What happened

No news is often good news, and positive developments are nearly always good news. But top COVID-19 vaccine-makers Moderna (MRNA -3.00%), BioNTech (BNTX 0.43%), and Novavax (NVAX 8.40%) saw their shares tank this week despite either announcing a positive development or having no news.

Shares of Moderna were down 10.2% for the week as of the market close on Thursday. BioNTech stock closed 18.1% lower for the week, and Novavax's shares were tumbling 16.5%. 

Neither Moderna nor Novavax announced anything that would affect their share prices. The biggest loser of the group, BioNTech, and its partner, Pfizer (PFE 0.76%), actually had a positive development. On Tuesday, the companies submitted initial data to the U.S. Food and Drug Administration (FDA) for their COVID-19 vaccine in children ages five to 11.

What caused these vaccine stocks to tank this week? Investors appear to be increasingly concerned about the impact on COVID-19 vaccine sales once life returns to normal. The CEOs of Pfizer and Moderna have stated in recent interviews that they expect the pandemic could end next year. BioNTech's co-founder, Özlem Türeci, also stated this week that COVID-19 will "become manageable," with boosters needed perhaps every 12 to 18 months.

A person wearing a facemask receiving a vaccine shot from a healthcare professional.

Image source: Getty Images.

So what

It really doesn't make a lot of sense that investors' worries about these stocks would be so pronounced this week. There's been significant uncertainty for a while about how long COVID-19 vaccine sales would hold up near current levels.

Moderna and BioNTech are entirely dependent on their respective COVID-19 vaccines for revenue. If boosters are only needed every 12 to 18 months, as Türeci anticipates, both companies' sales will likely decline quite a bit after next year.

Novavax doesn't have any vaccine sales yet. However, the lower the frequency of necessary boosters, the lower the company's long-term prospects are for its COVID-19 vaccine.

On the other hand, the delta variant has been at the forefront of news stories for a few months. The number of new COVID-19 cases in the U.S. is falling again. As concerns about the delta variant decline, worries about the future for vaccine stocks are rising.

Now what

For investors betting on Moderna, BioNTech, and Novavax, the only thing to do is wait and see what happens with the COVID-19 vaccine-market dynamics. Of the three, Novavax has the clearest catalysts. The company hopes to win Emergency Use Listing from the World Health Organization for its vaccine. It also plans to file for Emergency Use Authorizations in several countries.

Perhaps the best chance for Moderna and BioNTech stocks to bounce back is for the companies to pick up additional supply deals for 2022 and beyond. It would especially be helpful for their share prices if more major countries inked agreements for 2023 and even into 2024.

However, there's also unfortunately another way that all three stocks could again soar. The emergence of new deadly coronavirus variants would likely translate to big gains for Moderna, BioNTech, and Novavax. Bad news for the world could be good news for vaccine stocks.