Carriage to Assess Protection of New Pneumococcal Vaccines - PCV15

Streptococcus pneumoniae (pneumococcus) is a bacterium that causes just under four million serious infections every year. It is normal for pneumococcus bacteria to live in the noses of healthy adults and children as part of the nasal microflora without causing harm. This is called "carriage". But the bacteria can still be passed on to other people. If they are at-risk, for example elderly, or very young, or have pre-existing health conditions, the pneumococcus bacteria can cause pneumonia, which can cause serious life-threatening illness.

Pneumococcus bacteria are surrounded by a sugar capsule. But the capsule does not always have the same components. As a result, the bacteria are classified into more than 100 different types. To make them effective, the vaccines that are currently available contain the sugar capsules of the most common pneumococcal types that cause disease.

One such vaccine - PCV13 - has been effective globally in protecting against pneumococcus disease. It works because it controls the "carriage" (how a person carries the bacteria in their nose) of 13 types of the bacteria. Vaccines giving protection against other types of the bacteria are also becoming available worldwide. PCV15 is similar to PCV13 and protects against two additional types of the bacteria so may offer more protection.

This study, which lasts 2 months and is funded by Merck Sharp \& Dohme (MSD), aims to assess if using PCV15 can protect against "carriage". To do this, investigators will use a well-established method already used with more than 2,000 people safely in other research. This involves "challenging" volunteers by putting a small amount of the pneumococcus bacteria into their noses. In this study, before they are challenged, volunteers will either be vaccinated with the real PCV15 vaccine or a dummy ("placebo"). The Investigators will then be able to compare the two groups to find out who the vaccine protected and who it did not.

After the study everyone who takes part and fit into certain criteria will be given antibiotics to clear the pneumococcus colonisation. They will also be regularly monitored during the study to ensure their safety.

A very small number of volunteers will be asked to have a biopsy to collect tissue samples from inside their nose before and after being vaccinated with PCV15. This will help researchers to understand more about how the immune system responds to the vaccine.

The information gain in this project will help the investigators to understand how exactly PCV15 vaccine protects people against pneumococcus. This means that this vaccine and future pneumococcal vaccines will be improved to protect many lives in future around the world.