The panel that advises the Centers for Disease Control and Prevention is recommending adults 65 and over receive Pfizer’s pneumococcal vaccine Prevnar 13 as a routine healthcare measure.

The CDC still has to give its OK, but the recommendation includes providing the vaccine even for adults who have already received Merck’s Pneumovax 23.

Pfizer has been talking up the possibility of this endorsement for a while, but Leerink analyst Seamus Fernandez wrote in his Wednesday research note that the financial bounce—estimated to be around $2 billion in peak additional revenue—could be limited: the Advisory Committee on Immunization Practices (ACIP) also noted in its endorsement that it will reassess its position in 2018. If all is good, herd immunity might take hold, which means the vaccine is doing just what it should, but that could also mean fewer patients who will need to be treated.

The financial impact also depends on whether or not the Centers for Medicare and Medicaid Services signs off on the deal—if CMS agrees to cover the treatment, money flows towards Pfizer, but Fernandez noted that CMS currently covers just one vaccine dose. This means that patients who have already received Pneumovax would not be covered.

Fernandez added that CMS probably won’t be able to enact a new vaccine policy until 2016, so Pfizer may have to wait before it can reach the full 65-and-older set. Although anticipating a delayed burn for Pfizer, Fernandez wrote that a CDC endorsement could have an immediate impact on Merck’s Pneumovax, because it would give the 15 million unvaccinated Medicare/Medicaid a second choice.

Fernandez writes that advocates told ACIP even vaccinating 10% of the eligible population in the upcoming respiratory illness season could prevent 5,000 cases of community-acquired pneumonia.