A study has been released by U.S scientists working for the Centers of Disease Control, Atlanta, that suggest immunity from chickenpox conferred by Varicella vaccine may wane over the years, and even result in a more severe form of the disease. The study findings encourage a booster dose of the vaccine.
In the surveillance data, children vaccinated five or more years earlier were 2.6 times more likely to have a moderate-to-severe breakthrough case of chickenpox than those who had been vaccinated more recently.
Lead researcher Sandra S. Chaves and team have reported that the breakthrough varicella rate eight years after vaccination, was 12 times higher than in the first year after vaccination, even accounting for changes in exposure.
Findings were published in the New England Journal.
Says Chavez who came about the findings after following a sentinel population of 350, 000 subjects for 10 years after the implementation of universal varicella vaccination in 2005, " Waning of immunity is of particular public health interest because it may result in increased susceptibility later in life, when the risk of severe complications may be greater than that in childhood."
Dr. Jane Seward, one of the authors of the study and an official at CDC, Atlanta, said that researchers decided to embark on the study after noticing outbreaks were happening despite vaccination programs.
Seward said the chickenpox vaccine provides 85 per cent protection, but of the remaining 15 per cent, most will get mild cases of chicken pox -- with a small number getting more severe illness.
It has been demonstrated that immunity from varicella vaccination wanes among health care workers in terms of measurable antibodies, but this is the first study to demonstrate that vaccination-induced immunity breaks down over time in children.