In July, more than 200 hospital employees tested positive for COVID-19.The majority of the staff were vaccinated, and showed mild to moderate symptoms.In breakthrough cases, the Delta variant can also spread to vaccinated individuals.10 Things in Politics: Keep up to date with the most recent political and economic news. Loading Something is loading. Click Sign up to receive marketing emails and other offers from Insider.The New York Times reported that hundreds of employees at two San Francisco hospitals tested positive for coronavirus in July. Most of these were breakthrough cases of the highly infectious Delta variant.According to the University of California San Francisco Medical Center, 183 of 35,000 employees were infected. 84% of those infected were fully vaccinated and only two staff members who had been vaccinated needed hospitalization.Zuckerberg San Francisco General Hospital had at least 50 infected staff members, out of the 7,500 total. 75 to 80% of those hospital workers were vaccinated. None of these staff members required hospitalization.Dr. Lukejohn Day, chief medical officer at UCSF, said that the numbers from his hospital demonstrated how effective and important vaccinations are."What we are seeing is exactly what the data from vaccines showed us: COVID can still be contracted, potentially. Day stated that if you do get it it is not serious.Day also stated to ABC7 News that at most 99% of cases at UCSF could be traced back via community spread. However, hospital officials continue to investigate and conduct contact tracing.He said that the majority of cases had mild to moderate symptoms and some were completely unsymptomatic. He stated that the cases were shared among doctors, nurses, ancillary staff, and other healthcare professionals.He said, "We kind of are seeing it across the board." "We have not yet detected any patient-to staff or patient-to-staff transmission."In internal documents, the US Centers for Disease Control and Prevention stated that the highly contagious Delta variant was more transmissible than viruses that cause the common cold, Ebola, and smallpox. It is also equally contagious as chickenpox.In breakthrough cases, the Delta variant can also spread to vaccinated individuals. The agency recommended this week that everyone be covered indoors in high-transmission areas.The CDC stressed that vaccination is still highly beneficial and a critical component of fighting the coronavirus, even the Delta variant.Rochelle Walensky, Director of CDC, stated Tuesday that vaccinating children continues to prevent serious illness, hospitalizations, and even death.