Despite a fast-tracked FDA approval, the Centers for Disease Control is holding off on endorsing pneumonia vaccine Prevnar 13 for adults 50 and over pending results of a study not due to wind down until next year.

The CDC already endorses the Pfizer drug for children, but said Wednesday it wants to see the results of a study being conducted in the Netherlands before backing the drug’s use among a broader population. Results on that study are expected next year. FDA approved the vaccine for use in adults 50 and over in December.

The CDC’s advisory council currently endorses Merck’s Pneumovax for adults who are at least 65, and it is approved for the over-50 set. Pfizer’s Prevnar 13 protects against 13 serotypes, one of which is not covered by Merck’s Pneumovax.

Although the 84,000-person study the CDC is waiting on won’t be finished until next year, Pfizer isn’t holding back. It said in a statement that it will go ahead with its plans to market Prevnar 13 as an adult vaccine over the next few weeks. The company said it does not expect the CDC’s reservations to affect its sales outlook.

CDC data estimates that pneumococcal pneumonia kills about 5% to 7% of infected patients, with a higher percentage among the elderly, and the FDA estimates the disease hospitalizes 300,000 adults in the 50-plus age range every year.