Haemophilus influenzae type b (Hib)

What is this disease?

Haemophilus influenzae is a bacteria. There are several types (a-f) and many untypable varieties. These bacteria have been found in the microbiome of humans. They can be benign or cause infection. Infection occurs almost exclusively in children under the age of 5 (85% of infections). It is a spread from respiratory tracts of infected people coughing or sneezing near susceptible people which then breathe in the bacteria. The bacteria does not survive in the environment. Peaks of the disease are September-December and again in March-May.

Infections include mild ear infections right up to serious infections called ‘invasive infections’. The most common non-invasive infections are ear infections and bronchitis.

An invasive infection is one that is in an area that is in an area where bacteria should not exist in your body such as your bloodstream, pleura (space around your lungs), or spinal cord. The most common invasive infections for Haemophilus influenzae are: pneumonia (lung; only invasive if infecting pleura or blood), bacteremia (blood), meningitis (brain & spinal cord), epiglotitis (throat), cellulitis (skin), and infectious arthritis (joint). Symptoms of the disease vary by organ that is infected. All will typically include fever.

Recurrent infections can occur in those under the age of 2. Those over 2 who have been exposed to Hib will likely develop immunity.

Morbidity & Mortality Stats

Fatal cases of Hib infection are at 3-6% in the United States. In 2015, the CDC estimates that the US had 1,600 cases of invasive infection in children under 5 years. In 2015, 1,015 deaths were attributed to Hib in children under the age of 5. Of note, these statistics are much better than the 2020 goal. Non-b and nontypable cases and deaths were higher than type-b in 2015. There were 23.9 million children in the US under the age of 5 in 2015.

Pre-vaccine incidence of Hib meningitis under the age of 5 in the majority of the US was approximately 50-60/100,000 per year, except in the southwest closer to 90/100,000 and in Alaska over 100/100,000. Pre-vaccination northern Canada, Alaska, and northern and central Australia had some of the highest rates worldwide. Pre-vaccination there was a 5% case fatality rate. Before vaccination (stats from 1985), it was estimated that there were 20,000 cases of invasive HIB infections in children 5 years and younger annually in the US. The U.S. population from 0-5 years in 1985 was 21.4 million children. Two-thirds of those children with invasive infections were meningitis cases. 15-30% of those meningitis cases had permanent effects from the infection and 4% of the cases were fatal. Other causes of bacterial meningitis in this age group include Group B Streptococcus, Streptococcus pneumoniae, Listeria monocytogenes, Escherichia coli, and Neisseria meningitidis. Vaccinations began in 1986 in the US. Vaccines at that time was a version known as the PRP which was shown in a trial in the 70s to have no efficacy in kids under 18 months.

Conjugate vaccines (which is used today) started in 1991. The conjugate vaccine job is to prevent nasopharyngeal Hib colonization. Before these vaccines, Hib could be isolated in 0.5-3.0% of all infants and children. Pre-conjugate vaccination it is estimated that there were 88 cases/100,000 children under 5 per year. Post-conjugate vaccination 1.6 cases/100,000 children under 5 per year.

How do you treat this disease?

Diagnosis is accomplished by testing the appropriate body fluid. It is treated with antibiotics, typically a 7-10 day course. Non-invasive cases may not require antibiotic treatment. Invasive infections are treated with antibiotics and typically require hospitalisation. Invasive infections can result in serious complications such as loss of limbs with blood infections and with meningitis loss of hearing and brain damage, even as severe as death. Successful treatment of meningitis leaves approximately 30% of children with some sort of permanent challenge, usually hearing loss.

Because fever is the only sign that is common in all of the invasive infections, here is a good review on how to manage fever. Most of the time fever (body temperature over 100.4 degrees Fahrenheit) is a healthy response that shows your child’s immune system is working properly to fight infection. Rectal thermometers are the best kind. Use these in smaller children. Use oral thermometers in older kids if rectal is not tolerated after they have not had anything to eat/drink for a while. Seek care if any of the following apply to your child:

• Your child’s behavior changes dramatically, they have no interest in usual things such as food and play. In a baby they cry excessively and cannot be soothed.
• Baby under 3 months rectal temperature is over 100.4 degrees Fahrenheit
• Baby under 2 years with a fever lasting more than 24 hours
• Child is over 2 and the fever lasts more than 3 days
• Child of any age repeatedly spikes over 100.4 degrees Fahrenheit

Treat fevers in children at home with hydration, taking off their clothes/blankets, & giving them lukewarm baths. If any of the above apply, please call your healthcare provider.

How do you prevent meningitis infection?

The CDC recommends prevention by avoiding cigarette smoke, getting plenty of rest, and avoiding close contact with sick people in addition to the vaccination according to their standard schedule. They state on their site that the healthy lifestyle factors are especially important for young children, the elderly, those with weak immune systems, and those without a functioning spleen.

How do you prevent Hib invasive infections?

Current thinking is that a respiratory infection from a virus or a mycoplasma preceding the Hib infection may predispose a child to an invasive infection.

Breastfeeding is protective.

Pre-vaccination most children acquired immunity by age 5-6 from an asymptomatic infection of Hib.

How effective is this vaccine?

Since vaccination has been standard with the conjugate vaccine cases have dropped 99%. Clinical efficacy is stated to be 95-100%.

However, 36% of confirmed cases of invasive Hib infection in children aged 6 months-5 years, the child is fully vaccinated. The cause for this is unknown.

Side-effects and adverse events from of vaccine

Redness & swelling

Shoulder injury

Vasovagal syncope (fainting)

To date (6/26/17) 41 injury cases and 3 death cases have been filed with VAERS.

As always, before administering this or any vaccine to your child, please read the current insert of the particular version your child will be receiving. This can be obtained from the healthcare provider or the internet, different versions of the vaccine may be more appropriate for your child than others.

Different versions of this vaccine

PRP-T versions require 3 doses at 2, 4, and 6 months. These include: ActHIB, Pentacel, Hiberix, & MenHibrix

PRP-OMP versions require only 2 doses at 2 & 4 months. These include: PedvaxHIB & COMVAX.

Hib vaccines should never be given to a child under 6 weeks, a child who is currently ill, or a child who has had a reaction to a previous injection of Hib vaccine.

Boosters are also given at 12-15 months.

Alternative Schedules

Canadian schedule is 4 doses at 2, 4, 6, and 18 months.

In Europe 2-3 doses are given.

Alternative schedule A) 2,4,6,& 12 months with the ActHIB version recommended

Alternative schedule B) Aluminum-free version recommended at 3, 5, 7, & 15 months.

References:

• CDC Website
• Heikki Peltola. 2000. Worldwide Haemophilus influenzae Type b Disease at the Beginning of the 21st Century: Global Analysis of the Disease Burden 25 Years after the Use of the Polysaccharide Vaccine and a Decade after the Advent of Conjugates. Clin Microbiol Rev. 2000 Apr; 13(2): 302–317.
• Hopkinsmedicine.org
• Immunize.org
• Pediatrician Websites for alternative schedule information.
• Vaccine Injury Compensation data, accessed 6/26/17.
• WHO website