question: Objective: COVID19 was declared a global pandemic by the WHO in March, 2020 and lockdown was imposed to a third of the world’s population. Now, determining the transmission potential and immune status among sheltering in place asymptomatic patients and clinical staff resuming their activity is crucial. Here, we report herd immunity, infective, and naïve incidence for SARS-CoV-2 after the lockdown period, among asymptomatic medical personnel and patients in two US ART centers located in states with different COVID19 incidences. Design: Prospective multicenter study (ClinicalTrials.gov NCT04466644). Materials and Methods: A total of 339 asymptomatic individuals (personnel and patients) were analyzed from June 18 to July 30, 2020 in two ART centers reopening after lockdown following CDC safety guidelines. In Clinic A (Utah Fertility Center), located in a low prevalence State (312 cases per 100,000 on 06/01/2020), 154 individuals were analyzed. In clinic B (Boston IVF), in a high prevalence scenario (Massachusetts, 1,462 cases per 100,000 on 06/01/2020), 185 individuals were tested. Asymptomatic individuals attending or working in the indicated clinics were tested by RT-PCR on nasopharyngeal swab for SARS-CoV-2 RNA detection (Thermofisher, Waltham, MA, USA), and for IgG quantification on blood samples (Abbott Inc, Scarborough, ME, USA), following FDA-Emergency Use Authorization protocols. IRB approval was obtained from WIRB Protocol #20201490. Results: From 339 asymptomatic individuals tested, the percentage of non-informativity was 0 for RT-PCR and 0.6% (2 out of 339) for the IgG test. Only those individuals with informative results for both tests (n= 337) are presented. [Formula presented] Conclusions: In the population investigated, our results suggest that the impact of the pandemic is far from reaching the level required to achieve herd immunity (i.e., 50% of a population). Therefore, transmission remains a risk since potential infectivity is present in 0.6% of the asymptomatic population tested. This figure was maintained despite their different geographical locations and the adherence to CDC guidelines of the IVF clinics involved. Interestingly, the two PCR+ individuals were IgG + suggesting virus persistence or reinfection that, if tested by serology alone, would be considered immune. These results together with the high incidence of naive individuals draws attention for the implementation of a consistent program of testing for COVID19 as a means of preventing reemerging outbreaks in our fertility centers.