Published: 2 March 2017
Prescriber Update 38(1): 4-5
Seasonal influenza has a substantial impact on public health. The annual influenza-related hospitalisation rate in New Zealanders over 80 years of age is 327.8 per 100,000 and under 1 year of age is 244.5 per 100,0001.
The Southern Hemisphere Influenza Vaccine Effectiveness, Research and Surveillance (SHIVERS) project and the Institute of Environmental Science and Research Limited (ESR) monitors the impact of influenza infection and vaccination in New Zealand. The incidence rate of influenza deaths was calculated at 0.8 per 100,000 in 2015, but this is likely to be an underestimate2.
The effectiveness of influenza vaccine is around 50%, when measured by a reduction in hospitalisation due to influenza infection (using a case test- negative design, a type of case-control study to estimate influenza vaccine effectiveness). However, efficacy is lower in older people2,3.
To reduce hospitalisation and other complications, seasonal influenza vaccine is offered free to those at higher risk of influenza complications (www.influenza.org.nz/eligibility-criteria) and by many employers.
In 2016, the Centre for Adverse Reactions Monitoring (CARM) received 212 reports of 527 adverse events following immunisation (AEFI) with seasonal influenza vaccine (Table 1). Some reports contained more than one AEFI.
The most commonly reported events were injection site inflammation (47 reports), arm pain (25), dizziness (23) and headache (21).
Seven (3%) of the influenza vaccine-related reports were considered serious. A serious adverse event is determined by CARM according to internationally agreed criteria (ie, results in death or is life-threatening, causes or prolongs hospitalisation, results in persistent or significant disability/incapacity or is a congenital abnormality).
In one report, the patient was reported to have died of a myocardial infarction following influenza vaccination. The death was considered unlikely to be due to the vaccination.
The majority of reports were submitted by nurses (80%), followed by GPs (14%) and pharmacists (5%).
Table 1: Number of reports of AEFI received by CARM and number of influenza vaccine doses distributed, 2012–2016
|Reports of adverse events following influenza vaccination||193||290||253||241||212|
|Influenza vaccine doses distributed*||1,000,600||1,253,600||1,206,573||1,211,152||1,245,934|
|Estimated reporting rate per 100,000 doses||19.3||23.1||21.0||19.9||17.0|
*The number of doses distributed is not equal to number administered.