Why the flu season is so bad and how you can protect yourself

Flu Season 2023-2024: Subclade K Variant & Vaccine Effectiveness

Key Concepts:

• Subclade K: A new variant of the influenza virus, specifically within the H3N2 group, currently driving a surge in flu cases.
• H3N2: A subtype of influenza A virus known for its mutability and potential for causing severe illness, particularly in vulnerable populations.
• Vaccine Mismatch: A situation where the influenza strains included in the current vaccine are significantly different from the strains currently circulating, reducing vaccine efficacy.
• Vaccine Efficacy: The measure of how well a vaccine prevents infection, illness, or severe disease.
• Hot Spots (on the virus): Specific areas on the virus that are targeted by the immune system and antibodies. Mutations in these areas can allow the virus to evade immunity.

Flu Activity & Current Situation

As of the week of the interview, the CDC reports high or very high flu activity in 32 U.S. states and jurisdictions, nearly double the number from the previous week. Nationally, over seven million people have been infected this season, resulting in over 3,000 deaths. Vaccination rates remain low, with only approximately 25% of adults and 17% of children having received the flu shot as of November.

The Subclade K Variant – Characteristics & Impact

Andrew Pekosz, a virologist at Johns Hopkins Bloomberg School of Public Health, explains that the current surge is largely driven by the subclade K virus, a variant of H3N2. This variant possesses mutations in “hot spots” – regions on the virus targeted by the immune system – allowing it to evade pre-existing immunity from prior infection or vaccination. This evasion is a primary reason for the increased susceptibility within the population.

Vaccine Effectiveness & the “Mismatch”

This year is characterized by a “mismatch” between the vaccine strain and the circulating virus (subclade K). Mutations in the variant mean that some of the immunity generated by the vaccine doesn’t effectively recognize and neutralize the current virus. This results in a reduction in vaccine efficacy, particularly against infection. However, Pekosz emphasizes that even with a mismatch, the vaccine still offers protection against severe disease. He strongly advises individuals who haven’t been vaccinated to still receive the shot, as it remains beneficial. The influenza vaccine requires approximately two weeks to generate a robust immune response, and flu seasons typically last four to six weeks or longer, meaning there is still time to gain some protection.

Public Health Messaging & Vaccine Controversy

The interview addresses concerns regarding public health messaging, specifically referencing Dr. Mehmet Oz’s statements on TV. Dr. Oz emphasized lifestyle factors for flu prevention (exercise, sunlight, diet, vitamin D, hygiene) while downplaying the vaccine’s effectiveness and labeling it “controversial.” Pekosz strongly refutes this characterization, stating that the influenza vaccine is both safe and effective, though its efficacy varies annually due to the need to predict and manufacture the vaccine months in advance. He explains that the current mismatch is a result of the subclade K variant emerging after the vaccine strain for the Northern Hemisphere was selected in February.

At-Risk Populations & Severity of Illness

While anyone can contract the flu, certain populations are at higher risk of severe illness. These include young children (under 11) and individuals over the age of 65. Currently, data indicates a proportionate rise in severe cases alongside the increase in overall cases, suggesting that subclade K is not inherently more dangerous than other H3N2 viruses, but its increased transmissibility leads to more infections and, consequently, more severe cases.

Geographic Variations in Outbreaks

Flu activity varies geographically, with some states experiencing outbreaks earlier than others. New York was identified as one of the first states significantly impacted by subclade K. The spread of the virus is often described as a matter of “bad luck” – where the virus initially lands and begins to spread. The expectation is that other states will experience similar surges in cases over the coming weeks.

Notable Quotes:

• Andrew Pekosz: “This clade K virus has changed from the viruses that circulated last year. And, importantly, it also has changed based on the vaccine that was distributed earlier this fall and is still available.”
• Andrew Pekosz: “There's nothing really controversial about the influenza vaccine. We know that it works. We know that it's safe.”
• Andrew Pekosz: “It’s just that more people are susceptible. And, therefore, we will be seeing more cases and a corresponding or proportionate rise in the number of severe cases.”

Conclusion

The current flu season is being significantly impacted by the emergence of the subclade K variant, leading to increased illness and hospitalizations. While the vaccine’s effectiveness is reduced due to a mismatch between the vaccine strain and the circulating virus, vaccination remains a crucial preventative measure, particularly against severe disease. Public health officials emphasize the importance of accurate messaging regarding vaccine efficacy and the continued need for vaccination, even during a season with a circulating variant. Vulnerable populations – young children and the elderly – remain at the highest risk for severe illness. The spread of the virus is expected to continue across the country in the coming weeks.