What You Need to Know About the 2026–2027 Vaccine: 5-Year Trends & Updates

As fall and winter approach, so does the annual influenza season. Because flu viruses continually evolve, global health experts review and update the vaccine composition every year.

Here is a look at how U.S. influenza vaccines have changed over the past five years and what you can expect from the newly updated 2026–2027 Northern Hemisphere flu vaccine.

Early Look at the 2026–2027 Flu Season

Early surveillance data provides an initial snapshot of flu activity heading into the new season. According to CDC FluView data for the week ending September 12, 2026, overall seasonal flu activity remains low [1].

Positivity Rate: Only 1.8% of respiratory specimens tested in U.S. clinical laboratories were positive for influenza [1].

Strain Breakdown: Of those positive specimens, 95.9% were influenza A and 4.1% were influenza B [1].

Subtypes: Among the subtyped influenza A viruses, A(H1N1)pdm09 accounted for 89.8%, while A(H3N2) made up 10.2% [1].

While these early-season figures are useful, they shouldn't be interpreted as a forecast. Flu activity and dominant strains can change substantially as the season progresses.

The Evolution of the Vaccine: From Quadrivalent to Trivalent

One of the most significant changes in U.S. flu vaccination over the past five years has been the shift from quadrivalent (four-strain) to trivalent (three-strain) vaccines [5].

2021–2024 (The Quadrivalent Era): For several years, U.S. flu vaccines were quadrivalent. They were designed to protect against two influenza A viruses (H1N1 and H3N2) and two influenza B lineages (Victoria and Yamagata) [2, 3, 4].

The Disappearance of B/Yamagata: Global surveillance has not detected any B/Yamagata viruses in circulation since March 2020 [5]. Following this prolonged absence, the World Health Organization (WHO) recommended removing it from seasonal vaccines [6]. Note: This decision is based on a lack of detection in surveillance data, not definitive proof that the lineage is permanently eradicated.

2024–2026 (The Shift to Trivalent): Beginning with the 2024–2025 season, the U.S. officially transitioned to trivalent vaccines by dropping the B/Yamagata component [5]. Trivalent vaccines (two A strains and one B strain) remained the standard through the 2025–2026 season, providing equivalent protection against circulating strains without including an inactive component.

Inside the 2026–2027 Flu Vaccine

The WHO issued its recommendations in February 2026, and the FDA finalized the U.S. vaccine composition in March 2026 [6, 7]. The biggest news for the 2026–2027 season is that all three vaccine components have been updated compared to the previous year.

Here are the specific reference viruses selected for this season [7]:

Virus Type	Egg-Based Vaccines	Cell- or Recombinant-Based Vaccines
A(H1N1)pdm09	A/Missouri/11/2025-like virus	A/Missouri/11/2025-like virus
A(H3N2)	A/Darwin/1454/2025-like virus	A/Darwin/1415/2025-like virus
B/Victoria lineage	B/Tokyo/EIS13-175/2025-like virus	B/Pennsylvania/14/2025-like virus

Updating all three components highlights why annual vaccination is essential— the vaccine must adapt to match the viruses that are genetically relevant to the upcoming season.

What This Means for You

For the 2026–2027 season, the CDC continues to recommend annual influenza vaccination for everyone aged 6 months and older, with very limited exceptions [8].

For most people, it is ideal to get vaccinated in the month of September or October [8]. However, getting your shot later in the season still provides valuable protection while flu viruses are actively circulating. Staying up to date with your annual flu vaccine remains the safest and most effective way to protect yourself and your community from severe complications.

References:

1. U.S. Centers for Disease Control and Prevention (CDC). FluView: Weekly U.S. Influenza Surveillance Report (2026, Week 36)

2. CDC Flu Seasons: 2021-2022 Flu Season Summary

3. CDC Flu Seasons: 2022-2023 Flu Season Summary

4. CDC Flu Seasons: 2023-2024 Flu Season Summary

5. CDC/FDA: 2024-2025 Flu Season : Transition to Trivalent Vaccines

6. World Health Organization (WHO): Recommendations for influenza vaccine composition for the 2026-2027 northern hemisphere season. Februray 27, 2026

7. U.S. Food and Drug Administration (FDA). Influenza Vaccine Composition for the 2026-2027 U.S. Influenza Season, March 2026

8. CDC Flu Season: Review information about the 2026-2027 flu season

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