What are the side effects of influenza vaccines?

Common side effects

• About 10 per cent of children (1 out of every 10) who have an influenza vaccine experience swelling, redness, pain at the injection site that lasts one or two days. 
• Between 1 per cent and 10 per cent of people (1–10 out of every 100) who have an influenza vaccine get a fever, headache, tiredness or lack of energy (malaise) or muscle aches (myalgia) that last one or two days. 

Rare side effects

• About 0.0014 per cent of children under two years (14 out of every 1,000,000) who have an influenza vaccine have a fit (febrile convulsion).^{1, 2} This happens when a baby or child’s temperature (fever) goes up suddenly. 

Very rare side effects

• About 0.0001 per cent of people (1 out of every 1,000,000) who get an influenza vaccine have a severe allergic reaction (anaphylaxis).³ 
• Less than 0.0001 per cent of people (1 out of every 1,000,000) who get an influenza vaccine get Guillian–Barré syndrome.⁴

What are the symptoms of influenza?

Usual symptoms 

• Children with influenza may get a fever, feel tired or lacking in energy (malaise), a headache, a dry cough, chills, muscle aches (myalgia), a runny nose and sneezing.
• Some babies and children may vomit or have diarrhoea (watery poo). 

Rare symptoms

• Children with influenza sometimes get acute bronchitis (swollen airways), croup (swelling in their voice box and windpipe that causes a bark-like cough), otitis media (ear infection that causes ear ache) and pneumonia (infected lungs).
• Children can experience a fit (febrile convulsion) from influenza infection. One study found about four in 100 children who were treated in hospital for influenza had a febrile convulsion.⁵

Very rare symptoms 

• Very rarely, children with influenza can get swelling (inflammation) in their heart muscle (myocarditis), the lining of their heart (pericarditis), or their brain (encephalitis). They can also get swelling in their liver and brain (Reye’s syndrome). 
• Very rarely, children can die from influenza. One study found between 2 and 4 children in every one million die from influenza.⁶ Because this number is hard to calculate accurately, the true number is likely higher. 

References

1. Australian Technical Advisory Group on Immunisation (ATAGI), Australian Immunisation Handbook. 2018, Australian Government Department of Health: Canberra. Available at: https://immunisationhandbook.health.gov.au

2. Hambidge, S.J., et al., Safety of Trivalent Inactivated Influenza Vaccine in Children 6 to 23 Months Old. JAMA, 2006. 296(16): p. 1990-1997. Available at: https://jamanetwork.com/journals/jama/article-abstract/203797

3. Australasian Society of Clinical Immunology and Allergy (ASCIA), Guidelines: vaccination of the egg-allergic individual. 2017, ASCIA: Sydney, Australia. Available at: https://www.allergy.org.au/hp//papers/vaccination-of-the-egg-allergic-individual

4. National Centre for Immunisation Research & Surveillance. Influenza vaccines - Frequently Asked Questions (NCIRS Fact sheet: March 2019). National Centre for Immunisation Research & Surveillance: Sydney, Australia. Available at: http://ncirs.org.au/sites/default/files/2019-06/Influenza_FAQs_31May2019_Final_0.pdf

5. Dawood, F.S., et al., Complications and associated bacterial coinfections among children hospitalized with seasonal or pandemic influenza, United States, 2003-2010.(Report). Journal of Infectious Diseases, 2014. 209(5): p. 686. Available at: https://academic.oup.com/jid/article/209/5/686/887068

6. Li-Kim-Moy, J., et al., Australian vaccine preventable disease epidemiological review series: Influenza 2006 to 2015. Communicable diseases intelligence quarterly report, 2016. 40(4): p. E482. Available at: https://www1.health.gov.au/internet/main/publishing.nsf/Content/cda-cdi4004f.htm