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The Hib Vaccine

[Note: AAP = American Academy of Pediatrics; CDC = Centers for Disease Control; VAERS = Vaccine Adverse Event Reporting System]

Basic Hib Facts

From the CDC's Vaccine Information Sheet:

• Hib is the bacterial disease caused by Haemophilus Influenzae type B.
• Usually strikes children under 5 years old.
• Before the vaccine, was the leading cause of bacterial meningitis in children under the age of 5
• Before the vaccine, approximately 20,000 cases, 1,000 deaths, per year in the USA

The Pro-vaccination view

The AAP's Guidelines for Parents brochure has some basic facts:

• "Before the vaccine was used, H influenzae type b was the most common cause of bacterial meningitis in the United States. It caused about 12,000 cases of meningitis each year in children younger than 5 years of age–especially in babies 6 to 12 months old. Of those children infected, 1 in 20 died from this disease, and 1 in 4 developed permanent brain damage."

The AAP recommended vaccination schedule:

• Vaccinations are reccomended for Hib at 2, 4, 6 (sometimes) and 12-15 months.
• "Three Haemophilus influenzae type b (Hib) conjugate vaccines are licensed for infant use. If PRP-OMP (PedvaxHIB or ComVax [Merck]) is administered at 2 and 4 months of age, a dose at 6 months is not required. Because clinical studies in infants have demonstrated that using some combination products may induce a lower immune response to the Hib vaccine component, DTaP/Hib combination products should not be used for primary immunization in infants at 2, 4, or 6 months of age unless FDA-approved for these ages."

BabyCenter provides some additional facts (no attribution):

• "It's especially important that your child receive this vaccine on schedule because the diseases it protects against tend to strike children between the ages of 2 months and 2 years. The protective immunity your child receives from the Hib vaccine is more complete than it would be if she got the disease itself."
• "Up to a quarter of children have some redness, warmth, or swelling at the site of the injection. One in 20 children has a fever of 101 degrees F (38.3 Celsius) or higher. These symptoms may show up within a day of vaccination and can last two to three days. The Hib vaccine in use today has never been known to cause any serious reactions, and most children have no side effects at all after getting it."

Some more information from the web site of the Bill & Melinda Gates Children's Vaccine Program:

• "Most serious Hib disease occurs in children between six and twelve months of age."
• "Before Hib vaccine virtually eliminated this disease in the United States, 1 of every 200 children in the United States was made ill by the disease."

Hib is on the list of "notifiable diseases" that the Federal government keeps track of. In 1998 (the most recent year for which the report is available) there were 255 reported cases, according to the CDC:

"In 1998, a total of 255 cases of Haemophilus influenzae (Hi) invasive disease among children aged less than 5 years were reported (data were provided by the National Immunization Program and were based on date of onset, not MMWR week). Before a vaccine was introduced in 1987, approximately 20,000 cases of H. influenzae type b (Hib) invasive disease occurred among children annually (JAMA 1993;269:221-6). The sharp decline in the number of Hib cases is attributed to the widespread use of the Hib vaccine among preschool-aged children. Of the 255 cases reported in 1998, a total of 197 (74%) Hi isolates were serotyped, and 61 (31%) of these were type b. Among the 61 cases of Hib invasive disease reported in children aged less than 5 years, 25 (41%) were among children aged less than 6 months, which is too young to have completed a three-dose primary Hib vaccination. However, 22 (61%) of the 36 children who were old enough (i.e., aged greater than or equal to 6 months) to have completed a three-dose primary series were incompletely vaccinated or their vaccination status was unknown. These cases might have been prevented with age-appropriate vaccination."

Mercury in Hib Vaccine

There is some concern, which the AAP shares, that the Hib vaccine is one of the vaccines using thimerosal, an organic mercury compound, as an antibacterial preservative. Given the known dangers of organic mercury compounds, the AAP is urging manufacturers to work towards eliminating this compound. You can read their recommendations here.

According to an article from Clinician Reviews, thimerosal has largely been eliminated from Hib vaccines:

"Three of the four US-licensed vaccines for Haemophilus influenzae type b (Hib) do not contain the preservative. The fourth, manufactured by Wyeth Lederle, is available in both single-dose (thimerosal-free) and multidose (thimerosal-containing) formulations; as of July 2000, the company is scheduled to produce only the single-dose, thimerosal-free Hib formulation for use in the United States. The combination hepatitis B/Hib vaccine produced by Merck has always been free of the preservative."

From the Product Insert

As a parent, you have the right to see the product insert from any vaccine that's going to be given to your child. Be prepared for a lot of very tiny print. We have the product insert for Pasteur Merieux Connaught's ActHIB vaccine, the brand that our physician administers.

One interesting table shows the effectiveness of the vaccine in provoking an antibody response. In a variety of studies, this particular vaccine led to antibody levels greater than 1 microgram per ml in between 83% and 96% of those given the vaccine. Some other brands did not fare as well, notably PedvaxHIB which ran as low as 50% in one study.

They also have a table of side effects. Of note for the 2-month vaccination:

• Tenderness 46.3%
• Erythema  (redness) 14.3%
• Induration (hard spot) 22.5%
• Fever over 100.8 F 20.1%
• Irritability 72.6%
• Drowsiness 57.5%
• Anorexia 15.3%
• Diarrhea 4.4%
• Vomiting 2.7%
• Persistent Crying 1.6%

But, because Hib is generally given at the same time as DTaP, it's comforting to note "In general, the rates of minor systemic reactions about ActHIB and DTP immunization were comparable t those usually reported after DTP vaccine alone."

The insert also discusses major adverse reactions: "In a randomized, double-blind US clinical trial, ActHIB was given concomitantly with DTP to more than 5,000 infants and hepatitis B vaccine was given with DTP to a similar number. In this large study, deaths due to sudden infant death syndrome (SIDS) and othe causes were observed but were not different in the two groups. In the first 48 hours following immunization, two definite and three possible seizures were observed after ActHIB and DTP in comparison with none after hepatitis B vaccine and DTP. This rate of seizure following ActHIB and DTP was not greater than previously reported in infants receiving DTP alone. Other adverse reactions reported with administration of other Haemophilus b conjugate vaccines include urticaria, seizures, hives, renal failure, and Guillain-Barre syndrome (GBS). A cause and effect relationship among any of these events and the vaccination has not been established."

The Anti-Vaccination View

The National Vaccine Information Center is probably the largest anti-vaccination group around. There does not appear to be any information, pro or con, about the Hib vaccine on their web site.

VaccineWebsite.com collects a wide variety of somewhat disorganized information about Hib. They raise some concerns about possible associations with asthma and diabetes. They also indicate that the vaccine may actually cause Hib disease in some cases. This site does not strike me as a balanced attempt at presenting the medical literature, but it's worth a quick look.

Randall Neustaedter's The Vaccine Guide: Making an Informed Choice (see my review) suggests that studies of the vaccine's efficacy are flawed (though he does not offer an alternative explanation for the sharp decline in Hib cases) and passes on reports of Guillain-Barre Syndrome, transverse myelitis, seizures, and thrombocytopenia (a bleeding disorder). His summary:

1. Hib meningitis is a potentially life-threatening disease, and long-term sequelae of infections (hearing loss, learning disabilities) do occur.
2. Long-term effectiveness of the vaccines has not been determined, and reports of short-term effectiveness vary considerably.
3. Serious vaccine-associated reactions have been reported.
4. The vaccine has been associated with an increased susceptibility to Hib meningitis in the first week following vaccination.

Adverse Reactions Defined

• Urticaria - The technical term for hives.
• Renal Failure - Impaired function of the kidneys
• Guillain-Barre syndrome (GBS) - A degenerative nervous disorder that leads to weakness and paralysis
• Transverse myelitis - A degenerative disease of the spinal cord
• Thrombocytopenia - A decrease in the number of platelets (cells that help clotting) in the blood

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