H3N2 Influenza: Breaking Down the Anatomy of a Seasonal Virus

Annual flu vaccines are formulated to include two influenza A strains representing H1N1 and H3N2 subtypes, along with two influenza B strains from the Victoria and Yamagata lineages. These strains co-circulate in the human population, with H3N2-associated strains often linked to severe flu seasons. In three out of the last five severe flu seasons, H3N2 strains dominated.

The 2016/2017 flu season saw a decline in the protective efficacy (approximately 28-42%) of the H3N2 component in the influenza vaccine against co-circulating strains. Since their introduction in 1968, H3N2 influenza viruses have undergone rapid genetic and antigenic evolution to evade host immune responses.

This evolution includes adding N-linked glycans to the viral hemagglutinin (HA), altering the overall net charge of the HA molecule, changing receptor binding preferences, and modifying neuraminidase (NA) functions.

These ongoing adaptations pose challenges in characterizing modern H3N2 influenza viruses. This article discusses the influenza H3N2 virus symptoms and vaccines!

Recognizing H3N2 Influenza Symptoms

Could it be the notorious H3N2 influenza virus? Let's explore H3N2 influenza virus symptoms to decode what your body might be signaling.

1. The Rise of Body Temperature: One of the telltale signs of H3N2 influenza is the abrupt onset of fever. Your body temperature spikes, leaving you feeling achy, fatigued, and just a bit under the weather. It's your body's way of signaling that something's amiss.
2. Cough Chronicles: H3N2 brings along its sidekick—a persistent cough. This isn't your ordinary throat tickle; it's a relentless cough that lingers, disrupting your peace and quiet. The viral intrusion often targets the respiratory system, triggering this incessant urge to cough.
3. Sneaky Sniffles: Nasal congestion and runny noses join the party, making your daily routine a tad more challenging. The H3N2 influenza virus has a knack for affecting your respiratory passages, leading to that classic stuffy nose and a symphony of sniffles.
4. Body Aches and Pain: Ever felt like your body took a beating after a day of flu? H3N2 influenza can orchestrate a symphony of body aches and pains, leaving you feeling sore and worn out. It's a distinctive feature that often accompanies the viral invasion.
5. Headaches and Fatigue: As if the fever, cough, congestion, and body aches weren't enough, H3N2 throws in headaches and fatigue for good measure. Your energy levels plummet, and your head might throb with discomfort, adding to the overall unwell feeling.

Story of the Influenza H3N2 Vaccine

The dynamics of influenza viruses constantly challenge our defenses, and the recent seasons have unveiled unique insights, particularly regarding the H3N2 subtype. Let's explore the effectiveness of the influenza H3N2 vaccine during the 2021–2022 season and understand its impact on different age groups.

The COVID-19 pandemic brought about an unprecedented low in influenza circulation during the 2020–2021 season. However, the subsequent season witnessed a resurgence in influenza cases, accompanied by distinct challenges posed by the 2a.2 subgroup of the influenza A (H3N2) 3C.2a1b subclade.

1. Assessing Vaccine Effectiveness: To gauge the effectiveness of the 2021–2022 influenza H3N2 vaccine, a robust surveillance network monitored hospitalized cases of acute respiratory illness among adults aged 18 years and above. By employing a test-negative design, the study evaluated vaccine effectiveness by comparing influenza-positive case-patients with controls, considering factors like age and immunocompromising conditions.
   
   
2. Vaccine Effectiveness in Different Age Groups: The study's findings shed light on the varied impact of the influenza H3N2 vaccine across different age brackets. Among adults aged 18–64 years, the vaccine demonstrated a 26% effectiveness, providing a crucial shield for younger, immunocompetent individuals.
   
   However, the effectiveness plummeted to -3% among adults aged 65 years and above, underscoring challenges in safeguarding this older demographic.
   
   Currently, when COVID-19 has taken over our world, it is crucial not to overlook other viruses like H3N2 influenza. The good news is that Pathkind Labs offers a comprehensive COVID-19 H3N2 Combi Panel that includes two important tests. This panel not only detects the presence of viruses but also provides detailed clinical history that can aid in accurate diagnosis and treatment.
   
   
3. Lessons from Inclusion of SARS-CoV-2–Positive Controls: A separate analysis was conducted to explore the influence of including SARS-CoV-2–positive controls in the study. This illuminated potential biases and complexities introduced when dealing with dual respiratory infections, highlighting the need for nuanced strategies in such scenarios.
   
   In a season where the influenza A(H3N2) virus deviated antigenically from the vaccine strain, the vaccine's impact was evident in reducing the risk of influenza hospitalization, particularly in younger adults. However, gaps in protection for the elderly point towards the ongoing necessity for improvements in vaccine formulations, antiviral strategies, and preventive measures.

Conclusion

H3N2 influenza virus may seem like a constantly evolving and complex threat, but with the right knowledge and tools, we can better understand and combat it. By breaking down the anatomy of this seasonal virus, we have learned about its origins, mutations, and potential risks.

With current advancements in technology, such as the H3N2 Real-Time PCR test by Pathkind Labs, we now have the ability to quickly and accurately identify the presence of this virus in our bodies.

But this knowledge is not enough on its own. It is crucial that individuals take preventive measures to protect themselves from infection. This includes practicing good hygiene habits such as washing hands regularly, getting vaccinated against influenza strains (including H3N2), and staying home when sick to prevent the spread of illness.