Shareholder activism is expected to rebound next year, as the impact of the Covid-19 pandemic saw the overall number of companies targeted in 2020 fall by about 20 percent compared with the previous year.

Through December 15, there were a total of 181 campaigns launched this year by shareholder activists against companies with a market valuation of $1 billion or more, according to data compiled by Bloomberg. That's down from 226 launched in all of 2019. The numbers may change as new campaigns are launched in the second half of December.

The decline was largely due to the outbreak in the U.S. of the coronavirus in March, which would typically be the peak of the proxy season, according to Andrew Freedman, co-chair of the shareholder activism practice at the law firm Olshan Frome Wolosky LLP. Olshan was the top legal adviser on activist situations in 2020, the data show.