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[LUSAKA] Children infected with HIV may require repeated measles vaccination to gain adequate protection, according to new research.

The study in Zambia — published in the Journal of Infectious Diseases next week (1 August) — found that compared with healthy children, HIV-infected children were less able to maintain protective levels of antibodies against measles after an initial vaccination.

The results suggest that a second vaccination is important in regions of high HIV prevalence to protect HIV-infected children, maintain 'herd' or group immunity and to bolster measles elimination efforts.

Measles, caused by a virus of the Paramyxovirinae family, remains an important cause of child mortality in sub-Saharan Africa, says William Moss, lead author of the study and an associate professor at the US-based Bloomberg School of Public Health at the Johns Hopkins University.

According to the researchers, the measles virus only needs a small number of susceptible children to cause outbreaks, so it is important that as many children as possible have immunity to the virus.

The researchers studied the immune response to the measles vaccine in 696 healthy and HIV-infected children, aged 2-8 months.

Within six months of measles vaccination at nine months of age, 88 per cent of HIV-infected children developed protective antibody levels, as did 94 per cent of children who did not have HIV.

But after a further 27 months, only half of the surviving HIV-infected children maintained antibody levels high enough to protect against measles, versus almost 90 per cent of healthy children.

The results of the study show that sufficient resources must be invested in maintaining high levels of population immunity against measles in regions of high HIV prevalence, says Moss.

The World Health Organization already recommends vaccinating children for measles a second time, either through repeated immunisation campaigns or a routine second dose delivered through the primary healthcare system.

But despite recent progress in measles control, obstacles to eliminating the disease exist, including insufficient resources and lack of political will.

"The study is important because it shows the impact HIV has on the nation and sends a message to the government to double its effort on measles vaccination," Chansa Nkonga Mwangilwa, from Zambia's University Teaching Hospital and co-author of the study told SciDev.Net.

The authors recommend that additional research be conducted to determine the duration of measles immunity in HIV-infected children who are receiving antiretroviral therapy, and their response to revaccination against measles.

Link to full paper in the Journal of Infectious Diseases 

Reference: Journal of Infectious Diseases 196, 347 (2007)