Respiratory Syncytial Virus (RSV) is a common respiratory pathogen that causes mild, cold-like symptoms for most people. However, for vulnerable populations such as infants, young children, and older adults, an RSV infection can lead to severe lower respiratory tract diseases, including bronchiolitis and pneumonia. The development and approval of RSV vaccines offer hope for preventing severe illness in these at-risk groups, prompting questions about their scientific approaches.
The Technology in Approved RSV Vaccines
The initial RSV vaccines approved in the United States, Arexvy from GSK and Abrysvo from Pfizer, are not messenger RNA (mRNA) vaccines. These vaccines utilize recombinant subunit protein technology. They target a modified version of the RSV fusion (F) protein, stabilized in its prefusion conformation, which is a primary target for potent neutralizing antibodies crucial for immune protection. Moderna’s mRESVIA, an mRNA-based RSV vaccine, has also received U.S. FDA approval for adults aged 60 and older, and for those aged 18-59 at increased risk.
How Recombinant Subunit Vaccines Work
Recombinant subunit vaccines function by presenting a specific, purified piece of a virus to the immune system. Scientists identify a particular protein from the virus, such as the prefusion F protein of RSV, known to elicit a strong protective immune response. This genetic information is inserted into an organism, like a yeast or insect cell, to produce large quantities of this viral protein. Once produced, the protein is extracted and purified. An adjuvant, a substance that helps enhance the immune response, is often added to these purified proteins.
When administered, the immune system encounters this isolated viral protein and learns to recognize it as foreign. This prompts the body to generate specific antibodies and memory cells against the protein. This is similar to showing the immune system a “mugshot” of the virus’s most recognizable feature, allowing it to prepare its defenses without exposure to the actual infectious agent. This method ensures the vaccine contains no live virus or viral genetic material capable of replication.
mRNA Vaccines as a Comparison
Messenger RNA (mRNA) vaccines operate on a different principle, providing the body with instructions rather than a direct viral component. Instead of injecting a viral protein, mRNA vaccines deliver a synthetic strand of mRNA into human cells. This mRNA carries the genetic blueprint for a specific viral protein, such as the spike protein found on the surface of viruses like SARS-CoV-2.
These mRNA molecules are encased within lipid nanoparticles, which help them enter the body’s cells. Once inside the cytoplasm, cellular machinery, known as ribosomes, reads these instructions and begins producing the designated viral protein. The immune system then identifies these newly made proteins as foreign, triggering the production of antibodies and specialized immune cells. The mRNA itself is transient; it does not enter the cell’s nucleus, where DNA is stored, and it naturally breaks down within a few days after delivering its message. This approach teaches the body to create its own “mugshot” for the immune system to learn from.
Future Developments in RSV Vaccine Technology
While recombinant subunit and mRNA-based RSV vaccines are currently available, scientific research continues to explore other vaccine technologies. Researchers are investigating different platforms, including live-attenuated vaccines, which use a weakened form of the virus, and viral vector vaccines, which employ a harmless virus to deliver genetic material. This aims to achieve varying immune responses, potentially broader protection, or improved manufacturing scalability.
Scientists are also developing combination vaccines that could protect against RSV alongside other respiratory pathogens, such as human metapneumovirus (hMPV). This ongoing research aims to optimize vaccine efficacy, extend protection to a wider range of age groups, and streamline vaccine administration. The continuous pursuit of diverse technologies ensures a robust pipeline of preventive strategies against RSV and other infectious diseases.