Johnson & Johnson, for example, posted a 20 percent gain between March 23 and March 30, and ended the month down less than 3 percent. But the medical equipment manufacturer Stryker declined 23.5 percent.

Another reason broad holdings make sense is that even if a fund does end up holding one or more companies that develops an effective Covid-19 vaccine, anti-viral drug or home virus test, those specific investments may not end up being home runs, said Chris Cordaro, chief investment officer at RegentAtlantic.

“If Company X develops a treatment and it’s $1,000 a dose, will they really be able to charge a premium price?” Mr. Cordaro said. “So it’s probably not going to be a great moneymaker.”

The crisis also gives biotech and pharma development companies a chance to restore their badly stained reputations, said Brad Loncar, chief executive of Loncar Investments and creator of two biotech funds, the Cancer Immunotherapy E.T.F. and the China BioPharma E.T.F. “Things like drug pricing and the opioids epidemic have rightfully angered the public and tarnished the industry’s image. This is a big opportunity to get all of that back,” Mr. Loncar said.

Broad health care funds can be a defensive strategy, but for bargain hunters, the medical sector isn’t the place to look, said Mr. Cordaro.

“Large health care funds haven’t gone down that much, so if you’re looking for a safer place in the market, this would be it,” Mr. Cordaro said. “But if you’re looking for a pop off the bottom, you’re not going to get it.”

Mr. Cordaro said the biggest gains are more likely to come from small-capitalization funds, where concerns about limited liquidity sent investors heading for the exits. These include real estate investment trusts and funds such as the iShares Core S&P Small-Cap E.T.F., which tracks the S&P Small-Cap 600 index, and the DFA U.S. Small-Cap Value Portfolio Institutional Class, which focuses on securities of small-cap U.S. companies, Mr. Cordaro said.