Haemophilus Influenzae Type b (Hib): The Disease & Vaccine
“Children with Hib came in struggling to breathe. They couldn’t breathe because their epiglottis, a skin flap at the top of the windpipe, was infected, cutting off their airflow. We had a room that was dark, except for an aquarium, and the children were taken there to wait for the “epiglottitis team.” Hospitals had these specialized teams composed of physicians; ear, nose and throat specialists; anesthesiologists; and nurses who were experienced in quickly and efficiently intubating patients. The goal of the epiglottitis team was to keep these patients — often young children less than 5 years old — calm and quickly insert a breathing tube. It was the first step in helping them survive their infection.”
This is the story told by pediatricians who practiced medicine before there was a vaccine against Haemophilus influenzae type b, or Hib. Older pediatricians understand the value of the Hib vaccine because they watched this vaccine, first introduced in the early 1990s, virtually eliminate a disease that affected about 20,000 children every year in the U.S. Today, children receive three or four doses of Hib vaccine between 2 and 15 months of age, and many younger pediatricians have never seen a patient with Hib.
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Get a summary of the information on this page:
The disease
What is Haemophilus influenzae type b?
Haemophilus influenzae type b (Hib) is a bacterium that infects the lining of the brain. An infection in this part of the brain is called meningitis. Meningitis is caused by several different bacteria and some viruses. However, before there was a vaccine, Hib was by far the most common cause of bacterial meningitis in children. Symptoms of Hib meningitis can progress to include coma and death. Some children recover but are left permanently paralyzed, deaf, blind or mentally impaired.
Children under 5 are at the greatest risk for Hib infections. Their symptoms depend on where the infection occurs:
- Lining of the brain, called meningitis – can cause fever, stiff neck and drowsiness
- Bloodstream, called sepsis
- Lungs, called pneumonia
- Lower (deep) layers of skin called cellulitis
- Joints, called arthritis
- Epiglottis (skin flap at top of windpipe), called epiglottitis
One of the more frightening conditions was the last one. The epiglottis prevents food from entering the windpipe when we swallow. When the epiglottis is infected, it becomes inflamed, causing it to block the windpipe. As a result, air cannot pass into the windpipe, causing suffocation and occasionally death.
Find out more about meningitis in this video discussion between two CHOP doctors.
How do you catch Hib?
Hib bacteria commonly line the surface of the nose and the back of the throat. Because most adults are immune to Hib, a mother will passively transfer antibodies from her own blood to the blood of her newborn baby before the baby is born. The antibodies that the baby gets before birth usually last for a few months. However, after that time, the baby is unprotected. Two points are important:
- Most children who first come in contact with Hib don't have a problem. But before the Hib vaccine, about 20,000 children every year in the U.S. would get serious and occasionally fatal infections. Most children harmed by Hib were previously healthy and well nourished.
- The timing of the Hib vaccine during infancy takes into account both the diminishing protection from maternal antibodies as well as the increased risk early in life. This is why the vaccine is started at 2 months of age. By starting the vaccine on time and staying on schedule, most infants will be protected with their own immunity by the time their protection from mom’s antibodies goes away.
The vaccine
How is the Hib vaccine made?
The Hib vaccine is made from the sugar coating of the bacteria. The sugar coating is called a polysaccharide. Antibodies directed against the Hib polysaccharide protect the child against an infection that could result in permanent disabilities or death.
Unfortunately, children less than 2 years old don't develop very good immune responses to polysaccharides, even if exposed to them through infections. For this reason, children less than 2 years old who catch Hib and survive the infection are still recommended to receive Hib vaccine. Scientists have figured out that by taking the Hib polysaccharide and linking it to a harmless protein, young children are able to make a stronger immune response to the polysaccharide. A vaccine that includes a harmless protein attached to a polysaccharide is called a “conjugate” vaccine.
The conjugate Hib vaccine works extremely well. Before the vaccine, Hib caused about 20,000 cases of serious disease in the United States every year. In 2019, 18 cases of Hib in children 5 years of age and younger were reported to the Centers for Disease Control and Prevention (CDC). In 2023, the CDC evaluated cases of Haemophilus influenzae reported in 14 states; these states recorded about one-quarter of the cases of disease throughout the U.S. that year. Of those, 13 cases of Hib occurred in children less than 5 years of age. Most of those children were unvaccinated or had not yet finished their doses of vaccine.
What are the side effects of the Hib vaccine?
After receiving the Hib vaccine, some children may experience:
- Pain or soreness at the injection site
- Low-grade fever
- Loss of appetite
- Irritability
The Hib vaccine does not cause serious side effects.
Other questions you might have
Is the Hib vaccine recommended for anyone other than infants?
Most often the Hib vaccine is given to infants. But, in a few cases other people may be recommended to get this vaccine, such as those:
- Without a spleen or with a spleen that doesn’t work
- Preparing to have their spleen surgically removed
- With sickle cell disease
- Who had a bone marrow transplant (even if they were previously vaccinated against Hib)
- Between 5 and 18 years old who have been diagnosed with HIV
If you are concerned that you or a family member might need this vaccine, talk with your healthcare provider.
Is it true that more than one type of infection can cause meningitis?
Yes. Meningitis refers to an infection that has reached the lining of the brain and spinal cord. It can be caused by viruses or bacteria.
Meningitis caused by a virus, called viral meningitis, is the most common type of meningitis. It is often less severe than bacterial meningitis. Vaccine-preventable diseases that can cause viral meningitis, include measles, mumps, chickenpox and influenza.
Bacterial meningitis tends to be more severe. However, most cases of bacterial meningitis can be prevented by vaccination. The bacteria most often associated with meningitis include meningococcus, pneumococcus, and Hib. Most children are fully immunized against pneumococcus and Hib by 2 years of age, and most adolescents are protected against meningococcus.
Find out more about meningitis in this video, “Doctors Talk: Meningitis.”
Relative risks and benefits
Do the benefits of the Hib vaccine outweigh its risks?
The Hib vaccine has caused a dramatic decline in the incidence of meningitis, bloodstream infections, and pneumonia caused by Hib. However, Hib bacteria still circulate in the community and occasionally cause disease.
On the other hand, the Hib vaccine causes no serious side effects. Therefore, the benefits of the Hib vaccine clearly outweigh its risks.
Disease risks
- Meningitis
- Sepsis
- Epiglottitis
- Arthritis
- Cellulitis
- Pneumonia
- Disease can be fatal
Vaccine risks
- Pain or soreness at the injection site
- Low-grade fever
- Loss of appetite
- Irritability
Reference
Orenstein WA, Offit PA, Edwards KM and Plotkin SA. Haemophilus Influenzae Type b Vaccines in Plotkin's Vaccines, 8th Edition. 2024, 348-364.
Reviewed by Paul A. Offit, MD, on February 25, 2026