Trivalent vs quadrivalent flu vaccine: what's the difference, and is the extra worth paying for?
How 3-strain and 4-strain flu vaccines compare, which viruses each covers, why the WHO changed its recommendation, and which to choose this year.
When you come for a flu shot you're often asked: 3 strains or 4? The price difference is small, but the answer to 'is it worth it?' has changed in the last few years, because one flu strain has effectively disappeared from the world since 2020. Below is what 3 and 4 mean and how to decide on today's evidence.
Key takeaways
- Both cover the same two influenza A strains (H1N1 and H3N2) and the B/Victoria lineage.
- The quadrivalent adds B/Yamagata, which has not been confirmed anywhere in the world since March 2020.
- The WHO has allowed a return to trivalent formulations from the 2024–2025 season, and many countries are switching.
- At Mongkhondee Clinic the trivalent is 440 baht/dose and the quadrivalent 490 baht/dose. Either is fine; getting one every year matters more.
What the 3 and 4 mean
Two main types of influenza virus circulate in people: A and B. The common A strains are H1N1 and H3N2; type B splits into two lineages, Victoria and Yamagata. A trivalent vaccine contains two A strains and one B lineage; a quadrivalent contains both B lineages.
In the past the quadrivalent had a clear advantage, because it was hard to predict which B lineage would circulate each year, and a wrong guess left the trivalent covering B less well. That made the quadrivalent the global standard from about 2012 to 2022.
What changed after 2020
Lockdowns during the COVID-19 pandemic pushed influenza B/Yamagata out of surveillance systems, and there has been no confirmed detection since March 2020. From 2023 the WHO stated that the B/Yamagata component is no longer needed and recommended that manufacturers may return to a trivalent formulation.
The United States switched all vaccines to trivalent from the 2024–2025 season. In Thailand both types are still sold side by side, because manufacturers are adjusting their production lines at different speeds.
The two vaccines compared
| Trivalent (3) | Quadrivalent (4) | |
|---|---|---|
| A/H1N1 | Yes | Yes |
| A/H3N2 | Yes | Yes |
| B/Victoria | Yes | Yes |
| B/Yamagata | No | Yes (not seen circulating since 2020) |
| Minimum age | Per each brand's label, mostly 6 months+ | 6 months+ |
| Doses | 1 a year | 1 a year |
| Price at the clinic | 440 baht/dose | 490 baht/dose |
So which should you choose?
On current evidence the difference in protection is almost nil, because the strain that differs is one that no longer circulates. The quadrivalent isn't worse, but its extra component may go unused, and new trivalent vaccines are made to the WHO's latest formulation too.
What affects protection far more is getting vaccinated every year, before the flu season, with a vaccine suited to your age and health. See when to get your flu shot, and for young children, how many doses children aged 6 months to 8 years need.
The clinic stocks both the trivalent and quadrivalent vaccines, plus the nasal spray for anyone who'd rather avoid a needle. Message us on LINE to check stock before travelling.
Good to know: Brands and types in stock change with imports and the season. Prices are the clinic's published prices and may be revised.
Are the side effects different?
No significant difference. Both are inactivated vaccines. Expected effects are soreness, swelling or redness at the injection site, aches, a low fever or tiredness for 1–2 days. An injected vaccine cannot give you flu. For who should take extra care, see who should get the flu vaccine.
Frequently asked questions
Yes. Each year's vaccine is made to the WHO's new formulation; you don't need the same type every year.
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Sources
- Recommended composition of influenza virus vaccines for use in the 2025–2026 northern hemisphere influenza season World Health Organization
- Trivalent Influenza Vaccines U.S. Centers for Disease Control and Prevention
This content is general information and does not replace an examination, diagnosis or personal advice from a doctor. Published 20 September 2026
Everyone's health is different
If you have a health condition, take regular medication, are pregnant or have unusual symptoms, let a doctor assess you first. Message us on LINE.
