Emergent BioSolutions (EBS -5.59%) saw its shares tumble on Tuesday, due to news of a share sell-off. The vaccine maker divulged in a regulatory filing that several institutional share and warrant holders are selling such securities. Investors reacted by trading Emergent's stock down by almost 6%, on a day when the S&P 500 (^GSPC 0.05%) more or less flatlined.

The selling parties are mainly entities affiliated with OHA Agency, a business that provided a $250 million term loan to Emergent in August. In return for this, the vaccine maker issued slightly over 1.1 million shares of its common stock to OHA, plus 2.5 million warrants to buy said stock.

In the sale, the sellers will divest up to a bit over 3.6 million Emergent shares. That amount includes the 1.1 million issued shares, plus shares deriving from exercise of the warrants. The company said that the sales would be effected from time to time, and did not provide further details.

Emergent stressed in its filing that it will receive no monies from these sales, as it is not one of the selling parties.

In situations like this, investors are most wary of potential stockholder dilution. That, fortunately for Emergent shareholders, isn't really the case here -- the company has more than 54 million shares outstanding currently. So even in an extreme scenario, the sales won't be worryingly dilutive.

However, any decent-sized divestment risks damaging morale regarding a company's future. After all, even institutional investors are tempted to hang on in situations where a stock could potentially rise to a meaningful degree. It's no wonder the market was discouraged by news of the coming Emergent sales.