Treasury Inflation-Protected Securities (TIPS) and gold have lured investors, who reckon unprecedented monetary and fiscal stimulus will eventually produce higher prices. In June alone, investors poured a record $6 billion into TIPS according to Lipper data, while an ICE BofA index of inflation-linked securities has rallied almost 20% this year <.MERG9QI>.

Recent polls though indicate the pandemic's legacy could actually be weak or falling prices.

"Our opinion is that the economic data is a lot muddier than people give it credit for," said Scott Kimball, a portfolio manager at BMO Global Asset Management, who is not bullish on TIPS. "A deflationary environment is closer than people think."

Yields on 10-year TIPS , or real yields as they are adjusted for inflation, tumbled recently to the lowest on a closing price basis since 2012, which preceded the so-called taper tantrum, and stand currently at minus 0.849%.

That is down around 30 basis points since early-June, while nominal yields are around 5 basis points lower over the same period. Thirty-year TIPS are near record lows.

The Fed too has contributed, buying $134 billion of TIPS between March 16 to July as part of its asset purchase program according to SocGen analysts.

"There is a fear that the Fed expanding its balance sheet is going to create an inflationary impulse," said Frank Rybinski, senior investment strategist at Aegon Asset Management. "I structurally don't see that right now."

The rally in TIPS reflects an uptick in inflation expectations, with breakeven rates now showing an expectation of 1.4% on average for the coming decade .

"My view is it will be difficult to see breakevens moving higher. There are structural disinflationary forces which remain as vigorous as before," Pictet Wealth Management economist Thomas Costerg said, citing technology and globalization among the factors.

Some big-name investors including Bill Gross are also not enthusiastic about the trade, saying last week that rates had "seen their best days.".

Blackrock in its mid-term outlook said it was neutral on TIPS.

"Shorter term the risks are tilted to the downside towards disinflation, even deflation ... and beyond that we see the risks flipping the other way," said Mike Pyle, global chief investment strategist at the BlackRock Investment Institute.

Deepening negative real yields are also fueling some nervousness. Fixed income trading platform Tradeweb notes negative yields can be an indication that investors believe growth "may be persistently weak and that they might as well park their money in a risk-free asset with a known real yield."

Morgan Stanley noted five-year TIPS yields could soon fall below German real yields for the first time in at least half a decade. In Germany, both nominal and real yields have been negative for years, coming after massive European Central Bank stimulus.

If COVID-19 derails the economic recovery, 10-year real rates could fall all the way to minus 150 bps in the worst case scenario, BofA analysts predicted.

Subadra Rajappa, head of U.S. interest rate strategy at Societe Generale, attributes the yields decline at least partly to investors, including hedge funds or sovereign wealth funds using them as a de facto hedge against risk. At some point, these investors might "take profits and exit the product," said Rajappa.

On a longer term horizon, investors see TIPS as a product to hold. Mark Heppenstall, CIO of Penn Mutual Asset Management, has not been adding to TIPS positions recently, but views them as a good "diversifier in a fixed income portfolio" with a unique hedging ability.

Mike Kelly, head of multi asset at PineBridge Investments said if inflation picks up, three to four years out, "gold and linkers (inflation protected bonds) will come into their own."

By David Randall and Megan Davies