Pfizer Inc said it has begun testing fully vaccinated adults over 65 in a new study that uses the company's 20-valent pneumococcal conjugate vaccine (20vPnC) candidate with a third dose of the Pfizer-BioNTech Covid-19 shot.

The aim of the study is to understand if the combination of the vaccines is safe, and the immune response after adding the pneumonia vaccine to the existing Covid-19 vaccine, Pfizer said.

Reuters reports that the vaccine candidate, 20vPnC, is being developed to help protect adults against 20 serotypes responsible for the majority of invasive pneumococcal disease and pneumonia.