LONDON, Jan 29 (Reuters) - Poor distribution of COVID-19 vaccines and prolonged lockdowns send the economy into a tailspin in this year's stress test of top European Union banks, the bloc's regulators said on Friday.

The European Banking Authority (EBA) said the combination of such theoretical shocks for the top 50 banks like Deutsche Bank, UniCredit and Santander and covering 70% of total EU banking assets, was among its toughest yet.

"It does not attempt to make any predictions about the evolution of the pandemic but leaves room for a variety of possible negative outcomes, for example ineffective vaccine distribution or mutation of the virus," EBA said in a statement.

Friday's test launch comes as the bloc's executive European Commission clashes with pharmaceutical group AstraZeneca over shortfalls in vaccine deliveries.

Vaccination is seen as crucial to ending lockdowns and reviving economic growth, but the EU lags far behind Israel, newly-departed EU member Britain and the United States.

The regular stress test is aimed at checking whether banks have enough capital to withstand shocks. It was postponed last year to allow lenders to keep credit flowing during the severe, real-life test of pandemic lockdowns.

It is the first test not to include UK lenders, and bank-by-bank results will be published in July.

"In addition, the outcome might serve as valuable input for identifying possible exit strategies from the flexibility measures granted to banks, due to the COVID-19 crisis, or for considering additional measures, should the current economic conditions deteriorate further," EBA said.

The ECB warned on Thursday that a hasty end to COVID relief measures could induce a fresh crisis that could hit companies and banks.

The test envisages a 3.6% drop in real economic growth from 2020 to 2023, with unemployment rising by 4.7 percentage points.

Residential property prices fall cumulatively by 16.1%, while commercial real estate prices sink by 31.2%, as more people work from home.

European stock prices also crash by half in the first year.

"The 2021 adverse scenario is very severe having in mind the weaker macroeconomic starting point in 2020 as a result of the severe pandemic-induced recession," EBA said.

(Reporting by Huw Jones; editing by Emelia Sithole-Matarise)