Three COVID-19 vaccines are currently available to Americans. One of them, however, faces some challenges. Johnson & Johnson won't be able to supply as many doses of its vaccine in the next few weeks as originally hoped due to manufacturing issues at a contractor's facility. Questions about whether the vaccine could cause blood clots on a very rare basis have also arisen. 

With these headwinds for J&J, the vaccines developed by Moderna (MRNA 1.90%) and Pfizer (PFE 0.10%) (with its partner BioNTech (BNTX -0.43%)) are in high demand. Both vaccines have very high efficacy levels. Both Moderna and Pfizer/BioNTech have secured supply deals with the U.S. for 300 million doses each.

But new research findings appear to indicate that individuals who receive Moderna's vaccine are more likely to experience reactions and side effects. Could this latest news boost Pfizer's fortunes?

Woman wearing a face mask looking back at a healthcare professional as he gives her a shot in the arm.

Image source: Getty Images.

More side effects for Moderna

Both Pfizer's and Moderna's COVID-19 vaccines use the same approach. Messenger RNA (mRNA) is injected into the body. This mRNA contains instructions for producing proteins that are identical to the spike protein on the surface of SARS-CoV-2, the coronavirus that causes COVID-19. The body then develops antibodies and T cells that can fight the virus in the future, thereby providing protection against infection.

Because the two vaccines use this same approach, similar side effects were reported in clinical studies conducted by Moderna and Pfizer/BioNTech. The most frequent reactions included pain at injection sites, fatigue, and headache. 

The U.S. Centers for Disease Control and Prevention (CDC) has tracked data about adverse reactions for both vaccines in the agency's V-safe surveillance system. Last week, CDC scientists published an article in the online medical journal JAMA that analyzed the V-safe data recorded between Dec. 14, 2020, and Feb. 28, 2021.

This analysis showed that 73.9% of respondents in the V-safe system experienced side effects after taking the first dose of Moderna's COVID-19 vaccine. The number was lower -- 65.4% -- for individuals receiving the first dose of Pfizer's vaccine.

It was a similar story after the second dose of each vaccine. Among respondents receiving Moderna's shot, 81.9% reported experiencing side effects. For those receiving the Pfizer vaccine, 68.6% reported a reaction after the second dose.

A positive effect for Pfizer?

Pfizer has already reported slightly higher efficacy for its COVID-19 vaccine than Moderna. Is the data showing that its vaccine produces fewer side effects potentially good news for the big pharma stock? Maybe.

The U.S. already has more than enough COVID-19 vaccine doses ordered to vaccinate all Americans this year. Several other developed nations have also made large supply deals with various vaccine makers. It's possible that Pfizer could receive more orders as a result of the competitive advantages of its vaccine compared to Moderna's vaccine. However, the short-term impact for Pfizer's share price would likely be relatively small.

It could be a different story over the longer term, though. When countries aren't forced to scramble to secure vaccine doses, they could (and probably will) place greater emphasis on the efficacy and safety profiles of the vaccines they buy. That just might give Pfizer a leg up over Moderna.

A relatively modest 10% increase in doses ordered each year could translate to well over $1 billion for Pfizer. Even after splitting its profits with BioNTech, the big drugmaker would stand to rake in a lot more money if it can beat Moderna in the post-pandemic marketplace.

Changing dynamics

Don't get the cart before the horse, however. There are far too many changing dynamics in the COVID-19 vaccine space that could offset any advantage that Pfizer might have related to the latest CDC data.

Probably the most important to keep in mind is the emergence of new variants. Pfizer and BioNTech have begun testing a third booster dose of their COVID-19 vaccine. Moderna is testing a modified version of its mRNA vaccine that specifically targets the B.1.351 variant first identified in South Africa. 

Moderna's vaccine could demonstrate significantly greater efficacy against the South African variant than Pfizer's vaccine. If that happens, a slightly lower chance of adverse reactions likely wouldn't help Pfizer compete against Moderna. There's also the possibility that another COVID-19 vaccine could win authorization or approval down the road that's even more safe and effective than Pfizer's or Moderna's vaccines.  

Still, the good news keeps coming for Pfizer's COVID-19 vaccine. This could cumulatively boost investors' confidence in the stock. That's a side effect that Pfizer would love to see.