Post-vaccination Geometric Mean Titers Research Articles

A lamb model for human respiratory syncytial virus infection.

Respiratory syncytial virus (RSV) is the most important cause of bronchiolitis and pneumonia in young children. The development of an animal model of RSV disease serves to better understanding the pathophysiology of airway disease from RSV infection in infants and children. Groups of six lambs were inoculated intratracheally (IT) or intranasally (IN) with a human strain of RSV (H-RSV). For controls 8 lambs received IT virus-free cell lysate. Tachypnea and fever were observed significantly more often following IT than following IN inoculation of H-RSV or IT placebo (for tachypnea: 20 of 69 days, 5 of 63 days, and 3 of 89 days, respectively, P < 0.001; for fever: 6 of 69 days, 0 of 63 days, and 1 of 89 days, respectively, P < 0.02). Nasal fluid production was significantly more frequent in both IT (14 of 69 days) and IN (15 of 63 days) groups than in the placebo group (2 of 87 days, P < 0.001). Postvaccination geometric mean titers (GMT, arithmetic transformation of log 2) of RSV-specific neutralizing antibody were significantly increased in the IT H-RSV group compared with postplacebo GMTs at 1 week (72 vs. 6.7, P < 0.03). By the second week postinoculation both H-RSV-infected groups had comparable levels of RSV-specific neutralizing antibody titers and had significantly greater GMTs for the second through to the fourth week than the placebo group (144, 128, and 4.8, respectively P < 0.0008). Bacterial isolates of the upper airway were comparable among the three groups. Histopathology at day 28 postinoculation was unremarkable for the three study groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunogenicity of Subcutaneous Versus Intramuscular Oka/Merck Varicella Vaccination in Healthy Children

To compare the immunogenicity and safety of varicella vaccine by either subcutaneous or intramuscular injection, 166 healthy children aged 12 months to 10 years old who had no prior history of varicella were enrolled from two pediatric practices and randomly assigned to receive 0.5 mL of a single lot of varicella vaccine. Sera from the day of and 6 weeks postvaccination were tested for varicella antibody by gpELISA. Parents recorded clinical events occurring in the 6 weeks following vaccination. In the 132 evaluable children, the mean prevaccination titer was 0.3 gpELISA units for both groups. Sixty-three (97%) of the 65 receiving varicella vaccine by the subcutaneous route seroconverted compared with 67 (100%) of 67 immunized intramuscularly. Postvaccination geometric mean titer in the subcutaneous group was 6.9 +/- 7.0 gpELISA units and did not differ significantly from the geometric mean titer of 10.5 +/- 4.4 in the intramuscular group. Varicella vaccine was generally well tolerated by either route; 21% of both groups complained of reactions at the injection site and 7% had a varicella-like rash. Although varicella vaccine is recommended to be given subcutaneously, the results of this study indicate that inadvertent intramuscular administration of varicella vaccine is not reason for revaccination.

Group C Neisseria meningitidis variant polysaccharide vaccines in children

The currently United States-licensed group C Neisseria meningitidis vaccine, composed of the O-acetyl-positive capsular polysaccharide, is poorly immunogenic and does not afford protection from disease to infants and young children. Group C N. meningitidis O-acetyl-negative polysaccharide vaccine induces higher titers in adults than does the O-acetyl-positive vaccine. We compared the immunogenicity of these vaccines in 2-year-old children. Reactions were minimal and did not differ between the two vaccines. The postvaccination geometric mean titer was twofold greater in the O-acetyl-negative group (1.58 versus 0.73 micrograms of antibody per ml). The rates of decline in titer were similar in both groups. Further study regarding immunogenicity of and the anamnestic response to the O-acetyl-negative vaccine is warranted in the age group (less than 18 months) at highest risk for invasive meningococcal disease.