Dive Insight:

RSV has eluded vaccine makers for decades but could have several preventive shots relatively soon, if current studies prove positive. Pfizer, J&J and GSK all expect to deliver data from Phase 3 trials in older adults later this year, which could allow them to reach a market expected to be worth $10 billion by 2028.

(Last week, however, GSK announced it was pausing trials of one formulation of its RSV vaccine in pregnant women over safety concerns, a decision that didn’t affect its study in older adults.)

Moderna now figures to be a competitor, too. MRNA-1345 began mid-stage safety and efficacy testing in November, and the trial’s independent data and safety monitoring board has cleared it at the dose selected for a pivotal trial.

Even though the Massachusetts-based biotech is behind the bigger drugmakers in getting its Phase 3 program under way, it may have some opportunities to catch up. RSV is normally a virus that circulates in the winter, meaning Moderna has largely missed the Northern Hemisphere season. However, the company noted that the Centers for Disease Control and Prevention detected more out-of-season infections in 2021, something other countries have also seen.

Moreover, manufacturing of mRNA vaccines is simpler than the protein-based shots being developed by GSK and Pfizer, potentially allowing Moderna to scale up more quickly. The relative simplicity of mRNA vaccines was shown by the quick development and production of COVID-19 vaccines from Moderna and Pfizer.

RSV has proven to be a difficult disease to prevent with vaccines, however. Experimental shots developed in the 1960s stimulated antibodies that didn’t neutralize the virus and produced an immune response in some that can make the disease worse.

The current burst of development has been aided by a better understanding of how to target RSV’s F protein. That protein changes shape as it enters human cells, and neutralizing antibodies are more potent when they bind to the F protein beforehand.