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* Apple to launch four new iPhone models at virtual event
* Amazon up as two-day 'Prime' shopping event gets underway
* Boeing slips on more 737 MAX cancellations, fall in deliveries
* Indexes: Dow fell 0.35%, S&P dips 0.31%, Nasdaq up 0.16% (Adds comment, details; updates prices)
By Medha Singh and Shivani Kumaresan
Oct 13 (Reuters) - The Dow and the S&P 500 fell on Tuesday after a four-day winning streak as a pause in Johnson & Johnson's COVID-19 trial triggered concerns about the timing of a vaccine, although a rally in technology shares supported the Nasdaq.
Johnson & Johnson shed 2% as it said it would take "a few days" to review its halted clinical trial following an unexplained illness in a study participant, possibly delaying results on one of the most closely watched efforts to contain the global pandemic.
The S&P healthcare index slipped from a record high hit in the prior session and weighed on broader markets as vaccines are seen critical to stopping the pandemic, which has driven the economy to its worst recession in decades.
Some of the worst-hit companies due to the pandemic - cruise line operators Carnival Corp, Norwegian Cruise Line Holdings and hotel operator Wynn Resorts Ltd - fell between 3% and 7%.
The J&J news is "an excruciating reminder of the difficulties that the coronavirus has brought on the economy," said Eric Schiffer, chief executive officer of private equity firm Patriarch Organization.
Adding to the negative tone, U.S. House Speaker Nancy Pelosi rejected President Donald Trump's latest offer on COVID-19 stimulus, the latest sign that a bipartisan deal on coronavirus relief remains unlikely ahead of the November election.
Hopes of more U.S. fiscal aid and a rally in tech heavyweights led stocks higher on Monday, bringing the benchmark S&P 500 and the tech-heavy Nasdaq within 2% of their record highs hit in September after a pullback last month.
Apple Inc slipped 1.1% ahead of a virtual event starting 1 p.m. ET (1700 GMT) where it is widely expected to unveil four new iPhone models.
Amazon.com Inc shares, which have already surged 86% this year, added 1% as the company began 48 hours of promotions as part of "Prime Day" in an early start to the holiday shopping season.
Kicking off third-quarter earnings season, JPMorgan Chase & Co and Citigroup surpassed analyst estimates for quarterly profit on a surge in trading revenue.
However, Citi's results underscored deeper troubles in its consumer bank that struggled with a decline in customers and spending, sending its shares down 4%. JPMorgan was also down 1.1%, while the S&P 500 bank index shed 2%.
Overall, analysts expect third-quarter earnings for S&P 500 firms to slide 19.6% from a year earlier, smaller than a 31% tumble in the prior quarter.
At 12:28 p.m. ET, the Dow Jones Industrial Average was down 0.35% at 28,735.90 and the S&P 500 was down 0.31% at 3,523.23. The Nasdaq Composite was up 0.16% at 11,894.92.
Boeing Co dropped 2% as it lost another three orders for its grounded 737 MAX jet in September and delivered half the number of aircraft from the same month a year earlier.
Declining issues outnumbered advancers for a 2.33-to-1 ratio on the NYSE and for a 1.64-to-1 ratio on the Nasdaq.
The S&P index recorded 36 new 52-week highs and one new low, while the Nasdaq recorded 94 new highs and eight new lows. (Reporting by Medha Singh in Bengalurua and Shivani Kumaresan; Editing by Saumyadeb Chakrabarty and Anil D'Silva)