This is the short version. For the long version with references, click here.
What are the “meningitis vaccines”?
There are two basic types of meningitis: viral and bacterial. There are no vaccines targeting viral meningitis. There are three vaccines targeting causes of bacterial meningitis: HiB, pneumococcal, and meningococcal. Meningococcal was Weekly Topic 03, HiB will be discussed here, and pneumococcal will be discussed in a future Weekly Topic.
The HiB vaccine is generally given at 2, 4, 6, and 12-18 months (though it varies by country and province).
What is HiB?
Haemohpilus influenzae type B (HiB) is a bacterium that normally lives in the respiratory tracts of healthy people without causing disease. Up to 5% of the population is infected at a given time, and most children become infected by H. influenzae bacteria by the age of 5, whereby they become immune. Infection is more common in crowded housing and settings such as daycare; in fact, in daycare, the infection rate is approximately 15%. Asymptomatic carriers remain infected and contagious for months at a time and the bacteria easily pass through a long line of asymptomatic carriers before causing disease in someone. It is present in the nose and throat and thus is passed by coughing or contact with mucus.
Because (a) H. influenzae bacteria are a normal part of our respiratory tracts, (b) 100% of the population becomes infected at some point, and (c) most infections are asymptomatic, HiB disease is relatively very rare. However, when it does occur, HiB disease may result in sepsis, meningitis, and even death. Among those with HiB disease, approximately 3-6% die and 15-35% suffer permanent neurological sequelae (the most common being partial hearing loss). The most common symptoms of HiB disease include fever, decreased mental status, and stiff neck.
How can I prevent or treat HiB in my child?
Conditions that make an individual more susceptible to HiB disease include recent viral infection, smoking or other respiratory irritants, immune suppression, and crowded housing or crowded environment. Avoid exposing your child to these triggers as much as possible by smoking cessation, avoiding crowded living spaces if possible, boosting the immune system, etc., and engaging in a generally healthy lifestyle. If your child has a known exposure to HiB, prompt evaluation by a physician for prophylactic antibiotics may be prudent.
Breastfeeding offers significant protection against HiB, lasting several years after weaning. If breastfeeding is not possible due to adoption or other issues, look into relactation, pumping, or donor milk.
How effective are the vaccines at preventing asymptomatic carriage?
HiB carriage is reduced but not eliminated by vaccination. Extremely high vaccination rates reduce but do not eliminate HiB disease. As mentioned above, the bacteria can jump from asymptomatic carrier to asymptomatic carrier regardless of the carrier’s vaccine status before causing disease in a susceptible individual. Therefore, because the vaccine does not prevent asymptomatic carriage, it cannot be relied upon for herd immunity.
How effective is the HiB vaccine?
Prior to the introduction of the vaccine, HiB caused over 80% of all invasive H. influenzae disease among children. The incidence of HiB began to drop before the introduction of the vaccine and continued to drop after the introduction of the vaccine.
The HiB vaccine’s efficacy ranges from -69% (increased risk) to 88% (decreased risk), with the efficacy seeming to depend not only on the type of HiB vaccine used, but also on the populations in which it was used. It varies drastically even from state to state or province to province in the same country.
HiB vaccination is associated with *decreased* type B H. influenzae (HiB) disease and death but *increased* non-B H. influenzae disease and death. The overall net effect of HiB vaccination has been **a net increase in H. influenzae disease and death**. This is likely due to the crippling effect of “original antigenic sin,” where the body is trained to produce antibodies against one strain and becomes unable to produce antibodies against different strains. This makes the vaccinated person at **increased risk of contracting other strains**. Furthermore, the greatest increase in H. influenzae disease and death was in the (unvaccinated) elderly. If herd immunity existed with this vaccine, we would expect a decreased risk in the unvaccinated. However, HiB vaccination of infants was followed by an increased risk in all age groups (vaccinated or unvaccinated) but especially in the (unvaccinated) elderly, suggesting a negative herd effect.
Are there other infectious diseases related to HiB vaccination?
It appears that pertussis vaccination caused an increase in (more dangerous, less treatable) HiB, hence the HiB vaccine; HiB vaccination caused an increase in pneumococcal (even more dangerous, less treatable) infections, hence the PCV vaccine; and the PCV caused an increased in (still more dangerous, less treatable) meningococcal infections, hence the MCV vaccine. There is concern that the MCV will also be followed by the sudden increase of another more dangerous and less treatable bacterial disease.
What are the risks of the vaccine?
Type 1 Diabetes. The HiB vaccine increases the risk of type 1 diabetes with just one dose, and the risk increases with more doses. In fact, the long-term complications from HiB-vaccine-induced type 1 diabetes alone outweigh the long-term complications from HiB disease if no children were vaccinated against HiB.
H. influenzae non-B Invasive Disease. As discussed above, the vaccine is associated with an overall increased incidence in H. influenzae infections and deaths. This is because the increase in non-B infections is more than the decrease in type B infections. The increase in non-B H. influenzae disease and death alone outweighs the drop in type B disease and death.
HiB Invasive Disease. HiB vaccination increases the risk of HiB invasive disease and death in the first week after vaccinating. This has happened as shortly as 3 hours after vaccinating and after a second vaccine when there was no reaction to the first.
Others. Other known or suspected reactions include transverse myelitis, Guillain-Barre Syndrome, thrombocytopenia, SIDS, asthma and allergies, epiglottitis, autism, encephalitis, convulsions (seizures), and allergic reactions to the vaccine (including anaphylaxis).
So what’s the bottom line?
The bottom line is that HiB is so common that 100% of the population carries it at some point and virtually 100% of the population is immune to it by age 5. The vaccine does not prevent asymptomatic carriage and so cannot be relied upon for herd immunity. The vaccine simultaneously decreases the risk of H. influenzae type B, which makes up a minority of strains today, and increases the risk of all other H. influenzae strains. Vaccination of children is associated with an overall increased risk of H. influenzae invasive disease and death in both children and adults, especially the elderly. HiB vaccination is also associated with increased incidence of other more dangerous and less treatable bacterial infections. The vaccine is associated with type 1 diabetes, and the complications of vaccine-induced type 1 diabetes alone outweighs the risk of HiB disease when not vaccinated. The vaccine is also associated with other adverse events such as asthma, allergies, epiglottitis, an increased incidence of HiB disease in the first week after vaccination, and more. The bottom line is the risk of death is higher with the vaccine than without.