Doctors Explain Flu Shot Timing and Protection Guidance

Health experts are outlining when people should receive annual influenza vaccines and how vaccination reduces serious illness risks as flu season approaches. Doctors from Massachusetts General Hospital and the University of Nebraska Medical Center explained symptoms, complications, and vaccine timing guidance.

Influenza causes respiratory symptoms that can overlap with COVID-19 and other infections, making testing important for diagnosis, according to experts. Many people recover within days to two weeks, but some develop severe complications.

Dr. Sandra Nelson, the inpatient clinical director of the Division of Infectious Diseases at Massachusetts General Hospital, described the typical onset of influenza symptoms.

"with an abrupt onset of symptoms," says Dr. Sandra Nelson, the inpatient clinical director of the Division of Infectious Diseases at Massachusetts General Hospital.

Nelson warned that describing influenza as a minor illness can overlook serious health effects, including pneumonia, inflammation of the heart or brain, and sepsis.

"just the flu," says Dr. Sandra Nelson, the inpatient clinical director of the Division of Infectious Diseases at Massachusetts General Hospital.

She explained that vaccine protection can vary depending on age, health conditions, and how closely the vaccine matches circulating viruses.

"In some years, effectiveness against infection may be as low as 30%, and in other years as high as 80%," says Dr. Sandra Nelson, the inpatient clinical director of the Division of Infectious Diseases at Massachusetts General Hospital.

Nelson emphasized that preventing severe outcomes is a key measure of vaccine value beyond preventing infection.

"is that the vaccine prevents severe outcomes like hospitalization or death." says Dr. Sandra Nelson, the inpatient clinical director of the Division of Infectious Diseases at Massachusetts General Hospital.

The doctor also discussed immunity development after vaccination and the importance of timing shots before flu activity increases.

"it can take a few weeks following vaccination for immunity to develop, and we want to be fully protected before the onset of flu season," says Dr. Sandra Nelson, the inpatient clinical director of the Division of Infectious Diseases at Massachusetts General Hospital.

Nelson said vaccination remains the main preventive tool for protecting individuals and their loved ones.

"vaccination remains extremely safe and is the best tool that we have to keep ourselves and our loved ones healthy." says Dr. Sandra Nelson, the inpatient clinical director of the Division of Infectious Diseases at Massachusetts General Hospital.

Dr. David Brett-Major, an epidemiologist at the University of Nebraska Medical Center’s College of Public Health, highlighted groups facing higher risks from influenza complications.

"there are many groups of people at risk for poor outcomes," says Dr. David Brett-Major, an epidemiologist at the University of Nebraska Medical Center’s College of Public Health.

Brett-Major noted that health care workers and people in certain medical risk groups require particular attention during flu season.

"Health care workers, including those who work in long-term care facilities and nursing homes, are also at increased risk," says Dr. David Brett-Major, an epidemiologist at the University of Nebraska Medical Center’s College of Public Health.

He added that vaccination can help reduce illness severity among infected people.

"shorten the amount of time that those who are infected feel sick," says Dr. David Brett-Major, an epidemiologist at the University of Nebraska Medical Center’s College of Public Health.

Brett-Major also noted that flu seasons can continue into spring months.

"Most flu seasons reach late March and into April," says Dr. David Brett-Major, an epidemiologist at the University of Nebraska Medical Center’s College of Public Health.

The Centers for Disease Control and Prevention reported that children remain among the groups vulnerable to severe flu outcomes. CDC modeling estimated 790 child deaths from influenza during the 2024–2025 season.

"about 90% occurred in children who were not fully vaccinated against flu." says the Centers for Disease Control and Prevention.

The CDC recommends annual flu vaccination for everyone 6 months and older, with rare exceptions. September or October is the preferred vaccination window for most people, ideally before the end of October.