The CDC’s Pink Book chapter on Hib

The interspecies competition library

Sisyphus, part two

Protective effect of breastfeeding against invasive h influenzae disease.

More on Hib

Manufacturer’s Inserts and efficacy statements:

Pedvax HIB- Efficacy of Hib ranged from 59-98%

However, those studies are showing the rate of effectiveness against vaccine serotype only.

In this study over a six year period (2000-2006) researchers came to the conclusion that:

In addition to the proportional increase in cases of nontype b Haemophilus influenzae disease in the post H. influenzae type b vaccine era, the incidence of invasive H. influenzae disease was found to be approaching the rates of H. influenzae type b disease that were documented in the prevaccine period. Fifty-six percent of invasive disease now occurs in individuals aged >10 years.

The same finding was reported in the US reported figures as well (page 5 begins Haemophilus information).

A study on Invasive Haemophilus influenza in adults turned up an interesting tidbit:

Though numbers of Hib infections in adults fell after the introduction of Hib vaccines for children (P = 0.035), and there was no increase in infections caused by other capsulated Hi serotypes, total numbers of invasive Hi infections increased due to a large rise in infections caused by non-capsulated Hi (ncHi) strains.

A study focusing on the characteristics of invasive Hib in adults noted:

RESULTS: During January 1996-December 2004, 770 cases of invasive H. influenzae disease were reported to the Illinois Department of Public Health (Springfield). The incidence of disease increased from 0.4 to 1.0 cases per 100,000 persons, including an increase of incidence in adults aged > or = 65 years from 1.1 to 3.9 cases per 100,000 persons. Nontypeable H. influenzae disease accounted for the greatest proportion of cases (35.8%-61.5%) in all but 1 age group. The number of cases of invasive nontypeable H. influenzae disease increased by 657%, from a low of 7 cases in 1996 to a high of 53 cases in 2004; as a proportion of annual cases, nontypeable H. influenzae disease increased from 17.5% in 1996 to 70.7% in 2004. Overall, the case-fatality rate was 12.7%, with the highest rate observed in persons aged > or = 65 years (20.6%). The case-fatality rate was similar for the hospital discharge database and for Indiana, Maryland, Oregon, and Wisconsin (range, 12.9%-18.2%).

Incidence of Haemophilus influenzae type b meningitis during 18 years of vaccine use: observational study using routine hospital data suggests in their comments how to better determine actual effectiveness. (Currently methods such as ELISA are used to determine clinical efficacy as stated in package inserts, by using a biochemical technique to determine the presence of antibodies.)

Epidemiological data are probably more relevant than antibody measurements, which are not always correctly interpreted. The surrogate antipolysaccharide antibody concentrations of 0.15 μg/ml for short term and of 1.0 μg/ml for long term likely protection (determined by our group)5—still taken by many as surrogate markers for clinical effectiveness—applied to Hib polysaccharide; for conjugate vaccines, we simply do not know what the “protective” antibody concentrations are. Instead, what we can quantify is a vaccine’s clinical effectiveness.

Estimating Haemophilus influenzae type b vaccine effectiveness in England and Wales by use of the screening method is one study discussing the possibility of having to add additional shots (as boosters) due to a resurgence in Hib.

Initially, the rate of invasive Hib disease decreased dramatically but has been increasing since 1999. To determine possible reasons for this increase, the effectiveness of Hib conjugate vaccine was estimated by use of the screening method.

Vaccine effectiveness was estimated to be 56.7% (95% confidence interval, 42.5-67.4). Effectiveness was lower in children vaccinated during infancy, compared with those who were vaccinated during the catch-up campaign (P=.0033), declined with time since vaccination (P=.0008), and was lower in children born during 2000-2002, compared with other children scheduled for infant vaccination (P=.0041). Use of a catch-up vaccination program enhanced the control of Hib infection in England and Wales. Since 1999, however, low effectiveness in infants, declining effectiveness with age, and the use of lower-efficacy vaccines have contributed to increased rates of Hib infection.

Hib also has flagging effectiveness against pneumonia, as is demonstrated in this Brazilian study published in the International Journal of Epidemiology. Similar results have been seen in Chilean and Gambian studies.

By using conditional logistic regression the vaccine effectiveness was estimated as 31.0%.

In a large-scale field trial conducted in the Gambia, the Hib vaccine efficacy on pneumonia was found to be 21% using the same radiological end-point as the present study.

In Chilean children, a reduction of 22% of radiologically confirmed pneumonia was detected in a retrospective investigation of discharge diagnoses by chart review.

The Journal of Infectious Diseases published Prevention of Haemophilus influenzae type b (Hib) meningitis and emergence of serotype replacement with type a strains after introduction of Hib immunization in Brazil in January 2003 which had findings of:

The incidence of Hib meningitis decreased 69% during the 1-year period after initiation of Hib immunization (from 2.62 to 0.81 cases/100,000 person-years; P<.001). In contrast, the incidence for H. influenzae type a meningitis increased 8-fold.

Therefore, Hib immunization contributed to an increased risk for H. influenzae type a meningitis through selection of circulating H. influenzae type a clones.

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