Delta has been in Ukraine about a month at least. Ukraine as far as I can tell doesn't have much genomic surveillance of it though at the moment, so no clue how prevalent it is. The Health Ministry expects it to become dominant before the Summer is over, which would match the US's experience with the variant.
So far cases are low. Test positivity is rising recently, but still fairly low. Hospitalizations are also low.
This could all change rapidly if other countries are any indication. Since Ukraine doesn't do a lot of testing, test positivity will likely be the best early warning indication of things going wrong.
Ukraine was hard hit by the virus, so there likely are a lot of Ukrainians with prior infection immunity. However, the country is still quite vulnerable. Delta is ~40% more transmissible than the Alpha variant, which was already ~60% more transmissible than the wild type virus. It also appears to have a higher viral load quicker than previous strains.
Reinfection risk is higher with Delta, so many of the people with prior infection immunity will nevertheless be vulnerable to infection and transmitting the virus. The UK's SIREN nurses study is seeing more healthcare workers get reinfected, particularly if they were infected earlier in the pandemic.
Only about 4% of the population is fully vaccinated. Everyone over 18 became eligible for the vaccine last week, so hopefully the rate improves. They will have enough doses for every Ukrainian by the end of the Summer.
