Influenza, or the flu, is a contagious respiratory illness caused by viruses, leading to symptoms like fever, body aches, cough, and sore throat. It is possible to contract the flu more than once within the same season.
The Possibility of Re-infection
Getting the flu more than once in a single season typically occurs because different strains of influenza viruses circulate simultaneously. While contracting one strain usually confers immunity to that specific variant, it leaves an individual susceptible to other circulating strains. This re-infection can happen even within a relatively short timeframe, such as a month, if exposure to a different strain occurs. The immune system’s response is highly specific to the viral strain encountered, so protection developed against one strain does not extend to others.
Different Flu Strains and Immunity
Influenza viruses are diverse and constantly evolve. Types A and B are the main causes of seasonal epidemics in humans. Influenza A viruses are further categorized into subtypes based on surface proteins, such as H1N1 and H3N2, while Influenza B viruses are classified into two main lineages.
Flu viruses constantly change through two main processes: antigenic drift and antigenic shift. Antigenic drift involves small, gradual changes in flu virus genes, altering their surface proteins. These minor changes can accumulate, making it harder for the immune system to recognize the virus.
Antigenic shift is a sudden, major alteration in influenza A viruses, often when two different strains combine to form a new subtype. This can result in little pre-existing immunity in humans.
Immunity from a previous infection or vaccination is specific to the particular strain encountered. For example, an H1N1 infection does not provide protection against an H3N2 or Influenza B virus. The body creates antibodies tailored to specific viral components, and if these components change sufficiently, those antibodies may no longer be effective.
Distinguishing Flu from Other Illnesses
People sometimes mistakenly believe they have contracted the flu multiple times when they have, in fact, experienced different respiratory illnesses. Conditions such as the common cold, Respiratory Syncytial Virus (RSV), and strep throat can present with symptoms that overlap with the flu.
The common cold typically presents with milder symptoms that develop gradually, often including a runny or stuffy nose and sneezing, with fever being less common. In contrast, the flu usually has a sudden onset with more intense symptoms like high fever, chills, body aches, and fatigue.
RSV can also cause fever, cough, and runny nose, but is more commonly associated with wheezing, especially in young children and older adults. Strep throat, a bacterial infection, primarily causes a sudden, severe sore throat, often without a cough or nasal congestion, and may involve visible white patches on the tonsils.
Given these symptom similarities, a definitive diagnosis often requires laboratory testing. Relying solely on symptoms can lead to misidentification, causing someone to think they had the flu repeatedly when they were actually infected by different viruses.
Preventing Multiple Flu Episodes
Preventing multiple flu episodes involves a multi-faceted approach, with annual vaccination being a primary strategy. The flu vaccine protects against the influenza viruses predicted to be most prevalent, helping reduce the risk of illness, hospitalization, and severe outcomes.
Beyond vaccination, maintaining good hygiene practices plays a role in reducing the spread of respiratory illnesses. Frequent handwashing with soap and water, or using alcohol-based hand sanitizers, is effective. Avoid touching your eyes, nose, and mouth.
Cover coughs and sneezes with a tissue or into your elbow. Staying home when sick prevents transmitting the virus to others, reducing overall circulation of influenza and other respiratory pathogens.