Flu Season 2024-2025: Comprehensive Guide for Healthcare Professionals
From trivalent shifts to global surveillance: earn free CME credits while you polish up your flu vaccine knowledge!
As we approach the 2024-2025 respiratory virus season, it's important to refresh our knowledge about the flu and flu vaccines…
With that, we are extremely excited to announce that we have partnered with Integrity CE to develop four FREE CME modules for HCPs thanks to an educational grant from CSL Seqirus!
Here are the four courses:
1. Overview of the Flu and the Flu Vaccine
2. Safety and Effectiveness of Flu Vaccines
3. Special Populations and Considerations for Flu Vaccination
4. Commonly Asked Questions (and Answers!) About Flu Vaccines
Each of these courses offers an AMA PRA Category 1 CreditTM. To earn credit:
Click the course links below to access the Integrity CE website.
Create a free account if you don't already have one.
Complete the pretest.
View the course content.
Take the posttest and complete the evaluation.
Once you've finished these steps, you can claim your credit.
But in the meantime, let’s do a lil recap!
Transmission Routes of Respiratory Viruses
Respiratory viruses spread through several mechanisms:
Droplet Transmission: Large virus-containing particles expelled through coughing, sneezing, or talking. These droplets typically travel short distances before falling.
Aerosol Transmission: Smaller particles that can remain airborne for extended periods and travel further distances.
Fomite Transmission: Virus particles on contaminated surfaces, though less common for respiratory viruses.
Direct Contact: Physical contact with an infected person, such as handshakes or hugs.
So, TL;DR: In addition to vaccination– masking, hand washing, ventilation, and all the usual respiratory virus mitigation measures are important when it comes to dodging the virus.
Viral Evolution: A Moving Target!
Viruses are constantly evolving, presenting ongoing challenges for our immune systems and vaccination efforts since developing vaccines that match circulating strains is like trying to hit a moving target:
Antigenic Drift: Gradual, small changes in virus genes due to mutations. These incremental changes contribute to the need for annual flu vaccinations. Minor genetic mutations in influenza viruses accumulate over time, resulting in viruses that are typically closely related and cluster near each other on a phylogenetic tree. These closely related viruses often share similar antigenic properties, meaning that antibodies produced by your immune system in response to one strain can also recognize and fight off other antigenically similar strains—a phenomenon known as “cross-protection.”
Antigenic Shift: Abrupt, major changes, typically when different strains combine or jump species. These significant alterations can lead to pandemics.
Case Study: The 2009 H1N1 Pandemic
The 2009 H1N1 pandemic is an example of antigenic shift. A new influenza A virus emerged, combining genes from human, swine, and avian flu viruses. This created a strain to which most people had little to no immunity, leading to its rapid global spread. In other words…bad news bears. The existing annual flu vaccine was not effective against the newly emerged strain. As a result, a separate H1N1-specific vaccine had to be developed and distributed to provide immunity against this novel strain.
Global Surveillance: Leveraging Southern Hemisphere Data for Northern Hemisphere Predictions
The asynchronous nature of influenza seasons between hemispheres provides a unique opportunity for predictive epidemiology. Southern Hemisphere surveillance data serve as a critical leading indicator for Northern Hemisphere preparedness (kinda like our very own flu crystal ball), offering insights into viral evolution, strain dominance, and potential vaccine efficacy.
Key aspects of this hemispheric data transfer include:
Antigenic Drift Analysis: Monitoring genetic and antigenic changes in circulating strains allows for early detection of viral mutations that may impact vaccine effectiveness.
Transmission Dynamics: Patterns of viral spread and population susceptibility in the Southern Hemisphere can inform mathematical models predicting Northern Hemisphere epidemic trajectories.
Vaccine Composition Refinement: Southern Hemisphere data directly influences WHO recommendations for Northern Hemisphere vaccine formulations, allowing for last-minute adjustments to address emerging strains.
Cross-Protection Assessment: Evaluation of vaccine-induced immunity against circulating Southern Hemisphere strains provides valuable data on potential cross-protective effects for the Northern season.
Antiviral Resistance Surveillance: Early detection of antiviral-resistant strains enables proactive adjustments to treatment protocols and public health strategies.
This year's Southern Hemisphere observations, including H3N2 predominance in South America, H1N1 prevalence in parts of Africa, and a mixed strain profile in Australia, offer a complex picture that underscores the importance of comprehensive global surveillance in shaping evidence-based preparedness strategies for the impending Northern Hemisphere influenza season.
Implications for the 2024-2025 Flu Season
This foundational knowledge of viral transmission and evolution directly impacts our approach to the upcoming flu season. It informs everything from vaccine formulation to public health strategies and individual patient recommendations.
Flu Vaccine Technologies:
Modern flu vaccines employ three main production methods, each with unique advantages:
Egg-Based Vaccines
Traditional method using fertilized chicken eggs to grow the virus
Examples: Fluzone, FluMist
An EGGS-ellent Update: As of the 2023-2024 season, the CDC recommends that people with egg allergies, including those with severe allergies, can receive any licensed, recommended, age-appropriate influenza vaccine. This is a significant change from previous guidance and removes a barrier to vaccination for many individuals.
Cell-Based Vaccines
Uses cultured animal cells (typically canine kidney cells) to grow the virus
Offers faster production and potentially better matching to circulating strains
Example: Flucelvax
Egg-free
Recombinant Vaccines
Utilizes recombinant DNA technology
Egg-free and live virus-free production
Allows for rapid manufacturing, crucial during pandemics
Example: Flublok
Types of Flu Vaccines: Addressing Diverse Needs
Flu vaccines come in two main types: inactivated influenza vaccines (IIV) and live attenuated influenza vaccines (LAIV).
IIV is the most common type, administered as an injection. It contains killed virus and is approved for people 6 months and older, including pregnant individuals and those with certain chronic health conditions.
LAIV, marketed as FluMist, is a nasal spray containing weakened live viruses. It offers an alternative for individuals aged 2-49 who have needle phobia. However, LAIV has specific guidelines:
Not recommended for pregnant individuals
Not suitable for people with weakened immune systems
Should not be given to people with certain medical conditions
While LAIV provides a needle-free option, it's crucial to consult with a healthcare provider to determine eligibility, as the criteria for its use are more restrictive than for IIV.
2024-2025 Season: The Shift to Trivalent Vaccines
This season marks a significant change in vaccine composition. We're moving from quadrivalent to trivalent vaccines, which will protect against:
One influenza A(H1N1) virus
One influenza A(H3N2) virus
One influenza B/Victoria lineage virus
The B/Yamagata lineage has been removed due to its absence in circulation since March 2020. This adjustment streamlines production without compromising protection against currently circulating strains.
Demystifying Vaccine Ingredients
Understanding vaccine components is crucial for addressing patient concerns and ensuring informed consent. Key ingredients include:
Preservative used in multi-dose vials
Contains ethylmercury, which is fundamentally different from methylmercury
Ethylmercury is eliminated from the body much more quickly than methylmercury (half-life of about 7 days vs. 50 days)
The amount in vaccines is far below any level of concern
Not present in single-dose vials or prefilled syringes
Used to inactivate viruses during production
Present in extremely small, safe quantities
The human body naturally produces and metabolizes formaldehyde daily
A typical 2-month-old baby has around 1.1 mg of formaldehyde in their body, while a single dose of vaccine contains about 0.1 mg
Breast milk contains 50-70 times more formaldehyde than vaccines
Adjuvants (e.g., aluminum salts)
Enhance immune response
Help boost antibody production
Stabilizers (e.g., sugars, gelatin)
Maintain vaccine effectiveness during storage and transport
Recommendations for Adults 65 and Older
For older adults, the CDC recommends one of the following higher-dose or adjuvanted flu vaccines:
a) Fluzone High-Dose vaccine b) Flublok recombinant flu vaccine c) Fluad adjuvanted vaccine
These vaccines have shown superior efficacy in this age group, with studies demonstrating up to 24.2% greater effectiveness in preventing laboratory-confirmed influenza compared to standard-dose vaccines.
Addressing Common Concerns with Empathy and Science
For our HCPs in the house, here are some answers to questions you may receive from your patients:
"Why do I need a flu shot every year?" Response: "The flu virus changes a little each year (antigenic drift), and our immunity can wane over time. Annual vaccination ensures the best protection against the most likely flu strains each season."
"Can the flu vaccine give me the flu?" Response: "The flu vaccine cannot cause the flu. It contains either inactivated virus or just parts of the virus, neither of which can cause infection. You might experience mild side effects as your body builds immunity."
"I'm pregnant. Is the flu vaccine safe for me and my baby?" Response: "Yes, it's safe and highly recommended during pregnancy. In fact, pregnant individuals who receive the flu vaccine not only reduce their own risk of severe illness but also pass protective antibodies to their newborns."
"I have an egg allergy. Can I still get vaccinated?" Response: "Yes, you can. As of the 2023-2024 season, the CDC recommends that people with egg allergies (even severe ones) can receive any age-appropriate flu vaccine."
"I'm afraid of needles. Are there other options?" Response: "Yes, there's a nasal spray flu vaccine (LAIV) for those who meet specific criteria. It's approved for healthy, non-pregnant individuals aged 2-49 years. However, it's not recommended for certain groups, including those with weakened immune systems or certain medical conditions."
Vaccine Effectiveness: Managing Expectations
While efficacy varies annually, flu vaccines generally reduce the risk of illness by 40-60%. Even in years with lower efficacy, vaccination remains crucial, as it significantly reduces the risk of severe illness, hospitalizations, and complications. For the 2023-2024 season, preliminary data showed:
41–44% effectiveness in preventing flu-related hospitalizations for adults
52–61% effectiveness for children
33–49% effectiveness in reducing outpatient visits for adults aged 18 and older
Special Populations and Considerations
Immunocompromised Patients: While these individuals may have a reduced immune response, annual flu shots are still recommended. In some cases, a second dose or a high-dose/adjuvanted vaccine might be considered.
Coadministration with COVID-19 Vaccines: Flu vaccines can be safely administered simultaneously with COVID-19 vaccines, as supported by recent studies.
Pregnancy and Breastfeeding: Vaccination is strongly recommended at any trimester and while breastfeeding.
Additional Prevention Strategies
Masking: Some individuals, particularly those at high risk for severe flu complications, may choose to wear masks during flu season. Healthcare professionals should strongly consider masking, especially when in close contact with patients, to protect both themselves and those they care for.
Addressing Fear and Misinformation: Building Trust in Science
Despite the overwhelming evidence supporting vaccine safety and efficacy, fear of vaccine ingredients and distrust of science persist, fueled by misinformation. Here's how providers can address these concerns:
Fear of Ingredients: Explain that ingredients like mercury or formaldehyde are either present in very small amounts or are eliminated during production, posing no harm to the body. Emphasize that our bodies naturally produce and process these substances in much larger quantities than found in vaccines.
Distrust of Science: Acknowledge past concerns while emphasizing the rigorous processes vaccines undergo before approval. Transparency about testing, safety data, and ongoing monitoring is crucial in rebuilding trust.
Tailored Communication: Ask open-ended questions to understand specific fears and provide personalized, empathetic responses.
Overcoming Barriers to Vaccination
Cost: Flu vaccines are generally covered by insurance under the ACA. For those without insurance, public health programs offer free or low-cost options.
Access: Offering flexible hours, mobile clinics, or workplace vaccination events can help improve access.
Misinformation: Combat misinformation with empathy, clear explanations, and credible sources like professional medical organizations and public health agencies.
New Developments: Universal and Combination Vaccines
Ongoing research is focusing on creating a universal flu vaccine that could potentially eliminate the need for annual vaccination. Another area of innovation is combination vaccines, such as a flu and COVID-19 vaccine, which could simplify immunization schedules and likely improve uptake. In fact, in a large trial, a combo flu+COVID mRNA vaccine showed better protection against both SARS-CoV-2 and influenza compared to individual vaccines. This could simplify vaccination schedules and improve uptake, offering a more comprehensive immunization strategy for respiratory viruses.
Conclusion
Vaccination remains a cornerstone in preventing influenza and its complications. By staying informed, addressing concerns with empathy and science, and implementing comprehensive prevention strategies, we can collectively work towards better community health during the flu season.
Wishing everyone a healthy flu season,
Unbiased Science