Israel Had a 100% Protective mRNA Plague Vaccine in Mice Before Russian Lab Technician Died

Israeli researchers reported complete protection against pneumonic plague in specified mouse experiments in 2025, more than a year before a Russian anti-plague laboratory employee died from an unexplained illness. The experimental mRNA vaccine was developed by researchers at Tel Aviv University and the Israel Institute for Biological Research.

The findings, published in 'Advanced Science' on 25 April 2025, concern animal research rather than demonstrated protection in people. Russian authorities have not confirmed that the deceased worker had plague, and the research does not establish that the vaccine could have prevented her death.

Two Antigens Target Plague Bacterium

The experimental vaccine targets Yersinia pestis, the bacterium that causes plague. Pneumonic plague affects the lungs and can spread between people through respiratory droplets during close contact.

The researchers developed two messenger RNA constructs targeting bacterial proteins known as F1 and LcrV. The combined approach is described as bivalent because it targets two antigens, substances that the immune system can learn to recognise.

The mRNA was delivered in lipid nanoparticles, tiny fat-based carriers that help transport it into cells. Rather than administering the whole bacterium, the approach gives cells instructions to produce antigen material that can stimulate an immune response.

The paper examined whether that response could protect mice when they were subsequently exposed to the plague bacterium. It was a preventive vaccination experiment, not a test of treatment for animals already seriously ill.

Study Reports Mouse Results Only

The researchers tested the vaccine in several strains of mice exposed to Yersinia pestis. After two doses, survival ranged from 87.5% to 100% across the mouse strains studied.

After three doses, all vaccinated mice in the tested groups survived the experimental pneumonic-plague challenge. These results are encouraging preclinical findings, but they do not establish protection in people or guarantee that the same response would occur outside laboratory conditions.

The peer-reviewed paper is titled 'Novel Bivalent mRNA-LNP Vaccine for Highly Effective Protection against Pneumonic Plague'. Its findings provide evidence for further development of the approach, but the publication does not report a human efficacy trial.

The phrase '100% protective' therefore describes survival in tested mouse groups after a three-dose regimen. It is not a clinical guarantee or an established option for people exposed to plague.

The study also does not show that the experimental vaccine was available to Russian laboratory staff or that it was offered to the deceased employee.

Russian Death Remains Unexplained

Reports identified the Russian worker as Darya Shipilova, an employee of the Irkutsk Anti-Plague Research Institute of Siberia and the Far East. She was reportedly admitted to hospital on 29 September and died in early October.

The institute is based in Irkutsk, while reporting placed her hospital treatment in nearby Shelekhov. Her employment at a plague research institute does not establish that she acquired an infection at work.

Russia's public-health agency, Rospotrebnadzor, said on 4 October that the employee had been diagnosed with 'pneumonia of unknown aetiology', meaning pneumonia whose cause had not been identified.

The agency said testing detected no micro-organisms associated with her professional activities and that no accident involving pathogenic micro-organisms had been identified at the institute.

Regional media reported that nearly 200 contacts were placed under medical observation. That figure concerned people being monitored, not confirmed plague infections.

On 5 October, Irkutsk Governor Igor Kobzev said identified contacts were not showing symptoms and their laboratory tests were negative. The US State Department said it was monitoring reports of a suspected pneumonic-plague death while stressing that many details remained unconfirmed.

Prompt Antibiotics Remain Essential

Plague is a serious bacterial infection, but prompt antibiotic treatment can be effective. The US Centers for Disease Control and Prevention advises clinicians to begin appropriate treatment as soon as plague is suspected rather than wait for confirmatory laboratory results.

An experimental preventive vaccine is not a substitute for that treatment advice. Nor does the existence of promising animal research establish what caused an individual's illness or whether a particular intervention would have changed its outcome.

The Israeli findings concern a potential vaccine supported by mouse experiments. The Russian case concerns an unexplained fatal illness under investigation; the available evidence does not establish a medical connection between them.