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Moderna’s mRNA vaccine for RSV approved by the FDA

I know this will cause the anti-vaccine world to lose a few neurons, but here we go, the FDA has approved a new mRNA vaccine from Moderna to prevent respiratory syncytial virus (RSV). Of course, it is safe and effective, but that’s probably not going to prevent a long list of negative comments about it.

We already have RSV vaccines, and it will take time to gather data to determine whether one is the best and safest. Right now, clinical trial data shows that they are all safe and very effective.

Let’s take a quick look at this new vaccine.

a sick man covering his mouth mRNA RSV vaccine
Photo by cottonbro studio on

What is RSV?

The respiratory syncytial virus is a common, contagious virus that causes infections of the respiratory tract. It is a single-stranded RNA virus, and its name is derived from the large cells known as syncytia that form when infected cells fuse.

It usually causes mild, cold-like symptoms and resolves itself quickly. However, it can cause serious lung infections, especially in infants, older adults, and people with certain chronic medical conditions, such as diabetes. For seniors, RSV infections are dangerous as immune systems weaken.

RSV spreads from person to person through:

  • The air by coughing and sneezing.
  • Direct contact, such as kissing the face of a child who has RSV.
  • Touching an object or surface with the virus on it, then touching your mouth, nose, or eyes before washing your hands.

(I don’t mean to keep repeating myself, but all the measures you take to reduce your risk for COVID-19 seem to be useful for preventing RSV.)

RSV can sometimes lead to pneumonia (infection of the lungs) and congestive heart failure (when the heart can’t pump blood and oxygen to the body’s tissues).

According to the CDC, each year in the United States, RSV leads to approximately—

  • 2.1 million outpatient visits among children younger than 5 years old
  • 58,000 hospitalizations among children younger than 5 years old
  • 177,000 hospitalizations among adults 65 years and older
  • 14,000 deaths among adults 65 years and older

I know these numbers pale next to COVID-19, but before the pandemic, an RSV vaccine was often at the top of the wish list for a new vaccine. And for those people who had children or parents who had to deal with a serious RSV case, they probably wish there was a vaccine too.

There were two versions of the RSV vaccine available before this new mRNA vaccine — Arexvy from GSK and Abrysvo from Pfizer.

There is also a pediatric RSV vaccine recently approved by the FDA and recommended by the CDC for all infants under the age of 8 months. The CDC is also recommending the vaccine for children between the ages of 8 and 19 months who are at increased risk of severe RSV disease. The vaccine, called Beyfortus, is widely available now.

close up view of person holding a vaccine
Photo by Karolina Kaboompics on

New mRNA vaccine for RSV

The new mRNA vaccine for RSV, called mRESVIA, consists of an mRNA sequence encoding a stabilized prefusion F glycoprotein, which is expressed on the surface of the respiratory syncytial virus. This glycoprotein is required for infection by helping the virus to enter host cells. The vaccine uses the same lipid nanoparticles (LNPs) as the Moderna COVID-19 vaccines.

The FDA’s approval of the new mRNA vaccine for RSV was based on the results of the ConquerRSV trial published in the New England Journal of Medicine on 14 December 2023 by Eleanor Wilson, MD, and colleagues.

The trial enrolled approximately 37,000 adults, ages 60 years and older, divided equally into vaccine and placebo groups.

Here are the key results:

  • The mRNA RSV vaccine was 83.7% effective in preventing RSV-associated lower respiratory tract disease with at least two signs or symptoms.
  • The vaccine was 82.4% effective against lower respiratory tract disease with at least three signs or symptoms.
  • Systemic adverse reactions were slightly more common in those who received the vaccine than in the placebo group (47.7% vs 32.9%). Fatigue, headache, myalgia (muscle aches), and arthralgia (joint pain) were the most common in both groups.
  • Serious adverse events occurred in 2.8% of participants in both groups. Most reactions were mild to moderate in severity and were transient. Fewer than 0.1% were reported to be related to the shot.


This new mRNA-based RSV vaccine isn’t exactly groundbreaking since we already have three different RSV vaccines on the market. However, it shows the power of mRNA technology to quickly develop vaccines for infectious diseases (and cancer).

There is a long list of infectious diseases that could be conquered by new vaccines, and it’s clear that mRNA vaccines are leading the way. I’ve already got my RSV vaccination, so I probably will never get this new one, but I would have asked for it if it had been available.

Now, it’s time for the amusing comments from our anti-vaxxer friends.


  • Wilson E, Goswami J, Baqui AH, Doreski PA, Perez-Marc G, Zaman K, Monroy J, Duncan CJA, Ujiie M, Rämet M, Pérez-Breva L, Falsey AR, Walsh EE, Dhar R, Wilson L, Du J, Ghaswalla P, Kapoor A, Lan L, Mehta S, Mithani R, Panozzo CA, Simorellis AK, Kuter BJ, Schödel F, Huang W, Reuter C, Slobod K, Stoszek SK, Shaw CA, Miller JM, Das R, Chen GL; ConquerRSV Study Group. Efficacy and Safety of an mRNA-Based RSV PreF Vaccine in Older Adults. N Engl J Med. 2023 Dec 14;389(24):2233-2244. doi: 10.1056/NEJMoa2307079. PMID: 38091530.
Michael Simpson
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