Parkinson's vaccine: ACI-7104 passes its first test

A vaccine against Parkinson's sounds like science fiction. I have looked at the latest data from the Swiss company AC Immune, and they are interesting, even if they need to be put into proper context.

What is it about?

In Parkinson's, the protein alpha-synuclein clumps together in nerve cells. These clumps are considered one of the drivers of the disease, and they seem to spread from cell to cell. The idea behind active vaccination: the body itself should produce antibodies against these harmful clumps, just as with a classic vaccination. Unlike antibody infusions such as prasinezumab, you would not have to go on a drip every four weeks, only get an occasional booster.

ACI-7104 is a further developed version of the vaccine PD01A, which originally came from the Vienna company Affiris. AC Immune took it over in 2021.

The trial

• Phase 2 (VacSYn, NCT06015841), Part 1
• 34 people with early Parkinson's: 25 received the vaccine, 9 a placebo
• The sole aim of Part 1 was to test whether the vaccine is safe and whether the body produces antibodies
• The results after 100 weeks were published at the end of September 2026

The results

• All main goals were met.
• All vaccinated participants produced antibodies against alpha-synuclein after three vaccinations. These bind preferentially to the clumped, harmful form.
• The antibodies were detectable in the spinal fluid of all vaccinated participants, that is, where they are supposed to work.
• The vaccine was well tolerated. The most common reactions were at the injection site, along with fatigue, headaches and colds.
• In an interim analysis from December 2025, the nerve damage marker neurofilament light chain remained stable in the vaccinated group, while it rose with placebo. There were also first signs that the vaccine reaches its target in the brain.

My assessment

This is an important step, but not yet proof that the vaccine slows Parkinson's. Part 1 was not designed to show a clinical effect at all. With 34 participants the group is very small, and the biomarker signals are preliminary. That the body produces antibodies and that they reach the brain is the prerequisite, nothing more.

The experience with antibody infusions against alpha-synuclein also calls for caution: prasinezumab missed its main goal in the large PADOVA trial, even though there were signs of a slower course. Whether the approach works in principle therefore remains open.

Still, I find the direction exciting. A vaccine that stops the disease at an early stage would be exactly what we people with Parkinson's are missing.

What happens next?

The trial continues with a two-year extension. In early 2027, AC Immune wants to plan the second part with the FDA, which for the first time is to test the effect on the course of the disease. So it will be several years before there are solid results.

Sources

• Parkinson's News Today: Trial of experimental Parkinson's vaccine shows positive initial results
• AC Immune: interim results of 11 December 2025 (neurofilament light chain)

Note: This article describes my personal view and is not medical advice. The vaccine is an investigational product and has not been approved.