But these proteins aren’t just unique to MenB. They may also be found on the surfaces of other types of meningococcal bacteria. This is critical to the vaccines ability to offer some protection against other meningococcal strains.
Uncovering this effect has however been challenging, as just a few weeks before implementing an infant MenB programme, the UK also introduced a MenACWY vaccine for teenagers following a steep rise in cases of a new deadly strain of MenW
. Therefore, it was difficult to measure the impact of the MenB vaccine on MenW disease.
Due to being made differently, there are variations in how these two vaccines work. For example, so far, Bexsero® has only been proven to directly protect vaccinated individuals
, whereas MenACWY vaccines also have indirect effects by stopping the bacteria from being carried in the back of the nose and throat and so reducing the spread. By vaccinating teenagers, the group most likely to carry and unknowingly pass the bacteria on, the chain of transmission is broken: protecting the wider population in an effect known as ‘herd’ or ‘population protection.’
Researchers at Public Health England recently undertook the difficult task of distinguishing the direct effects from the MenB vaccine on MenW disease, on top of any indirect impact offered by the teenage MenACWY programme.
Their work revealed that in the four years since its introduction, Bexsero®
has directly prevented 98 MenW cases in children under five, while the teenage MenACWY programme
has prevented in the region of 114 to 899 cases, depending on which scenario was used in the model. If it was assumed that MenW cases would level off over time, the MenACWY vaccine was estimated to prevent fewer cases, while vaccine impact was greater if it was assumed that cases would continue to increase at the same exponential rate as they were before the vaccine was introduced.