What happened

Shares of Pfizer (PFE 2.40%) were up 2.5% as of 11:35 a.m. ET on Friday after jumping as much as 4% earlier in the day. Meanwhile, the stocks of two other COVID-19 vaccine makers were declining. Moderna's (MRNA -0.58%) shares were down 4.7%. Novavax (NVAX 2.06%) stock was sinking 7.9% lower.

Why was Pfizer rising while Moderna and Novavax were sliding? Although they're all vaccine stocks, they each have very different dynamics impacting their share prices.

Pfizer is still basking somewhat in the glow of good news from Tuesday. The U.S. Food and Drug Administration (FDA) granted Emergency Use Authorization (EUA) to booster doses of the company's COVID-19 vaccine in children ages 5 to 11.

Neither Moderna nor Novavax has benefited from positive catalysts this week. With the overall stock market again slipping, both stocks appear to be caught up in the downdraft. Novavax tends to fare worse during such declines than Moderna does. This is mainly due to the greater uncertainties that the company faces with its COVID-19 vaccine.

So what

Investors probably shouldn't read too much into today's moves for any of these stocks. That's especially the case for Moderna and Novavax. The two companies' prospects are no worse (and no better) now than they were earlier this week.

Even Pfizer's good news isn't anything to get overly excited about. It's unlikely that the EUA for boosters in young kids will lead to any additional orders of doses of the company's vaccine over the near term.

More than 8 million children ages 5 through 11 in the U.S. have received the primary two-dose series of the Pfizer-BioNTech vaccine. However, even if all of them now get a booster dose, Pfizer probably won't secure any new orders. The U.S. government already has a supply deal with Pfizer and BioNTech for 600 million doses but has delivered only around 433 million doses of the two companies' vaccine. 

A healthcare professional giving a shot to a child.

Image source: Getty Images.

Now what

Novavax probably has the most upside potential in the short term among these three stocks. The FDA has scheduled an advisory committee meeting for June 7 to review the company's EUA filing for its COVID-19 vaccine. 

It seems likely that Novavax's shares will pop if the advisory committee gives its blessing and the FDA follows up with authorization. The chances of this positive scenario playing out seem to be pretty good at this point.

Moderna hopes to soon receive U.S. EUA for a booster dose of its COVID-19 vaccine in kids ages 6 to 11. The company also expects to report initial data in June for its bivalent COVID-19 vaccine candidate that combines its already-approved mRNA-1273 vaccine and a version targeting the coronavirus omicron variant. 

Pfizer will be closely watching for a thumbs-up from the FDA on Biohaven's regulatory filing for migraine drug zavegepant. The big drugmaker announced earlier this month that it plans to acquire Biohaven for $11.6 billion. The transaction is expected to close by early 2023.