In this section, we discuss specific agents that are currently affected by problems of supply.

Hepatitis A Vaccine

At present, there are two licensed hepatitis A vaccines in the U.S.: Vaqta® (Merck) and Havrix® (GlaxoSmithKline). Both of these products utilize an inactivated whole virus grown in human cell culture. Each of these brands has pediatric and adult dosage forms available. Although the dose is calculated differently between the two products, both are given as an initial injection with a follow-up injection in 6 to 12 months (Figure 1). Immunity is conferred to approximately 97% of patients receiving the first injection and 100% of patients receiving both injections (Table 1).
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Table 1 Updated Recommendations for Pneumococcal Conjugate Vaccine Use Among Healthy Children During Moderate and Severe Shortages — Advisory Committee on Immunization Practices, 2001

Age at First Vaccination

No Shortage*

Moderate Shortage

Severe Shortage

<6 months 2, 4, 6, and 12-15 months 2, 4, and 6 months (defer 4th dose) 2 doses at 2-monthinterval in 1st 6 months

of life (defer 3rd and 4th doses)

7-11 months 2 doses at 2-month interval; 12-15 month dose 2 doses at 2-month interval; 12-15 month dose 2 doses at 2-month interval (defer 3rd dose)
12-23 months 2 doses at 2-month interval 2 doses at 2-month interval 1 dose (defer 2nd dose)
>24 months 1 dose should be considered No vaccination No vaccination
Reduction in vaccine doses usedf 21% 46%

The hepatitis A vaccine now in short supply is Vaqta®. Specific lots of Vaqta® were recalled as a result of decreased anti-genicity of the product. Fortunately, GlaxoSmithKline has all Havrix® products available and is shipping them to customers and wholesalers without restriction.

The ACIP recommends that patients can receive either brand of product to complete their vaccination series. This type of substitution between brands is appropriate for other vaccines as well.

Hepatitis B Vaccine

Two brands of hepatitis B vaccine are currently available in the U.S.: Engerix-B® (GlaxoSmithKline) and Recombivax HB® (Merck). Both products are produced using recombinant technology and therefore contain no human blood products. The hepatitis B vaccine provides direct immunity against hepatitis B and indirectly against hepatitis D. Hepatitis B vaccines are administered as a three-injection series to confer immunity to recipients (Figure 1). Immunity is conferred to 70% to 80% following the second injection and to greater than 95% of recipients after all three injections (Table 2). An alternative two-injection schedule is available for adolescents 11 to 15 years of age, providing 99% seroprotection rates in this age group.
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Table 2 Seroconversion Rates Following Selected Doses of Multiple-Injection Vaccine Series

Vaccine

Seroconversion Rates Following Initial Dose Seroconversion Rate Following Dose 2 (If More Than Two-Dose Series) Seroconversion Rate upon Completion of Recommended Series
Hepatitis A

97%

N/A

100%

Hepatitis B

62%-65%

70%-80%

95%

Measles, mumps, and rubella

95%

N/A

99%

Prefilled syringes of Recombivax HB® is the hepatitis B vaccine that is currently in short supply. However, several other Recombivax HB products as well as Engerix-B are available and are being shipped to customers and wholesalers without restriction. The ACIP indicates that the two brands of hepatitis B vaccines are interchangeable. Therefore, physicians should not withhold vaccine when the brand of product available differs from that of the product used to initiate the series.

Haemophilus influenzae Type b Conjugate Vaccine

The Haemophilus b conjugate vaccine is indicated for prevention of infection from Haemophilus influenza type b (Hib). Several brands of Haemophilus b conjugate vaccine are commercially available. Each formulation utilizes purified capsular polysaccharide of Hib conjugated via covalent bonding to another antigen to increase immunogenicity. Another product contains a combination of Hib vaccine and hepatitis B vaccine. Adults and children 15 months of age or older need only one injection of Hib vaccine, whereas children under 15 months of age receive two doses (see Figure 1).

Figure 1. Recommended childhood

Figure 1. Recommended childhood immunization schedule*—United States, 2002. (From CDC. MMWR, January 18, 2002.)

Currently, the products in short supply are PedVaxHIB® (Merck) and the combination product COMVAX®. Aventis Pasteur is currently shipping its product, Act-HIB®, without restrictions, and therefore no patients should be affected by these supply problems.

Measles, Mumps, and Rubella Virus Vaccine Live

The measles, mumps, and rubella virus vaccine (MMR) is a combined live virus vaccine. The product is given as a two-dose series for children or adults, although the administration schedule differs between these two groups. The only manufacturer of MMR in the United States is Merck, thus rendering the shortage of this product a significant problem. The current shortage is due to unspecified manufacturing problems. As of March 2002, more than one million doses of MMR were on back order for both the public and private sectors. Merck’s individual measles and rubella vaccines are also in short supply. This shortage was projected to be resolved by late summer 2002.

During this shortage:

•  infants should get their first dose of vaccine on schedule.

•  the second dose of vaccine can be delayed until the shortage is resolved.

Nearly 95% of those receiving a single dose of MMR vacccine develop protective antibody within 2 weeks of the dose. The additional injections recommended by the ACIP are designed to provide the remaining 5% of people an additional chance to se-roconvert. Thus, delaying the initiation of a vaccine series may expose a subject to greater risk of disease than not completing a vaccination series. In the event that the shortage persists, patients may be at an increased risk of contracting one of these diseases as population immunity wanes. Serologies performed during a measles outbreaks have shown that those who have not completed their vaccine series are at an increased risk of contracting the disease. This suggests that herd immunity alone does not exclude the possibility of an outbreak. Therefore, it is imperative that delayed vaccinations be tracked in such a way as to ensure vaccination upon resolution of the shortage.

Category: Diseases / Tags: Principles, Vaccine Shortages

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