Pfizer on Monday announced a study to explore coadministration of its pneumococcal vaccine along with a third dose of the Pfizer-BioNTech Covid-19 vaccine in older adults.

Pfizer, in a statement, announced that "the first enrolled subjects have received their immunisations as part of a new study in adults ages 65 or older exploring the coadministration of the company's 20-valent pneumococcal conjugate vaccine (20vPnC) candidate following a booster dose of the Pfizer-BioNTech Covid-19 vaccine, currently authorised by the Food and Drug Administration (FDA) under an emergency use authorisation (EUA)".

The trial aims to describe safety when both vaccines are co-administered, with follow-up six months after vaccination and to describe immune responses produced by each of the vaccines.

The trial will include 600 adults who will be recruited from the pivotal Phase 3 Pfizer-BioNTech Covid-19 vaccine trial and will have received their second dose of the vaccine at least six months prior to entering the coadministration study.

The participants will be randomised to one of three groups: 20vPnC plus Pfizer-BioNTech Covid-19 vaccine booster; 20vPnC plus placebo; and Pfizer-BioNTech Covid-19 vaccine booster plus placebo.

Boosters and new versions of vaccines that target the Covid variants are already being explored by both Pfizer and Moderna.

Pfizer CEO Albert Bourla had announced that Covid vaccine recipients will "likely" need a third dose between six to 12 months after they're fully vaccinated. The company is now testing a third booster shot of its vaccine on fully vaccinated people.

US pharmaceutical Moderna in its Phase 2 study found that a third booster shot of its Covid vaccine can rapidly increase the level of antibodies in previously inoculated people.

The 20vPnC candidate vaccine is in development for the prevention of invasive disease and pneumonia caused by 20 serotypes of Streptococcus pneumoniae in the vaccine in adults ages 18 years and older.