Introduction: More than 300 million people have been vaccinated against Covid-19 in the United States. It is well known that breakthrough infections are common in vaccinated individuals. Depending upon patient age, immunity, comorbidities, drugs, and history of Covid-19, these infections could be mild or severe and, in some cases, may require hospitalization. Objectives: To study the rate of Covid-19 breakthrough infections and associated illness in individuals after receiving mRNA vaccine. Methods: De-identified administrative claims data between December 2020 to March 2021 were used to identify vaccinated individuals (≥18 years). The study considered vaccines that were available in the US at the time of study duration. The first vaccination date was defined as index. Members were followed for two months post index to identify Covid-19 breakthrough infections (as defined by CDC) occurring ≥14 days post index. Patients with continuous enrollment for 90 days post-index were included. Evidence of vaccination was identified using pharmacy claims, while medical claims were used to identify a breakthrough and associated acute respiratory illnesses. Descriptive analysis was conducted to identify patient demographics, geographic location and age and sex wise distribution. Results: A total of 772,222 members had at least one claim for Covid-19 vaccination. Of these, 4631 (males: 1795 and females: 2836) had breakthrough infections with 384 patients reporting associated acute respiratory illness (pneumonia: 213;Acute Respiratory Distress Syndrome: 18;Acute Bronchitis: 10;Upper and Lower Respiratory Tract Infections: 128 and 16, respectively). Conclusions: Unarguably, mass vaccination has helped in reducing the burden of Covid-19 infection. However, viral vaccines are known to provide limited protection and some people may still get infected. Further research is needed to understand nature of emergency visits and conditions that call for ICU or non-ICU hospitalizations
POSC419 Examining the Rate of COVID-19 Breakthrough Infections in Individuals Who Received mRNA Vaccine in the United States