The 2026/27 influenza vaccination season has been hit by significant supply problems, with Sanofi’s recombinant influenza vaccine Supemtek particularly affected. Practices and pharmacies have reported reduced or cancelled orders all over facebook and other forums, and UKHSA has now acknowledged that manufacturing Northern Hemisphere influenza vaccines for the 2026/27 season has been “very challenging”

Eek. It feels like a rocky start to flu season...

So, let's look at why we are where we are because I personally feel that the more you know about a situation, the less annoying and uncertain it seems to become. Plus, I'm a very nosey vaccine geek and I like to know what's going on behind the scenes.

There are really two separate issues: a difficult manufacturing season affecting several suppliers, and an additional Sanofi-specific problem affecting Supemtek.

Firstly:

For 2026/27, all three influenza vaccine antigen components changed compared with the previous season:

• A/Missouri/11/2025 (H1N1)pdm09-like

• A/Darwin/1415/2025 (H3N2)-like

• B/Pennsylvania/14/2025 (B/Victoria lineage)-like

That is unusual and increases manufacturing pressure because manufacturers have only a short window between WHO strain selection in February and delivery before the autumn programme. The WHO certainly likes a tight deadline.

It also seems that there was also delayed identification and availability of material relating to the influenza B component, which further compressed production timelines.

But, this doesn't fully explain Supemtek...

Supemtek is a recombinant influenza vaccine, IIVr.

Unlike conventional egg-based or cell-based vaccines, recombinant vaccines do not need influenza virus itself to be grown. The haemagglutinin gene is inserted into a baculovirus expression system and the antigen is produced in insect cells. It's really clever stuff including insect technology and quite fascinating if you like that kind of thing.

WHO specifically notes that recombinant protein influenza vaccines do not require candidate vaccine viruses in the same way as conventional vaccines.

So the late B strain issue is part of the wider manufacturing backdrop, but it does not fully explain the loss of Supemtek supply.

Sanofi has confirmed that it experienced a separate “manufacturing challenge” affecting Supemtek. Professional bodies have described a batch loss of sorts, e.g. Londonwide LMC reported that cancellations were occurring because of a “batch failure”.

The Dispensing Doctors’ Association and trade publications have reported that around two million doses may have been affected, although Sanofi has not publicly confirmed that exact figure.

Some practices and pharmacies have had orders substantially reduced, while others have been told their Supemtek order will not be delivered at all.

Why did the batch fail?

Nobody knows.

Well Sanofi do, but they have not publicly disclosed the precise technical cause.

A vaccine batch can fail for many reasons, including problems with antigen yield, potency, purification, formulation, filling, stability, sterility or another predefined quality specification. It could really be ANYTHING!

But there is currently no reliable evidence showing which of these applied to Supemtek.

It is therefore important not to let patients think that the vaccine was contaminated or unsafe. You know how people's minds like to wander on hearing news like this. A manufacturing batch failure means the product did not progress through manufacture or quality release; it does not mean defective vaccine reached patients. Sanofi are great. They are super thorough, and this just means their processes had some integrity about it.

BUT, is Sanofi the only manufacturer affected?

No.

Viatris will not supply influenza vaccine to the UK for the 2026/27 season following production problems too.

Seqirus has also experienced a separate filling-line issue, causing some cell-based vaccine deliveries to be rephased, although reports indicate that this backlog is being cleared.

Sanofi’s Efluelda high-dose vaccine has not been reported as being affected by the same Supemtek batch failure.

But on to the most important part. What does this mean in clinics?

UKHSA has warned that some inactivated flu vaccines may be unavailable, limited in quantity or delivered later than expected. Clinics should therefore review their vaccine mix now rather than assuming original orders will arrive as planned.

• For adults under 50 years, IIVc and IIVr are the preferred injectable vaccines.

• Older adults have more options, including enhanced vaccines such as adjuvanted influenza vaccine and high-dose influenza vaccine.

This means scarce IIVc stock should not automatically be used in older adults if an appropriate age-specific vaccine is available.

A practical example is a 28-year-old pregnant woman. Her appropriate injectable options are more limited than those of a 70-year-old who may be able to receive an adjuvanted or high-dose vaccine. If IIVc is used unnecessarily in older adults, clinics may later find they have insufficient stock for younger eligible patients like that lady who do not have the same alternatives.

In practical terms, clinics should:

1. check whether any Supemtek orders have been reduced or cancelled;

2. review which vaccines are actually arriving and when;

3. use age-specific enhanced vaccines for older adults where appropriate;

4. preserve IIVc and IIVr stock for younger eligible patients where possible;

5. avoid delaying vaccination simply to wait for one particular brand;

6. use another appropriate JCVI-recommended vaccine where the intended product is unavailable.

NHS England and pharmacy organisations have indicated that alternative Seqirus stock should be available to support providers affected by Sanofi cancellations.

The key message

The wider 2026/27 flu vaccine market is under pressure because all three vaccine strains changed and the manufacturing timetable was unusually difficult. On top of that, Sanofi experienced a separate manufacturing failure affecting Supemtek, leading to a substantial loss of supply and cancelled or reduced UK orders. For clinics, however, the practical message is clear: review stock plans early, use age-specific vaccines intelligently and protect limited IIVc/IIVr supply for patients who have fewer suitable alternatives.

Best of luck everyone, you're awesome!!