[2][3] In countries that include it as a routine vaccine, rates of severe Hib infections have decreased more than 90%.

[4] It is recommended by both the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC).

[2] An initial Hib vaccine consisting of plain (unconjugated) type b polysaccharide, was introduced in the United States in 1985.

The vaccine has also been shown to be immunogenic in patients at high risk of invasive disease.

[12] Similar reductions in Hib disease occurred after introduction of the vaccine in Western Europe[13] and developing countries.

[15] Clinical trials and ongoing surveillance have shown the Hib vaccine to be safe.

The most common reactions are mild fever, loss of appetite, transient redness, swelling, or pain at the site of injection, occurring in 5–30% of vaccine recipients.

However, the antibody response to PRP was quite variable in young children and diminished rapidly after administration.

[16][17] PRP covalently linked to a protein carrier was found to elicit a greater immune response than the polysaccharide form of the vaccine.

As a result, the age group with the highest incidence of Hib disease was unprotected, limiting the usefulness of the vaccine.

Also, post-licensure studies by Michael Osterholm[22] and his colleagues,  and Dan M. Granoff et al.[23] suggested that the PRP vaccine was largely ineffective in preventing invasive Hib disease in children 18 to 59 months, the age group recommended for vaccination .

[25] This vaccine was based on work done by Lasker Award-winning American scientists John Robbins and Rachel Schneerson[26] at the U.S. National Institutes of Health, and Porter Anderson and David Smith then at Boston Children's Hospital.

[16] The Hib vaccine using a meningococcal outer membrane carrier protein has unique immunostimulatory properties, eliciting an anticapsular response to a single injection given to infants as young as 2 months of age.

[30] In contrast, Hib conjugate vaccines using other protein carriers require two or three injections to reliably elicit anticapsular antibody responses in infants less than six months of age.

The World Health Organization (WHO) has certified several Hib vaccine combinations, including a pentavalent diphtheria-pertussis-tetanus-hepatitis B-Hib, for use in developing countries.