Small is better for vaccine shares

Investors who bet on success in the race to develop coronavirus vaccines are finding that smaller is better.

Shares of BioNTech SE, the German startup that’s working with U.S. drug giant Pfizer Inc. to develop an innoculation, have almost tripled this year while its partner has slipped about 1%. And Moderna Inc., which went public less than two years ago, is up fivefold. AstraZeneca Plc, meanwhile, has gained 5.2%.

While all of those companies reported success this month in developing shots against the coronavirus, headline-grabbing news on a highly anticipated product just isn’t enough to boost shares of businesses as large as Pfizer and AstraZeneca -- even when they’re working on one of the most important vaccines ever.