What happened

Shares of Moderna (MRNA 3.06%) had slid 4.2% lower at 11:26 a.m. ET on Tuesday after being down as much as 5.8% earlier in the day. The company didn't announce any negative news. However, there were a couple of factors that could be behind the decline.

Today's move could be at least partially due to profit-taking after Moderna's shares rose on Monday. The vaccine stock gained more than 3% yesterday after the United Kingdom's Medicines and Healthcare Products Regulatory Agency authorized Moderna's bivalent COVID-19 booster targeting the coronavirus omicron variant.

Investors could also be unhappy with Merck's (MRK -0.15%) collaboration with Orna Therapeutics to develop circular RNA (oRNA) therapies. Researchers have found that oRNA molecules have greater stability for use in in vivo (in the body) therapies than linear messenger RNA (mRNA). Merck was an early investor in Moderna but sold all its shares in 2020.

So what

Is today's decline anything for investors to seriously worry about? Not really. It's probably just noise for a relatively volatile stock.

In particular, it's too early to know if Merck's collaboration with Orna will present a threat to Moderna. Orna doesn't have any programs in clinical testing yet.

Also, Merck continues to work closely with Moderna on one program. The two companies are partnering on the development of personalized cancer vaccine mRNA-4157 in combination with Merck's cancer immunotherapy Keytruda. 

Now what

The main thing to watch with Moderna going forward is its progress in winning additional approvals and authorizations for omicron boosters. Moderna hopes to launch its bivalent omicron booster in the U.S. this fall.