Vaccination is a key strategy for preventing respiratory illnesses. Pneumococcal vaccination is recommended for all adults aged over 60 or 65 years (depending local guidelines) who have never received a pneumococcal vaccine or whose previous vaccination history is unknown. Given their wide application, co-administration of pneumococcal and Covid-19 vaccines may support broad population-wide coverage. However, it is unclear whether the co-administration of the Novavax (NVX) vaccine and a 20-valent pneumococcal conjugate vaccine (PCV20) results in lower immunogenicity than the administration of either alone.

The investigators will thus conduct a 4-four arm study with the following treatments: NVX plus placebo (NVX arm), PCV20 plus placebo group (PCV20 arm), NVX plus PCV20 (Combination arm), and placebo plus placebo group (Placebo arm). Vaccines and/or placebo will be administered as single doses, given as intramuscular injections on Day 1 (one in each shoulder). Subjects will be randomly assigned to one of the four arms.

The outcome will be the antibody levels after 28 days.

Inclusion Criteria:

• Age: 60 years or older
• Males and females
• Able and willing (in the investigator's opinion) to comply with all study requirements.
• Participants, who already received three Covid-19 vaccines, of which the third was a mRNA vaccine (BNT162b2 or mRNA-1273) and at least 16 weeks ago
• Only applicable for women: last menstrual bleeding more than one year ago

Exclusion Criteria:

• Use of immunosuppressants
• Congenital or acquired immunodeficiency (eg, history of HIV infection, hematological disease, current malignancy, or others)
• Chronic condition that may significantly interfere with the immune response in the opinion of the investigator
• History of Covid-19 within 16 weeks before study vaccination
• Previous pneumococcal vaccination
• Contraindication against any ingredient of the NVX or the PCV20 vaccine