Safety of influenza vaccines
Common responses to vaccination
Influenza vaccine is generally well tolerated.
Common responses associated with inactivated influenza vaccines in adults and children include pain, redness and/or swelling at the site of injection. Local responses are almost always mild. Systemic events such as headache, muscle aches and fatigue may occur in adults. Fever, irritability and loss of appetite are more likely to occur in children. These are generally mild and usually resolve after a day or so. Systemic events may appear influenza-like. However, the influenza vaccines currently used in New Zealand do not contain live viruses and cannot cause the disease
Serious events associated with influenza vaccine
The most significant serious adverse event associated with influenza vaccination is anaphylaxis, a serious allergic response that usually comes on within minutes of receiving the vaccine. This occurs around once in a million influenza vaccine doses.
With the possible exceptions of Guillain-Barré syndrome (refer below) and that side effects related to some new immune-stimulant cancer treatments could be triggered, other serious adverse events are no more likely to occur in individuals who are vaccinated compared with those who are unvaccinated.
Guillain-Barre Syndrome and influenza vaccination
Guillain-Barré syndrome (GBS) has an annual incidence of around 1–4 cases per 100,000 people worldwide.
During a swine influenza vaccination campaign in the United States in the 1970s, an increase in GBS was observed in vaccine recipients (around one case per 100,000 vaccinations) and the vaccination campaign was halted and surveillance of GBS expanded.
Epidemiological studies since then have suggested either no increased risk or a possible slight increase in risk of around one case per million adult influenza vaccinations. A recent meta-analysis of these studies identified a small increase in the risk of GBS following influenza vaccination. However, studies have also identified that the risk of GBS following an episode of influenza-like illness is significantly higher than the risk following influenza vaccination, especially in older adults. This highlights the importance of balancing the potential risks of disease with the potential risks and benefits of influenza vaccination to make an informed decision.
Febrile events following influenza vaccination
Fever is a common adverse event in children after vaccination. Convulsions associated with fever can occur in susceptible children. Around 3–8 children in 100 aged under 7 years will experience a febrile convulsion, most likely when aged between 16 and 30 months.
In one study, children aged 6–23 months were two to three times more likely to develop a fever of 38°C–39°C during the first 24 hours after receiving influenza and PCV13 (PREVENAR 13®) vaccines at the same visit compared with children who
received the vaccines on separate days.
Parents/guardians whose children are recommended to receive both influenza vaccine and PCV13 should be advised of the possible increase in risk of fever following concurrent administration of these vaccines. Separating administration of these vaccines by two days can be offered, but is not essential.
For the PREVENAR 13® data sheet please refer to the Medsafe website www.medsafe.govt.nz.
Reporting adverse events following influenza vaccination
Healthcare professionals/vaccinators are professionally and ethically responsible for reporting any serious or unexpected adverse events after the administration of all medicines, including the influenza vaccine, regardless of whether or not they consider the event to have been caused by the vaccination.
Information should include:
• vacinee’s details
• the vaccine administered
• vaccine batch number
• date of onset of symptoms
• type and duration of adverse event
• treatment required
• outcome if known but do not delay reporting while waiting outcome information
Some providers are able to report events through their practice management system. Reports can be completed online (nzphvc.otago.ac.nz), or the form can be downloaded and printed using the above link, completed and mailed to:
The Medical Assessor
Centre for Adverse Reactions Monitoring
University of Otago Medical School
PO Box 913, Dunedin 9054
or faxed to: (03) 479 7150