Influenza, or the flu, remains a persistent concern as we approach the 2024-2025 flu season. Let’s refresh our knowledge on this viral illness and understand how it might impact us this year.
Understanding Influenza (Flu)
Influenza is caused by influenza viruses, with subtypes A, B, C, and D under its umbrella. In humans, Influenza A and B are the most common, with Influenza A being the most diverse and widespread, as it can infect various animal species alongside humans. This diversity makes the virus more prone to mutations, potentially leading to new strains that can vary in contagiousness and severity from year to year. Influenza C can infect humans, dogs, and pigs, while Influenza D primarily affects cattle.
Common flu symptoms include:
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headaches
- Fatigue (tiredness)
- Fever or chills (though not everyone with the flu experiences fever)
- Vomiting and/or diarrhea (more common in children than adults)
Transmission of the flu is similar to other respiratory illnesses, such as COVID-19 or respiratory syncytial virus (RSV), occurring through airborne droplets when an infected person coughs, sneezes, or speaks. The virus can also survive on surfaces for extended periods, such as doorknobs, countertops, bottles, and smartphones.
Seasonal Patterns of the Flu
Flu season in the Northern Hemisphere typically spans from October to March, while in the Southern Hemisphere, it runs from April to September, corresponding to the fall-to-spring months, respectively. The reasons behind the seasonality of the flu are still not fully understood, but three main theories are proposed:
- Increased indoor interactions during colder months facilitate the spread of infected droplets.
- Reduced sunlight exposure may compromise the immune system due to lower vitamin D and melanin production.
- The virus may survive better in colder, drier climates, leading to higher infection rates.
Fluctuating Severity of the Flu
The flu’s ability to mutate and circulate between different species and regions contributes to its variable severity each year. Two main types of changes in the influenza virus are antigenic drift and antigenic shift:
- Antigenic drift involves slow changes in the virus’s outer proteins over time, allowing the immune system to recognize and combat it. However, accumulated drifts can lead to significant changes, making previously acquired immunity less effective and increasing the risk of multiple infections.
- Antigenic shift, a rarer occurrence, results from significant mutations in the virus, usually when an animal flu strain gains the ability to infect humans. These shifts can lead to pandemic events, like the Swine Flu pandemic in 2009.
Flu Vaccine Effectiveness
Due to the flu’s ability to change, the flu vaccine needs periodic updates to target the most prevalent strains effectively. Annually, researchers analyze global flu strains to predict the most dominant ones for the upcoming season. The vaccines typically include the top three to four strains. Though some years see good matches between vaccine and circulating strains, other years may experience reduced vaccine effectiveness if the dominant strains differ from the predictions.
For the 2024 flu season, the FDA recommends vaccines covering two different Influenza A strains and two Influenza B strains. Early data indicates that most flu cases in the United States this year are caused by Influenza A strains, with continued concerns about the H3N2 subtype, which has shown higher hospitalization rates in previous seasons. The updated vaccine should provide protection against these circulating strains.
Protecting Yourself During the 2024 Flu Season
As we approach the flu season, it’s essential to take preventive measures seriously:
- Get vaccinated: The flu vaccine, while not 100% effective, still provides substantial protection against the virus and reduces the severity of illness even if infection occurs.
- Practice preventive habits: Like COVID-19 protocols, maintain a safe distance from sick individuals, wash hands frequently, cover coughs and sneezes, and wear masks in crowded places to reduce the risk of catching and spreading the flu.
- Stay informed: Keep updated with information from credible sources like the CDC and NIH to monitor the flu’s spread and receive essential guidance for protection.
Flu Vaccine Trials at Velocity
If you are interested in participating in flu vaccine trials or other vaccine studies, Velocity Clinical Research is enrolling volunteers. Eligible participants may receive investigational vaccines and, in some cases, an FDA-approved vaccine at no cost, along with possible compensation for study-related time.
For more information on current and upcoming clinical trials at Velocity, visit velocityclinicaltrials.com/find-study.
References and Continued Reading
- Centers for Disease Control and Prevention, Key Facts about Seasonal Influenza.
- Centers for Disease Control and Prevention, Vaccine Effectiveness: How Well Do Flu Vaccines Work?
- Harvard University, Science in the News, The Reason for the Season: why flu strikes in winter.
- Healthline, How Are Influenza A and B Different?
