Haemophilus influenzae type b conjugate vaccines - Its use and drawbacks

Normally in an immunization schedule we have till date seen 6 important vaccines consisting of BCG for tuberculosis, OPV for polio and DPT for diphtheria, tetanus and pertusis (whooping cough). In last few years hepatitis B vaccine has also been widely recommended.

Now when a parent visits a pediatrician for vaccination, they get a long list of vaccines to be given and this confuses the parents to a great extent in deciding whether to follow the doctors list or not. Among the vaccines prescribed other than those scheduled in EPI Hib or human influenza b vaccine is one of the most common vaccine.

When HiB vaccine should be started and it protects from which disease?

HiB vaccine protects against infection with N. infuezae bacterial infection which causes many diseases like otitis media, encephalitis and leaves permanent sequelae in the form of deafness or mental retardation in children.

A new born is protected from HiB by transplacental maternal antibody till 6-8 weeks. Acquired immunity develops in a baby only at 18 -24 months of age following subclinical infections. Hence the baby is susceptible from 6 weeks to 18 months and the HiB disease peaks during this period.

Which type of vaccine is HiB vaccine?

Hemophilus influenzae B is a capsular polysaccharide vaccine, so it is not a T cell dependent vaccine and there is no memory cell production. Hence there is no booster effect of this vccine when given for the second time. It is a B cell dependent vaccine, so only IgM is produced without IgG. So this is effective only in children above two years of age. On the contrary the disease prevalence of invasivw HiB disease is mostly below 18 months of age, with peak incidence around 6-9 months.

When a polysaccharide vaccine is conjugated with carrier protien, the conjugate vaccine will be effective from an earlier age even from 6 weeks of age, thus production against this disease is achieved from earlier age which is wanted. Now a days various conjugate vaccine HiB vaccines which are available, have made it possible to use HiB vaccine safely and effectively in the age when it is needed.

How long HiB vaccine is required to protect a child

The prevalence of Human influenza B disease is restricted to less than 5 years old children, hence two normal dose with a booster is sufficient to protect the child upto 5 years of age. Being a vaccine intended for boosting the immunity even the dosage are age related, for example 3 doses below 6 months, 2 doses between 7 to 11 months and a single dose after 1 year of age. All three schedules are followed by a booster dose AT 18 months of age. If HiB vaccine is administered for the first time beyond 15 months of age, a single dose is sufficient to evoke the required antibody response.

Can we postpone HiB vaccine to later age to reduce number of dosage

This is not advisable at all. The most vulnerable age of HiB infection is 6 weeks to 1 year. If the children are unprotected at this age then the whole purpose of HiB vaccination is not served. Mortality and morbidity are very hig if the child suffers from invasive HiB infection at a young and tender age.

What is the effect of HiB vaccination in India

In India the Indian acedemy of pediatrician has included HiB in the immuization schedule. It is given by a small percentage of pediatricians only in cities which covers only a small population. As HiB immunization is not in the Universal immunization program, nor it is given in any states or by any voluntary organization, so overall HiB coverage is meager in India.

Should HiB vaccination be considered in Expanded Program of Immunization (EPI) schedule in India

Though logistic is not supportive but if some voluntary organization come up with their support in any State then HiB vaccination should definitely be incorporated. In long run, considering the burden of disease, HiB should be included in National immunization program.

What are the formulation and combination of vaccines and is there any adverse effect

At present there are four formulations namely PRP-D, HbOC, PRP-OP and PRP-T. Three combiations are available in India namely DTwP/HiB, DTwP/Hepatitis B/HiB and DTap/HiB.

More details about HiB vaccine formulations, dosing, adverse effect etc can be seen at Types of HiB vaccine, its dosing and side effects.