Available Vaccines
Influenza
Introduction
Influenza is caused by the Influenza virus, a segmented RNA virus from the Alphainfluenzavirus Genus and Orthomyxoviridae family. Of the 4 influenza subtypes, Influenza A and B viruses cause all the human infection. The strains currently circulating globally are the Influenza A H1N1pdm09, Influenza A H3N2 and Influenza B. The influenza virus is normally transmitted via droplet inhalation, direct close contact as well as contaminated surfaces.
Following an incubation period of around 2 days, influenza typically begins suddenly with fever, sore throat, headache, muscle aches, chills, fatigue, and loss of appetite, followed by a runny nose and dry cough. While most otherwise healthy individuals recover within 3 to 7 days, fatigue can linger for weeks. Notably, individuals are contagious even before symptoms appear, starting one day prior to symptoms onset and can continue spreading the virus for up to 7 days after symptoms begin. In older adults, influenza may not present with typical symptoms like fever. Instead, it may manifest as confusion, loss of appetite, or general weakness, making diagnosis more challenging. Additionally, up to 75% of individuals may have asymptomatic infections, yet still transmit the virus to others.
Influenza affects around 5–15% of adults globally each year. The risk of severe influenza complications is highest in infants, the elderly, and individuals with chronic health conditions. Serious outcomes include worsening of underlying lung or heart diseases (such as COPD, asthma, or heart failure) and secondary bacterial pneumonia, most commonly caused by Streptococcus pneumoniae, Staphylococcus aureus, or Haemophilus influenzae.
Table 13.1 Vaccines Registered in Malaysia
Table 13.2 High-risk Group in Malaysia
Implications for Healthcare Workers (HCWs)
All healthcare workers should receive annual influenza vaccination to protect themselves and prevent transmission to vulnerable patients, as it is a critical measure for patient safety and infection control in healthcare settings.
Evidence for Safety and Effectiveness
Inactivated influenza vaccines (IIVs) have an excellent safety profile and are well tolerated by recipients of all ages, including individuals with underlying conditions and pregnant women. Mild adverse reactions are frequent but self-limiting, lasting no more than 1 to 2 days. In adults and older children, mild pain at the injection site is common (60–80% of recipients); systemic symptoms include low-grade fever (2–10%), malaise, headache, myalgia and fatigue.
A meta-analysis of 31 studies found trivalent inactivated influenza vaccines (TIV) to be 59% effective in healthy adults aged 18–65. However, data on adults over 65 are limited, with lower effectiveness observed, though studies suggest it still helps reduce illness severity, complications, and mortality.
High-dose, recombinant and adjuvanted vaccines have demonstrated a higher vaccine efficacy or effectiveness against symptomatic disease, with a slightly increased reactogenicity than standard inactivated vaccines in older adults.
References
- Hayward, A. C., Fragaszy, E. B., Bermingham, A., et al and Flu Watch Group. (2014). Comparative community burden and severity of seasonal and pandemic influenza: Results of the Flu Watch cohort study. The Lancet Respiratory Medicine, 2(6), 445–454. https://doi.org/10.1016/S2213-2600(14)70034-7
- Centers for Disease Control and Prevention. (2022). How influenza (flu) vaccines are made. U.S. Department of Health & Human Services. https://www.cdc.gov/flu/vaccine-process/index.html
- Erbelding, E. J., Post, D. J., Stemmy, E. J., et al. (2018). A universal influenza vaccine: The strategic plan for the National Institute of Allergy and Infectious Diseases. Journal of Infectious Diseases, 218(3), 347–354. https://doi.org/10.1093/infdis/jiy103
- Centers for Disease Control and Prevention. (2024). Influenza (flu) vaccination and egg allergy. https://www.cdc.gov/flu/prevent/egg-allergies.htm
- Centers for Disease Control and Prevention. (2024). Prevention and control of seasonal influenza with vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP). https://www.cdc.gov/mmwr/volumes/73/rr/rr7305a1.htm
- Isahak, I., Mahayiddin, A. A., & Ismail, R. (2007). Effectiveness of influenza vaccination in prevention of influenza-like illness among inhabitants of old folk homes. The Southeast Asian Journal of Tropical Medicine and Public Health, 38(5), 841–848. https://pubmed.ncbi.nlm.nih.gov/18041300/
- Mustafa, A. N., Gessner, B. D., Ismail, R., Yusoff, A. F., Abdullah, N., Ishak, I., Abdullah, N., & Merican, M. I. (2003). A case-control study of influenza vaccine effectiveness among Malaysian pilgrims attending the Haj in Saudi Arabia. International Journal of Infectious Diseases : IJID : official publication of the International Society for Infectious Diseases, 7(3), 210–214. https://doi.org/10.1016/s1201-9712(03)90054-3
- Osterholm, M. T., Kelley, N. S., Sommer, A., & Belongia, E. A. (2012). Efficacy and effectiveness of influenza vaccines: a systematic review and meta-analysis. The Lancet. Infectious diseases, 12(1), 36–44. https://doi.org/10.1016/S1473-3099(11)70295-X
- World Health Organisation (May 13, 2022). Vaccines against influenza: WHO Position paper-May 2022. Weekly epidemiological record; 97(19):185-208. https://www.who.int/publications/i/item/who-wer9719
- World Health Organisation (February 28, 2025). Recommended composition of influenza virus vaccines for use in the 2025-2026 northern hemisphere influenza season. https://www.who.int/teams/global-influenza-programme/vaccines/who-recommendations