Investors are attempting to brush off comments from Federal Reserve Vice President Lael Brainard, which reignited rate hike concerns.

The Dow Jones Industrial Average is flat midday, as it cools off from this morning's burst higher. Both the S&P 500 Index and Nasdaq Composite are more comfortably in the black.

Biotech stocks reversed course and advanced solidly in the week ending Dec. 17, as an increase in risk aversion pushed investors to buy into defensive stocks. The sector also drew strength from some positive stock-specific news.

Shares of software maker Samsara rose over 7% in the stock's trading debut following a $805 million IPO. The company is the pioneer of the Connected Operations Cloud, which allows businesses to develop actionable business insights.