The European Central Bank’s (ECB) asset purchase plan curbs the threat of deflation, but its ability to kickstart growth remains uncertain, says Fitch Ratings.

On Jan. 22, the ECB announced a large asset purchase program that Fitch says reduces the risk of prolonged deflation in the region, by weakening the euro and boosting confidence. “But its ultimate effectiveness in raising inflation and growth remains highly uncertain,” the rating agency cautions.

Fitch says that the ECB’s plan to add sovereign bond purchases to its existing private sector asset purchase program is expected to generate combined monthly purchases of €60 billion, which are “intended” to be carried out until the end of September 2016, or the central bank sees a sustained improvement in the path of inflation.

If it goes ahead with these planned purchases until September 2016, Fitch says that the ECB would expand its balance sheet by approximately €1.14 trillion to nearly €3.3 trillion, of 33% of GDP; which would make the ECB’s program larger than the ones carried out by either the U.S. Federal Reserve and the Bank of England, as a proportion of GDP. Although, it would still be significantly smaller than the Bank of Japan’s effort.

Fitch says that the ECB’s asset purchase program should help underpin inflation expectations, boost asset prices, and lead to a weaker euro. All of this should help avoid prolonged deflation. However, it notes that as banks continue to delever and strengthen their balance sheets, their willingness to boost the supply of credit “may be less than anticipated”. Moreover, Fitch says that credit demand appears to be muted “due to high unemployment and economic uncertainty”.