Latest research shows the chickenpox vaccine loses some of its effectiveness in the first year after vaccination. Parents are encouraged to vaccinate their children against chickenpox between 12 months and 18 months. Consequently, researchers were prompted to further investigate the vaccine after chickenpox outbreaks were reported among vaccinated individuals.
Researchers studied nearly 350 children ages 13 months or older who had been afflicted with the chickenpox virus.The research shows the effectiveness of the vaccine in its first year to be 97 percent. It then drops to 84 percent after two to eight years.
However, the overall effectiveness of the vaccine was 87 percent.Research points to age as a potential factor in the difference. The effectiveness of the vaccine was lower in children 15 months old or younger (73 percent) than in children who were 15 months or older (99 percent) when they were given the vaccine.
Researchers conclude, "...in the United States, deaths from varicella and other complications in immunocompetent persons still occur and will continue to occur until the infection in eliminated. It is important to monitor closely the incidence of varicella an the effectiveness of the vaccine over time to determine if a booster dose is needed to improve its effectiveness."