Two new studies emphasize the importance of delivering measles and influenza vaccines to HIV-infected individuals. Both studies are published in the August 1 issue of The Journal of Infectious Diseases.
William J. Moss, MD, and colleagues at the Johns Hopkins University and elsewhere studied immune responses to measles vaccine in HIV-infected and uninfected children in Zambia from 2000 to 2004, when measles endemic in a country that still has one of the highest HIV prevalence rates in the world. Measles poses a greater fatality risk in HIV-infected children than in uninfected children.
Measles vaccine was administered in both groups at age 9 months. This is the age recommended for infants who are not HIV-infected, but it is commonly also the age when HIV-infected infants are vaccinated against measles. Children were followed for up to 27 months thereafter. Some received repeat vaccination. Measles-specific antibodies in the blood were then measured on subsequent visits.
Dr. Moss and colleagues found that although 88 percent (44 of 50) of HIV-infected children developed protective antibody levels within 6 months of vaccination, during 27 months of follow-up "only half of the  HIV-infected children who survived maintained protective antibody levels, compared with almost 90 percent [63 of 71] of the HIV-uninfected children." In contrast, 92 percent (11 of 12) of HIV-infected children who were vaccinated a second time during follow-up had protective antibody levels.
Thus, measles antibody levels in HIV-infected children rapidly diminish following vaccination, emphasizing the importance of supplementary vaccinations to maintain immunity. According to Moss, "Because measles virus needs only a small proportion of susceptible children to sustain transmission and cause outbreaks, these vaccinated but susceptible HIV-infected children could impede measles elimination efforts in regions of high HIV prevalence."
A second study examined influenza vaccination among HIV-positive individuals in the United States. Although federal guidelines have recommended yearly influenza vaccination for HIV-infected individuals since the early 1990s, a survey by the U.S. Centers for Disease Control and Prevention (CDC) shows actual influenza vaccination coverage of high-risk individuals, including HIV-infected persons, to be only 24 percent in adults age 18 to 49 and 46 percent in ages 50 to 64.
These rates are notably lower than the federal target of 60 percent coverage for all at-risk groups and contrast with rates as high as 92 per cent for HIV-infected persons in countries with near-universal health care. "This low vaccination coverage leaves a lot of HIV-infected persons at risk for acquiring seasonal influenza," said Kathleen M. Gallagher, DSc, MPH, lead author of the current study.
Dr. Gallagher and a team of researchers from the CDC and elsewhere analyzed data from medical records of 51,021 HIV-infected patients from 10 U.S. cities between 1990 and 2002. Results from the study showed that rates of influenza vaccination increased from 28.5 percent in 1990 to 41.6 percent in 2002, with the upward trend associated with the advent of improved HIV therapy beginning in the mid-1990s. Those receiving antiretroviral drugs were more likely to be immunized for influenza, whereas those with higher viral loads and lower CD4 cell counts were less likely to receive the vaccine.
The authors concluded that while vaccination rates have improved in recent years, "substantial gains must occur in order to ensure protection against seasonal influenza" and to meet the 60 percent federal target.
In an accompanying editorial of the two studies, Rita F. Helfand, MD and colleagues at the CDC noted: "The strategy for achieving rapid reduction in measles mortality has four components: 1) improving routine immunization coverage to greater than 90 percent in every district, 2) providing a second opportunity for measles immunization, 3) implementing effective measles surveillance, and 4) improving case management (e.g., with vitamin A and antibiotics)." These methods would serve not only to protect individuals at high risk for acquiring these diseases, but to protect the population from infection as well. Helfand points out that "in addition to the challenges of protecting HIV-infected children, [Moss's] study also reminds us that HIV may only be one of the challenges to achieving high population immunity."
1) During three years of follow-up following measles vaccination among children in Zambia, only half of the HIV-infected children who survived maintained protective antibody levels against measles, compared with almost 90 percent of the HIV-uninfected children.
2) Rates of influenza vaccination among HIV-infected adults in the United States increased from 28.5 percent in 1990 to 41.6 percent in 2002, but remained well below the federal goal of 60 percent.
3) Countries with more universal access to health care have reported influenza vaccine coverage rates as high as 92 percent among their HIV-infected population.
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