INTRODUCTION Omicron cases are surging in a pandemicweary US population. As breakthrough infections increase, and with just about a quarter of the US vaccinated population having received a booster dose, adherence to non-pharmacological anti-contagion measures is critical. We examined prevalence, trends, and correlates of adherence to non-pharmacological anti-contagion measures. METHODS We used cross-sectional data from six cycles of the Household Pulse Survey during April–July 2021. The Pulse Survey is a telephone-based survey of adults aged ≥18 years in all 50 US states and D.C. Between 66262 and 78467 US adults completed each survey cycle (pooled n=425460). RESULTS During the most recent cycle analyzed (23 June–5 July 2021), 13.6% of US adults reported ever COVID-19 diagnosis, ranging from 5.0% in Hawaii to 20.5% in North Dakota; in New York State, prevalence was 14.0%. Overall, 80.9% reported having received ≥1 dose of a COVID-19 vaccine during 23 June–5 July 2021, ranging from 93.5% in D.C. to 60.1% in Wyoming; in New York State, prevalence was 83.0%. Within trend analysis over the six survey cycles (14 April–5 July 2021), the percentage of vaccinated adults who reported ‘I have decreased prevention behaviors since getting a vaccine’ increased from 10.1% at baseline during 14 April–26 April 2021, to 52.5% during 23 June–5 July 2021 (p<0.01). Significant increases occurred in all 50 US states and D.C. Those with reduced adherence were more likely to be males, more educated, married, younger, living in the Midwest, and residing in a one-family house. CONCLUSIONS During April–July 2021, the percentage of vaccinated US adults reporting reduced adherence to public COVID-19 prevention behaviors increased five-fold, suggesting growing fatigue with COVID-19 prevention measures, with major implications for community spread from omicron and possibly future variants. Intensified efforts to increase vaccine coverage, including booster doses, may benefit public health.