Aug 12 (Reuters) - Airbnb Inc (ABNB.O) on Thursday warned of an adverse impact to its bookings due to the Delta variant of the coronavirus and a slowing pace of vaccination in the United States, sending its shares down more than 4%. The company expects nights and experiences booked - a measure of the number of nights and seats for experiences booked on the platform - in the current quarter to slow from the second quarter and remain below 2019 levels. The hugely popular global app, which has fought back strongly since being hit hard early in the pandemic last year, posted a more than four-fold rise in bookings to $13.4 billion in the second quarter. It expects the third quarter to be its strongest on record as more people check into its vacation rentals after the easing of COVID-19 curbs in most major economies. Active listings have been roughly stable throughout the health crisis and grew during the quarter, especially in non-urban destinations across Europe and North America, the company said. "In Q3, we are starting to see the global spread of COVID variants, a patchwork of local travel restrictions and slowing vaccinations adversely impact cancellations and growth of Nights and Experiences Booked," the company said. Hotels and other accommodation providers took a hammering last year as COVID-19 travel restrictions shut down large parts of their business. Airbnb drew plaudits, however, for shifting its focus quickly to local and long-term rentals, attracting people looking for accommodations to rent for remote working or which did not require flying. The company expects to report record third-quarter adjusted income before interest, taxes, depreciation and amortization (EBITDA) and margin. Its gross bookings surpassed Refinitiv IBES estimates of $11.34 billion. Revenue tripled to $1.34 billion in the quarter, beating estimates of $1.26 billion. The company"s loss of 11 cents per share was smaller than analysts" estimate of 47 cents.