This is the 944th most frequent Estonian word.
viiruse
The Estonian word "viiruse" means "of the virus" in English.
In this sentence, 'viiruse' is again in the genitive case, used here for specifying 'strains of the virus' as a characteristic of the strains.
Arstid uurivad viiruse uusi tüvesid.
Doctors are studying new strains of the virus.
Here, 'viiruse' is in the genitive case, used in the phrase 'kaitseb viiruse eest' to specify the entity against which the protection is focused.
Me saime vaktsiini, mis kaitseb viiruse eest.
We received a vaccine that protects against the virus.
Here, 'viiruse' is in the genitive case, indicating possession or relation, showing the 'spread of the virus'.