Vaccination with a live multi-gene deletion strain protects horses against virulent challenge with Streptococcus equi

- A Streptococcus equi vaccine strain containing deletions in six genes was generated.
- Intramuscular vaccination protected 85% of ponies from strangles.
- Vaccinated ponies did not seroconvert to SeM, suggesting that this test could be used as a differential diagnostic.
- Adverse reactions occurred in five of nine vaccinated ponies.