Flu vaccination cannot cause influenza and can still reduce severe illness even when circulating strains make the shot less effective at preventing infection, according to guidance from University of Rochester Medical Center specialists.
Mild soreness, redness, fatigue or a low fever can occur for a day or two after vaccination as the immune system responds. The vaccine itself cannot give a person the flu, and a serious illness that begins after the shot is more likely to have another cause, URMC said.
Infectious disease specialists analyze flu patterns each year to decide which strains should be included in the vaccine. A vaccinated person may still become infected, but symptoms are often milder and recovery can be faster than without vaccination.
URMC infectious disease physician Angela Branche said the 2025-26 vaccine offered limited protection against infection, particularly from circulating influenza A strains. She still recommended vaccination because it can lower the risk of hospitalization, complications and severe disease.
Vaccines build immune memory that works alongside protection from previous infections. Even partial immunity can help a person's body respond more effectively, the health system said.
URMC also advised that nausea and vomiting are not the symptoms most commonly associated with influenza. Cough, a runny nose, sore throat, high fever and significant body aches are more typical, though only a test can confirm an infection and clinicians may also diagnose flu from symptoms.
Doctors may prescribe antiviral medication such as Tamiflu for influenza. The treatment can reduce the duration and severity of illness when used appropriately, according to the guidance.
The ideal time for a flu shot is before the end of October, ahead of the usual seasonal peak, but vaccination later in the season can still be useful. Protection generally takes about two weeks to develop.
For people concerned about needles, FluMist nasal vaccine is approved for nonpregnant people ages 2 through 49. Patients should ask a health professional which vaccine is appropriate for their age and medical history.
FingerLakes1.com is the region’s leading all-digital news publication. The company was founded in 1998 and has been keeping residents informed for more than two decades. Have a lead? Send it to news@fingerlakes1.com.