Influenza vaccination can significantly reduce the risk of flu infections and complications. However, some people may still develop influenza even after getting vaccinated. This can lead to questions about vaccine effectiveness and whether vaccination is still beneficial. This article explains why flu infections can still occur post-vaccination, what influences vaccine effectiveness, and why getting vaccinated remains a necessary step in flu prevention.
Can Influenza Occur After Vaccination?
Although flu vaccines provide significant protection, several factors can contribute to post-vaccination infections.
Strain Mismatch: Flu vaccines are formulated based on predictions of which strains will circulate in an upcoming season. However, influenza viruses mutate frequently, and if the dominant strain circulating in the community is different from the strains included in the vaccine, immunity may be reduced. Even with a mismatch, the vaccine can still offer partial protection, reducing the severity and duration of symptoms.
Time Required for Immunity: The flu vaccine does not provide immediate protection. It takes approximately two weeks for the immune system to generate a sufficient response to the vaccine. During this period, individuals remain susceptible to infection, especially if flu activity is high. This is why early vaccination, before flu season peaks, is generally recommended.
Weakened Immune Response: Certain individuals, such as older adults, young children, and those with chronic health conditions, may have a weaker immune response to the vaccine. This can lead to reduced protection, making them more likely to contract the flu even after vaccination. However, in these cases, the vaccine still lowers the risk of severe illness, hospitalisation, and complications.
Other Respiratory Viruses: Flu-like symptoms can also result from other respiratory infections, such as the common cold or respiratory syncytial virus (RSV). Since symptoms can overlap, only a laboratory test can confirm influenza. Many individuals may assume they have the flu when in fact they’re infected with another virus not targeted by the flu vaccine.
Does the Flu Vaccine Still Provide Benefits?
Despite the possibility of post-vaccination flu infections, the flu vaccine remains an effective tool for reducing the overall burden of influenza.
Reduced Severity of Illness: Even if a vaccinated person contracts the flu, symptoms tend to be milder compared to those in unvaccinated individuals. Studies have shown that flu vaccination reduces the likelihood of severe complications, hospitalisation, and death, particularly in high-risk groups.
Lower Transmission Rates: Vaccination helps slow the spread of influenza within communities. When more people are immunised, there are fewer opportunities for the virus to circulate, providing indirect protection to those who cannot receive the vaccine, such as infants under six months of age.
Protection Against Multiple Strains: The flu vaccine is designed to protect against several strains of influenza. While one strain may dominate a season, other strains can still circulate, and the vaccine offers protection against them. This broad coverage helps prevent infections even in years with partial strain mismatches.
Annual Protection: Annual vaccination helps protect against the most recently circulating strains, which is important because immunity from previous years may wane, and the virus constantly evolves. Skipping yearly flu shots increases the risk of infection due to waning immunity from previous vaccinations.
How to Further Reduce the Risk of Influenza
While vaccination is a key preventive measure, additional steps can help minimise the risk of infection.
Practising Good Hygiene: Regular handwashing, avoiding touching the face, and disinfecting frequently touched surfaces can limit the spread of influenza and other respiratory viruses.
Avoiding Close Contact with Sick Individuals: Steering clear of people who exhibit flu symptoms and maintaining physical distance in crowded places can lower the risk of exposure.
Maintaining Immune Health: Maintaining a healthy diet, getting sufficient sleep, staying hydrated, and managing stress can support immune function, improving the body’s ability to fight infections.
Seeking Medical Advice When Necessary: High-risk individuals should consult a doctor promptly if flu symptoms appear, as antiviral medications may be prescribed to shorten illness duration and reduce complications.
Conclusion
Although it is possible to get influenza after vaccination, the flu vaccine still provides considerable benefits by reducing infection risk, lowering illness severity, and helping control flu spread. Annual vaccination, combined with good health practices, provides the most effective protection against seasonal influenza.
Schedule a consultation with Dr Adrian Mondry to discuss flu vaccination and additional measures to stay protected throughout the flu season.
