3 June 2025

Rocketvax Achieves Major Breakthrough in Live-Attenuated SARS-CoV-2 Vaccine Development

Basel, Switzerland − Rocketvax AG, a next-generation vaccine company and subsidiary of Swiss Rockets AG, announced a major scientific milestone in the development of its live-attenuated SARS-CoV-2 vaccine candidate, OTS-228. Developed under the scientific leadership of Professor Dr. Volker Thiel, Chief Scientist of Rocketvax and Professor of Virology at the University of Bern, the vaccine has demonstrated exceptional safety, efficacy, and genomic stability in preclinical animal models. These studies were conducted in collaboration with the Friedrich-Loeffler-Institut (FLI), Germany’s Federal Research Institute for Animal Health. The general ability to induce transmission-blocking immunity and broad protection even against SARS-CoV-2 variants Omicron BA.2, BA.5, and XBB.1.5 was demonstrated already earlier.

The preclinical data were published on 23 May 2025 in npj Vaccines, published by Nature Portfolio, in an article titled “Live attenuated SARS-CoV-2 vaccine OTS-228 demonstrates efficacy, safety, and stability in preclinical model.”

Key Findings:

  • OTS-228 shows excellent safety and high efficacy in Syrian hamster models.
  • Maximum dose trials confirm full attenuation and prevention of virus spread.
  • Serial in vivo passages reveal no reversion to virulence and high genomic stability.
  • Maintains efficacy and attenuation even after 15 in vitro passages.
  • Protective dose 50 (PD₅₀) established at <100 TCID₅₀ per hamster in low-dose challenge infection.

The vaccine was scientifically conceived and designed by Professor Dr. Volker Thiel, one of the world’s leading coronavirus researchers:

“OTS-228 is the result of years of coronavirus research and rational vaccine design,” said Professor Thiel. “Live-attenuated vaccines can offer long-lasting and broad immunity, and our data show that OTS-228 has the potential to become a safe and effective tool against current and future SARS-CoV-2 variants.”

The preclinical studies were conducted at the Friedrich-Loeffler-Institut under the direction of Professor Dr. Martin Beer, Director of the Institute of Diagnostic Virology. 

Leading the partnership efforts, Dr. Natasa Cmiljanovic, Chief Operating Officer of Rocketvax, added:

“This successful collaboration with the University of Bern and the Friedrich-Loeffler-Institut has been pivotal. The robust preclinical results validate our live-attenuated vaccine platform and position Rocketvax to advance into clinical development. We are committed to making this innovative vaccine available as a global public health solution.”

In addition, Rocketvax has entered a strategic partnership with Emergent BioSolutions, a publicly traded U.S. biotech company, to commercialize Rocketvax vaccines in the U.S. The alliance leverages Emergent’s manufacturing infrastructure and regulatory experience to accelerate worldwide access to Rocketvax’s COVID-19 vaccine platform.Rocketvax is making significant progress in the development of its lead candidate and is preparing for the regulatory submissions to launch first-in-human clinical trials. Discussions with investors, public health agencies, and strategic partners are actively underway to support the next development phase.

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