Respiratory Syncytial Virus (RSV) is a common respiratory pathogen that can cause significant illness, especially in vulnerable populations. While many people associate RSV with mild, cold-like symptoms, it can lead to severe infections of the lungs and breathing passages, such as bronchiolitis and pneumonia. For individuals at higher risk, these infections can necessitate hospitalization and even become life-threatening. While several approved RSV vaccines are protein-based, Moderna’s Mresvia is an mRNA vaccine, approved in May 2024.
The RSV Vaccine: A Protein-Based Approach
Most RSV vaccines use a protein-based subunit approach. These vaccines introduce specific, purified components of the virus to the immune system. GSK’s Arexvy and Pfizer’s Abrysvo are two prominent protein-based RSV vaccines. Both Arexvy and Abrysvo target the prefusion F protein, a surface protein on the RSV virus. This F protein form is a primary target for neutralizing antibodies, making it an effective vaccine component.
Arexvy is approved for individuals 60 years and older, and also for adults 50 through 59 years at increased risk for lower respiratory tract disease caused by RSV. Abrysvo is approved for adults 60 years and older, adults 18 through 59 years at increased risk, and pregnant individuals at 32 through 36 weeks gestational age to protect their infants from birth through six months of age.
How Protein-Based Vaccines Work
Protein-based vaccines function by presenting specific, purified viral proteins, known as antigens, directly to the immune system. These antigens are carefully selected parts of the virus that are known to provoke a strong immune response. The immune system recognizes these introduced proteins as foreign.
Upon recognition, the body initiates an immune response by producing antibodies and activating specialized T-cells. These antibodies can then bind to the viral proteins, blocking the virus from infecting cells if a person is later exposed to RSV. This process allows the body to develop immunity without being exposed to the whole, live virus, thereby preventing illness. Adjuvants, substances that enhance the immune response, are sometimes included in these vaccines to ensure a robust and lasting protective reaction.
What Makes mRNA Vaccines Different?
mRNA vaccines operate differently than protein-based vaccines. Instead of introducing viral proteins directly, mRNA vaccines deliver genetic instructions to the body’s cells. These instructions, in the form of mRNA, teach the cells how to produce a specific viral protein, such as the RSV F protein.
Once the cells produce the viral protein, the immune system recognizes it as foreign and mounts an immune response, generating antibodies and T-cells. The mRNA itself does not alter human DNA and is quickly broken down by the body’s cellular machinery after delivering its instructions. Moderna’s Mresvia, an mRNA RSV vaccine approved in May 2024, exemplifies this technology, providing an alternative vaccination strategy for adults.
Who Should Consider the RSV Vaccine?
RSV vaccination is recommended for specific populations who face a higher risk of severe illness. Adults aged 60 years and older are advised to consider RSV vaccination due to waning natural immunity with age. Individuals aged 50 through 74 years with increased risk factors for severe RSV disease, such as chronic heart or lung conditions or a weakened immune system, are also recommended to receive the vaccine. Pregnant individuals, specifically between 32 and 36 weeks of gestation, can receive an RSV vaccine (Abrysvo) to transfer protective antibodies to their developing babies. This maternal vaccination provides passive immunity, shielding infants from severe RSV during their most vulnerable first six months of life.