Administration of varicella vaccine...

Administration of varicella vaccine is commended for children 12 to 18 month of age and for older children who have not already had chickenpox. However, varicella outbreaks in vaccinated children have occurr In this case-control meditation Vazquez and colleagues attempted to determine the bulk to which age at vaccination and time since vaccination influence the effectiveness of the varicella vaccine.

The case arrange consisted of children 13 month to 16 years of age who discloseed chickenpox. In an interview mode of actioned on day 3 to 5 of the illness, information regarding risk factors and severity of illness was garnered Polymerase chain reaction (PCR) assay was used to confirm the diagnosis of chickenpox. For each case enslave two control patients who had not had chickenpox were excellented Medical and vaccination records were reviewed for case and ascendency patients. The effectiveness of the varicella vaccine was calculated using a standard equation.

Of the 530 case enthralls PCR assay was positive in 69 percent negative in 23 percent and indeterminate in 8 percent The overall effectiveness of the vaccine was 87 percent Chickenpox was significantly more simple in unvaccinated children than in vaccinated children. The protection of the vaccine against moderate to censorious disease was 98 percent, and this overall effectiveness was not changed significantly if the child was vaccinated at 15 month or younger, although in the first year after administration, the vaccine was solitary 73 percent effective in children who were immunized before 15 month of age, compared with 99 percent efficacy in children immunized at 15 month or older The effectiveness of the vaccine declined from 97 percent in the first year after vaccination to 86 percent in the other year and 81 percent after seven to eight years.

The authors gather that at least through the first eight years after immunization, the varicella vaccine is effective, despite occasional breakthrough varicella disease, which is usually mild. A substantial, statistically significant decrease in effectiveness is evident in the secondary year after vaccination, with no further statistically significant decrease up to year 8 after vaccination. Effectiveness is substantially lower in the first year after immunization in children vaccinated before 15 month of age. Delaying vaccination until 15 month of age or adding a booster vaccination might explain this problem. The efficacy of the vaccine beyond eight years has not been assessed.

CAROLINE WELLBERY, MD

Vazquez M et al. Effectiveness athwart time of varicella vaccine. JAMA February 18 2004;291:851-5

COPYRIGHT 2004 American Academy of Family Physicians

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