The dollar was on the defensive against its rivals on Wednesday as traders looked to Federal Reserve Chairman Jerome Powell’s speech amid rising speculation the United States could one day adopt negative interest rates.

Risk-sensitive currencies lacked momentum as a warning from a top U.S. health official about the dangers of reopening the economy too soon served as a reminder of the uncertainties facing an economy which has been ravaged by the novel coronavirus.

The dollar traded at 107.15 yen, having slipped from Tuesday’s peak of 107.76, its highest since April 24.

The euro changed hands at $1.0848 after having gained about 0.4 percent in the previous session.

U.S. President Donald Trump on Tuesday again pushed the Federal Reserve to adopt negative interest rates, a hot topic in financial markets since last week when U.S. money market instruments started to price in a chance of negative rates.

U.S. consumer prices dropped 0.8 percent in April, the biggest since the Great Recession, raising the specter of deflation as the economy sinks deeper into recession and fueling the debate about policy responses.

“I would advise against negative rates. Japan has done that but the perception here is that it wasn’t so good,” said Hiroyuki Ueno, senior strategist at Sumitomo Mitsui Trust Asset Management.

“But what’s worrying is that Trump is now talking about them. Looking at past examples, the Fed has eventually done what Trump wanted quite often.”

Powell will be speaking on current economic issues in a webcast hosted by the Peterson Institute for International Economics at 9:00 a.m. (1300 GMT).

Although Fed officials have said they do not see a need to cut interest rates below zero--investors think that will become an option especially if the coronavirus outbreak leads to further deterioration in the U.S. economy.

Top U.S. infectious disease adviser Anthony Fauci on Tuesday warned Congress that a premature lifting of lockdowns could lead to additional outbreaks of the deadly coronavirus.

His comments cast a shadow on optimism in financial markets in recent weeks that the worst period of the epidemic is over and the economy can only get better.

U.S. stock prices also slid, led by high-flying technology shares, adding to the cautious mood on the economic outlook.

That put a brake on a rally in risk-sensitive currencies such as the Australian dollar.

The Australian currency stepped back to $0.6473 from Monday’s one-week high of $0.6562.

It took an additional hit on Tuesday after China banned some Australian meat imports, though it trimmed losses later as Australia’s trade minister played down the issue as a technicality.

The New Zealand dollar stood at $0.6082, down so far in the week but inside its recent trading range ahead of a policy announcement from the country’s central bank later in the day.

The Reserve Bank of New Zealand is expected to keep interest rates on hold at 0.25 percent while expanding its quantitative easing program.

The British pound stood near its lowest levels in five weeks at $1.2264, pummeled also by continued confusion over government plans to ease lockdown measures, the worst COVID-19 death toll in Europe and revived Brexit risks.

Official data published on Tuesday showed Britain’s death toll from COVID-19 topped 38,000 as of early May, having overtaken Italy as the worst affected country in Europe.