), and individuals who identified as Europeans 80% (2,241). The reports primarily originated from healthcare workers, specifically nurses 59% (1,653). The most frequently reported AEFIs were local (injection site inflammation, arm pain, injection site pain) and systemic (fever, headache, vomiting) events, which in total represented 30% (1,980/6,557) of all reports.
The second study, an extension to the first study, described the impact of the COVID-19 pandemic on seasonal influenza vaccination adverse event patterns during the pandemic by evaluating the AEFI reporting patterns related to SIV before (2017 to 2019) and during (2020 to 2022) the COVID-19 pandemic. Using the vaccine administration data from the NIR, it was possible to calculate the crude rate of reporting. A comparison of the SIV AEFI crude reporting rates before and during the COVID-19 pandemic showed variations in the reporting rates per year, with the highest rates in 2018 (40/100,000 administered doses) and 2021 (47/100,000 administered doses). There were differences in the age-specific crude reporting rates; specifically, the younger age groups (0-9, 20-29, 30-39, 40-49) had higher crude reporting rates than the older adults (50-59, 60-69, 70+). Females also showed a higher crude reporting rate than males each year, especially in 2018 (54/100,000 doses) and 2021 (63/100,000 doses). Europeans and Māori reported AEFI at a comparable rate; in 2018: 41/100,000 doses and 43/100,00 doses; in 2019: 33/100,00 doses and 34/100,000 doses; and in 2020: 26/100,000 doses and 24/100,000 doses. The most frequently reported AEFIs before the pandemic were local (injection site inflammation, injection site pain, arm pain) and systemic ( headache, fever, nausea) events, which represented 27% (505/1,905) of the total reports. Similarly, during the pandemic, the most frequently reported AEFIs were local (injection site inflammation, injection site pain, arm) and systemic (headache, fever, nausea) events, which represented 27% (636/2,316) of the total reports.
The third study described the adverse events experienced and reported for the Pfizer/BioNTech mRNA COVID-19 vaccine. This study investigated AEFI reports from 20 February 2021 to 31 December 2022, and during that time, a total of 64,956 reports were made, representing a rate of 543 people per 100,000 doses administered. The highest number of reports (10,433) was recorded in September 2021 (which aligns with the highest Comirnaty dose administration period). The findings showed a higher proportion of reports in young adults (30-39 years, 22%, 14,030) and females (69%, 45,086). The most frequently reported AEFIs were systemic (headache, nausea, lethargy), ISRR (dizziness, chest discomfort) and local (injection site pain), which represented 40% (93,983/236,842) of the total reports. As anticipated, given the nature of the COVID-19 vaccine, there were more reports of a clinically significant nature, including myocarditis and pericarditis.
The AEFI profile of the seasonal influenza vaccine in New Zealand is comparable with the global SIV profile. Generally, the SIV studies showed that most AEFI reports were non-serious, and there were more AEFI reports in older adults, females, and individuals who identified as Europeans. However, while older adults represented the largest group by proportions, the younger population represented the highest reporting rates based on the SIV vaccine administration data. Europeans and Māori are affected by AEFIs at comparable rates. The AEFI reports primarily originated from healthcare workers. The specific reported AEFIs for the SIV were primarily mild and self-limiting and included events such as injection site inflammation, injection site pain, arm pain, fever and headache. The most frequently reported AEFIs for the Pfizer/BioNTech COVID-19 vaccine (Comirnaty) overall were dizziness and headache, but reports of more clinically significant reactions also occurred. Of note, reports of medication errors, which increased during the pandemic period, may reflect the health service delivery and rapid introduction of new vaccinators.
This thesis has determined the underlying profile of AEFIs in terms of both demographics and reactions and highlighted the dynamic nature of AEFI reporting, which varied over time depending on the prevailing circumstances. These circumstances included funding eligibility, the change and introduction of new vaccines, gender-based reporting dynamics, and changes in health system delivery. The extent to which these factors influence AEFI reporting should be investigated in future studies.