What happened

Shares of Moderna (MRNA 1.58%) moving 4.5% lower as of 11:57 a.m. EST on Monday. The decline appears to be the direct result of the U.S. Food and Drug Administration (FDA) granting emergency use authorization (EUA) to Johnson & Johnson's (JNJ -1.82%) COVID-19 vaccine over the weekend.

So what

Does Johnson & Johnson's EUA make a difference for Moderna over the short term? Nope. Moderna already has an agreement with the U.S. government to supply 300 million doses of its COVID-19 vaccine. With the supply deals that the U.S. government has lined up with other companies, there will be more than enough vaccine doses to immunize all American adults this year.

Gloved hands holding two vials labeled Vaccine COVID-19

Image source: Getty Images.

The more important question is whether or not J&J's COVID-19 vaccine could take market share away from Moderna over the longer term. While Moderna's mRNA-1273 requires two doses, J&J's vaccine only requires a single dose. However, Moderna's overall efficacy appears to be significantly higher -- although it's impossible to make a truly apples-to-apples comparison because of the emergence of new coronavirus variants that were a bigger factor in J&J's late-stage study. 

New variants will likely be a key factor in Moderna's ability to retain its market share. The biotech's messenger RNA (mRNA) technology could give it an edge in rapidly developing booster shots that are effective against new coronavirus strains that might emerge in the future.

Now what

Moderna could have more good news on the way. For example, the company should report results in the near term from a phase 2/3 study evaluating mRNA-1273 in adolescents. It's also beefing up its pipeline and will soon advance cytomegalovirus (CMV) vaccine mRNA-1647 into a pivotal late-stage study. Don't be surprised if the biotech stock bounces back relatively quickly.