SANTA CRUZ (CBS SF/BCN) — County health officials announced Tuesday that a case of the highly contagious Delta Variant of the coronavirus has been confirmed in a fully vaccinated Santa Cruz County resident.

The patient, a man in his 50s, experienced mild symptoms and has recovered since his sample was taken June 10. An investigation into the case is ongoing, but health experts have noted that a handful of such breakthrough cases are to be expected.

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The Delta Variant, which was first detected in India, has been found in more than 80 countries and is believed to be some 60 percent more transmissible than the alpha variant, also known as the UK or B.1.1.7 variant.

Roughly 15 percent of COVID-19 cases in California are Delta Variant cases and the variant is likely to become the dominant strain in the U.S. as the year progresses, particularly among unvaccinated people.

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For fully vaccinated people, health experts say the available vaccines from Moderna, Pfizer-BioNTech and Johnson & Johnson are highly effective against the Delta Variant, providing protection from death and serious illness in the 80-90 percent range.

Health officials said that the first dose of the two-dose Moderna and Pfizer vaccines is less effective against the Delta Variant than previous variants, and people who have only received their first of two shots are urged to get fully vaccinated as soon as possible.

Santa Cruz County Deputy Health Officer Dr. David Ghilarducci said the Delta Variant’s confirmation locally is all the more evidence to get vaccinated against the coronavirus.

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“With the reopening of the economy and slowing vaccination rates, the introduction of a highly transmissible variant creates an especially worrisome situation,” Ghilarducci said in a statement. “For those who are unvaccinated or only partially vaccinated, your risk of serious illness is becoming more likely.”