Parents are being warned "not to gamble" with children's lives by charity Meningitis Now, as research suggests a slight decline in the number of babies receiving vaccinations.
While over 92 per cent received the first Meningitis B vaccine given between eight and 16 weeks old, this number drops four per cent by the time they receive a booster at age one.
As many as 100,000 toddlers are being put at a possible increased risk of the disease, Meningitis Now warns.
“This drop off rate is significant and very worrying, particularly given that this is a new vaccine and we don’t yet know how long protection will last," said Dr Tom Nutt.
"Like other parents, I appreciate that life can easily get in the way and that routine vaccines can sometimes seem less than a priority or be easily forgotten."
Meningitis is an infection of the lining around the brain and spinal cord, and is usually caused by bacteria or viruses.
Meningitis B most commonly affects babies and young children, with symptoms including fever, vomiting, drowsiness and a rash.
Meningococcal infections tend to come in bursts, the charity says.
In the past 20 years, between 500 and 1,700 people every year, mainly babies and young children, have developed MenB disease, with around one in 10 dying from the infection.