The Swiss stock index jumped over 1% on Wednesday after Roche surged on positive lung cancer drug trial data, while other European averages lagged behind as more data hinted at slowing economic activity in the continent.

The Swiss Market Index added 1.1%, touching its highest level in a week, while the pan-European STOXX 600 rose 0.6%, set for its third straight session of gains.

Roche jumped 4.3% after the Swiss drugmaker inadvertently released the data, which was perceived as a positive even though more information is needed to confirm the treatment's efficacy.

The broader healthcare index added 0.9%.

On the data front, German business activity contracted at the fastest pace in more than three years in August, while France's dominant services sector contracted further in August, a preliminary survey showed.

Separately, a 'flash' estimate showed the downturn in euro zone business activity has deepened far more than thought this month, leading to traders scaling back bets for a September interest rate hike.

"The ECB's hopes for an economic recovery in the second half of the year have received another bitter blow with today's data," said Christoph Weil, senior economist at Commerzbank.

German 10-year bund yields, considered Europe's benchmark, eased, while rate-sensitive real estate stocks added 1.8%.

This week's centrepiece is the Jackson Hole Symposium, where speeches by European Central Bank President Christine Lagarde and Federal Reverse Chair Jerome Powell will be scanned for clues on future monetary policy.

Despite recent gains, the pan-European benchmark is headed for its worst month this year as elevated bond yields weighed on equities.

Meanwhile, second-quarter earnings for European firms are now estimated to have fallen 5%, slightly higher than the 4.6% drop estimated last week, Refinitiv data showed.

Among individual stocks, Orsted added 3.0% after the U.S. Interior Department approved the construction of a 704 megawatt (MW) wind farm off the coast of Rhode Island.

Bavarian Nordic surged 10.9% to the top of the STOXX 600 after the Danish biotech company beat second-quarter revenue expectations.

Societe Generale rose 2.0% after Morgan Stanley upgraded the French bank to "overweight" from "equal-weight." (Reporting by Shashwat Chauhan in Bengaluru; Editing by Varun H K and Savio D'Souza)