🦠 Types of Influenza & 💉 Types of Flu Vaccines

Joseph Peng
Mar 1
3 min read

Influenza (flu) is an acute respiratory infectious disease caused by the influenza virus. It is highly contagious, rapidly mutating, and seasonal. Every year, millions of people worldwide contract the flu, with elderly individuals, children, and people with chronic illnesses being the most vulnerable to severe cases.

So, what are the types of influenza? How do different vaccines work? Let’s find out!

🦠 Types of Influenza (by Virus Type)

Influenza viruses are classified into A, B, C, and D types, with A and B being the most responsible for seasonal flu outbreaks.

1️⃣ Type A Influenza (H1N1, H3N2)

✅ Highly variable, spreads widely, and causes the most severe cases✅ Can be transmitted between humans and animals (e.g., bird flu, swine flu)✅ Responsible for global flu pandemics (e.g., the 2009 H1N1 pandemic)

Common Strains:

H1N1 (Caused the 2009 global pandemic, also known as "swine flu")
H3N2 (A frequent cause of seasonal flu, more severe in the elderly)
H5N1, H7N9 (Bird flu strains, occasionally infect humans with high fatality rates)

2️⃣ Type B Influenza

✅ Only spreads among humans, does not cause pandemics but still leads to seasonal outbreaks✅ Symptoms are usually milder than Type A but can still cause complications✅ Divided into two lineages:

Victoria lineage (Common in seasonal flu outbreaks)
Yamagata lineage (Less frequently observed in recent years)

3️⃣ Type C Influenza

✅ Causes mild symptoms similar to the common cold✅ Mainly affects children, rarely leads to severe illness

4️⃣ Type D Influenza

✅ Primarily infects cattle and pigs, not known to infect humans yet

💉 Types of Flu Vaccines

Since influenza viruses mutate frequently, flu vaccines need to be updated and administered annually. Flu vaccines can be categorized based on their composition and method of administration.

🔹 1. By Composition

✅ Trivalent Flu Vaccine (TIV)

Contains two Type A strains + one Type B strain
Less commonly used today due to its limited coverage

✅ Quadrivalent Flu Vaccine (QIV) (Most Recommended)

Contains two Type A strains (H1N1, H3N2) + two Type B strains (Victoria, Yamagata)
Provides broader protection against circulating flu viruses

🔹 2. By Production Method

✅ Inactivated Flu Vaccine (IIV) 💉 (Most Common)

Contains inactivated (killed) flu viruses
Recommended for people aged 6 months and older, including elderly and pregnant women
Safe and effective, does not cause infection

✅ Recombinant Flu Vaccine (RIV) 🧬 (Egg-Free Option)

Produced using genetic engineering, does not require egg-based cultivation
Recommended for people aged 18+ who have severe egg allergies
Advantage: Avoids egg-related allergic reactions

✅ Adjuvanted Flu Vaccine (aIIV) 🔥 (For Older Adults)

Contains an adjuvant to enhance immune response
Recommended for people aged 65+
Provides stronger and longer-lasting immunity

✅ High-Dose Flu Vaccine (HD-IIV) 💪 (For Older Adults)

Contains four times the antigen content of standard vaccines
Recommended for people aged 65+
Boosts immune response and reduces hospitalization risk

✅ Live Attenuated Nasal Spray Vaccine (LAIV) 🌬 (For Children & Young Adults)

Contains weakened live flu virus, administered via nasal spray
Recommended for healthy individuals aged 2-49
Not suitable for elderly, pregnant women, or immunocompromised individuals
Advantage: No needles, painless administration

🧐 Which Vaccine is Right for You?

Target Group	Recommended Vaccine
Healthy individuals (6 months-64 years)	Quadrivalent inactivated vaccine (QIV)
Adults 65+	High-dose (HD-IIV) or adjuvanted vaccine (aIIV)
Pregnant women	Quadrivalent inactivated vaccine (QIV), NO nasal spray!
Children (2-17 years)	Quadrivalent inactivated vaccine or nasal spray (LAIV)
People with egg allergies	Recombinant flu vaccine (RIV)

📢 Since flu viruses evolve constantly, getting vaccinated annually is essential for effective protection!

📢 Summary

✅ Type A influenza is the most common and severe, while Type B also causes seasonal outbreaks.✅ The quadrivalent flu vaccine (QIV) is the most recommended for broad protection.✅ Older adults, children, pregnant women, and people with chronic diseases are at higher risk and should prioritize vaccination.✅ Flu vaccines must be updated yearly to match the latest circulating strains!

💉 Influenza can be prevented—vaccination + healthy habits = best protection! 💪😷