Why URTIs Can Still Occur After Influenza Vaccination
The influenza vaccine specifically protects only against influenza virus strains included in the vaccine formulation, not against the numerous other viral and bacterial pathogens that cause upper respiratory tract infections. 1
The Vaccine's Specific Protection
The influenza vaccine contains three virus strains (two type A and one type B) representing the influenza viruses predicted to circulate in the upcoming season. 2 This means the vaccine provides protection exclusively against these specific influenza strains and closely related variants, not against other respiratory pathogens. 2
When vaccine and circulating influenza strains are well-matched, the vaccine prevents influenza illness in approximately 70%-90% of healthy adults under 65 years. 2 However, this protection is highly strain-specific and does not extend to other causes of URTIs. 2
Multiple Pathogens Cause URTIs
Upper respiratory tract infections are caused by numerous different pathogens beyond influenza, including:
- Other respiratory viruses (rhinovirus, coronavirus, respiratory syncytial virus, parainfluenza, adenovirus, human metapneumovirus) 1, 3
- Bacterial pathogens 1
- The vaccine provides no protection against these non-influenza pathogens 1
The American Academy of Otolaryngology-Head and Neck Surgery confirms that viral URTIs typically present with cough, sneezing, rhinorrhea, sore throat, and nasal congestion—symptoms that can be caused by any respiratory pathogen, not just influenza. 1
Vaccine Limitations in Certain Populations
Even for influenza-specific protection, the vaccine has important limitations:
Elderly persons and those with chronic diseases may develop lower postvaccination antibody titers than healthy young adults and can remain susceptible to influenza-related upper respiratory tract infection. 2 In nursing home populations, vaccine effectiveness in preventing influenza illness itself often ranges only from 30%-40%, though it remains 50%-60% effective in preventing hospitalization and 80% effective in preventing death. 2
Vaccine-Strain Mismatch
The vaccine's effectiveness depends critically on the degree of similarity between vaccine strains and circulating viruses. 2 When there is antigenic mismatch—which occurs when influenza viruses undergo antigenic drift or when predictions about circulating strains prove inaccurate—vaccine effectiveness decreases substantially. 4, 5
Common Pitfall to Avoid
Do not assume that influenza vaccination provides broad protection against all respiratory infections. The vaccine is highly specific for influenza strains and does not reduce susceptibility to the many other pathogens causing URTIs. 1 Patients should understand that vaccination reduces their risk of influenza specifically, but they can still develop URTIs from other causes throughout the respiratory illness season. 1
The vaccine cannot cause influenza because it is made from inactivated viruses, so any URTI symptoms developing after vaccination are either coincidental infections from other pathogens or, rarely, mild local reactions to the vaccine itself. 2