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Delayed BCG Vaccine May Improve Immune Response Against TB

Posted Oct 14 2009 10:02pm
From Reuters Health Information
By C. Vidya Shankar

NEW YORK (Reuters Health) Sep 04 - BCG vaccine administered at 10 weeks of age produces a better immune response against Mycobacterium tuberculosis than when given at birth, according to the results of a small study from South Africa, published in the September issue of Vaccine.

The protective effect of BCG against tuberculosis varies depending on such issues as the vaccine strain, the route of administration, dose and host immune response, Dr. Willem Hanekom and colleagues explain. As the cell-mediated immune response is "immature" at birth, delaying the vaccine could enhance the immune response, they propose.

To test their hypothesis, Dr. Hanekom, from the University of Capetown, and his team conducted a randomized trial in which 25 neonates received BCG vaccine by intradermal injection at birth, whereas 21 received it at ten weeks of age. Infants in both groups were born healthy at term to HIV-negative mothers, and had no contact with tuberculosis.

The immune response to BCG was assessed 10 weeks and 1 year after vaccination by assay of the cytokines interferon gamma, tumor necrosis factor-alpha, and Interleukin-2, all produced by T helper 1 CD4 T cells.

Cytokine production by BCG-specific CD4 T cells were significantly greater among the delayed vaccine group both at 10 weeks and 1 year after vaccination, they observed. The response was most significant one year after vaccination, they note.

"Delayed vaccination resulted in an enhanced memory CD4 T cell response at 1 year of age," Dr. Hanekom observed. This results in improved long-term immunity, "particularly of the kind regarded as important for protection against TB," he explained.

The researcher noted that delayed BCG vaccine resulted in an increased production of "polyfunctional" BCG-specific CD4 T cells. "Polyfunctional cells make multiple cytokines together -- we think these cells are important for protection against TB," he said.

If these findings are confirmed by larger studies, they "could have wide-ranging implications for BCG vaccination practices, world-wide," Dr. Hanekom concluded.

Vaccine 2009;27:5488-5495.
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