Vitamin A plays a critical role in proper immune function, it has been used successfully to prevent and treat measles and to treat chicken pox.
Preliminary research shows that supplemental vitamin A improves the likelihood that the measles vaccine will provide protection. Vitamin A has, since the 1920s, been the subject of much research into the prevention and treatment of childhood exanthems, particularly measles. This nutrient has a critical role in proper immune function, and there is evidence that supplementation with vitamin A reduces the incidence and severity of, and deaths from, childhood measles. The World Health Organization (WHO) has therefore recommended that children with signs of deficiency receive supplementation with vitamin A. The recommended amounts are 100,000 IU for children younger than one year and 200,000 IU for children older than one year, immediately upon diagnosis, and repeated once the next day and once in one to four weeks. A controlled trial of African children given vitamin A supplementation according to the WHO's recommendations found that severity of measles and its long-term consequences were reduced by 82% on day eight, 61% in week six, and 85% six months after the onset.
Another controlled trial found that giving approximately 200,000 IU of vitamin A once during measles illness was not adequate to provide any benefit in African children whose vitamin A status was unknown. In a controlled prevention study, Indian children treated with 2,500 mcg (8,333 IU) of vitamin A weekly had fewer measles complications and less than half of the rate of death as compared with children receiving placebo; but in another study, Indian children receiving 200,000 IU of vitamin A every six months did not have a different rate of total infectious illness nor rate of death as compared with children receiving placebo.
An analysis of 20 controlled trials concluded that vitamin A supplementation reduced deaths from measles respiratory infection by 70%. While vitamin A deficiency is widespread in developing countries, it has also been reported in the United States and has been linked with more severe cases of measles. The American Academy of Pediatrics has recommended supplementation with vitamin A for children between the ages of six months and two years who are hospitalized with measles and its complications. The recommended amount is a single administration of 100,000 IU for children aged 6 to 12 months and 200,000 IU for children older than 1 year, followed by a second administration 24 hours later and a third after four weeks in children who are likely to have vitamin A deficiency.
One trial showed that low levels of vitamin A are more prevalent in children with measles than in similar children without measles, with levels rising back to normal several days after the onset of the infection. This observation led the authors of the study to conclude that vitamin A deficiency is a consequence of infection with the measles virus and to recommend supplementation with vitamin A during measles infection even when prior deficiency is not suspected. Vitamin A stores have also been shown to be depleted during chicken pox infection, and some preliminary data supports its use in treatment of chicken pox. In a controlled trial, in which children without vitamin A deficiency were given either 200,000 IU of vitamin A or placebo one time during chicken pox, the children given vitamin A had shorter duration of illness and fewer severe complications. The researchers then treated the patients' siblings with vitamin A before chicken pox became evident, and they had an even shorter length of illness.