Every year, the flu vaccine has to be remade.

Health authorities study which flu strains are spreading, predict which ones will dominate the coming season, and vaccine makers produce a new version months in advance. When the prediction is off, the vaccine works less well.

Scientists have long wanted to break that cycle with a universal flu vaccine: one that protects against many different flu viruses at once, without constant updates.

Researchers at the US National Institutes of Health have now reported the first human trial of one such candidate, called BPL-1357.

The early results: it was well tolerated and produced antibody responses against several different types of flu virus.

Flu keeps changing, so the vaccine must too

Influenza viruses mutate quickly. Small changes in the proteins on their surface, the ones our immune system learns to recognize, add up from season to season.

That means antibodies made against last year’s virus may not recognize this year’s version well. It’s why seasonal vaccines are updated and why people are advised to get vaccinated every year.

Occasionally, flu viruses also jump from animals such as birds into people, bringing entirely new surface proteins that few humans have immunity to. Those are the viruses that can cause pandemics.

BPL-1357 is built from four whole bird flu viruses

Most seasonal flu vaccines target the strains expected to circulate in humans that year.

BPL-1357 takes a different approach. It contains four whole bird flu viruses, chosen to cover a range of flu “subtypes,” the families defined by the virus’s main surface proteins. The viruses are inactivated, meaning they’ve been chemically killed and can’t cause infection.

The idea is that exposing the immune system to a broad mix of flu proteins could train it to recognize many flu viruses, including ones it hasn’t seen.

In earlier animal studies, the researchers report, the vaccine gave strong protection.

45 adults took part in the first human trial

This was a phase 1 trial, the first stage of human testing, designed mainly to check safety.

  • 45 healthy adults took part.
  • They were randomly assigned to receive the vaccine as an injection into the arm, as a nasal spray, or a placebo.
  • Each got two doses, 28 days apart.
  • Neither participants nor researchers knew who got what.

It was well tolerated and triggered broad antibody responses

Safety: Side effects were mostly mild and affected a minority of participants. Sore arms were more common in the injection group.

Immune response: The injected vaccine produced antibody responses against three different flu subtypes:

  • H3, a type that circulates in humans every flu season: 71% of recipients
  • H5, the bird flu subtype that includes the H5N1 virus that has spread among birds and some mammals: 71%
  • H7, another bird flu subtype: 86%

Injected participants also produced antibodies able to neutralize the virus in lab tests.

The nasal spray, however, produced only weak responses. And while the researchers hoped the vaccine would generate antibodies in the lining of the nose, where flu first enters the body, the injected version did not.

Antibodies aren’t the same as protection

It’s important to be clear about what this trial shows.

Producing antibodies is a sign that the immune system noticed the vaccine. But it doesn’t prove those antibodies would stop someone from catching the flu or getting seriously ill.

That question requires larger trials in which vaccinated people are exposed to flu, either naturally or in carefully controlled studies.

The researchers themselves say they still need to test other doses, characterize the immune response further and evaluate whether the vaccine actually prevents infection and disease.

What the study doesn’t show

This is a peer-reviewed study, but a very small, early-stage trial. With 45 people split across three groups, the response percentages come from small numbers of participants.

It did not test protection against flu, and it did not show that seasonal vaccine updates could be eliminated.

One of the researchers is an inventor on the NIH’s patent for the vaccine, which the paper discloses.

Most importantly, the results don’t change current advice. Seasonal flu vaccination remains the recommended way to reduce the risk of flu.

A universal flu vaccine has taken its first step

A vaccine that works against many flu viruses could reduce the guesswork of seasonal vaccine design and help prepare for the next flu pandemic.

BPL-1357 has cleared the first hurdle: in a small group of people, it was safe and triggered broad immune responses.

The harder tests are still ahead.

A flu vaccine that doesn’t need yearly updates is still a goal, but this one has taken its first step.