I imagine that if you want to administer vitamin A to children periodically, this follows studies which have shown the necessity in other words the deficiency within this target and this despite the fact that they are already receiving micronutrients containing of vitamin A. If this is the case I think that there is less risk of overdose especially if the administration respects the minimum interval of 6 months and that the doses of vitamin A are adapted to the age of the children (100,000 IU for children aged 6-12 months and 200,000 IU for children aged 12-59 months).

The effectiveness of vitamin A supplementation, even in populations with diverse diets and access to multivitamins, can vary based on several factors:

Prevalence of Vitamin A Deficiency: If the population has a high prevalence of vitamin A deficiency, supplementation can be beneficial in reducing the risk of deficiency-related health issues, such as impaired immune function and vision problems.

Coverage and Compliance: The effectiveness of supplementation programs depends on the coverage and compliance rates within the population. If a significant portion of the target population receives and adheres to the supplementation regimen, the program is more likely to have a positive impact on vitamin A status.

Dietary Diversity: While a diverse diet can provide various nutrients, including vitamin A, the bioavailability of vitamin A from plant-based sources (provitamin A carotenoids) may be lower compared to animal-based sources (preformed vitamin A). Therefore, supplementation can still be beneficial, especially for individuals with limited access to animal-derived foods.

Nutritional Status: The nutritional status of individuals within the population, including factors such as malnutrition, gastrointestinal disorders, and chronic illnesses, can influence the effectiveness of vitamin A supplementation. Individuals with underlying health issues may have higher requirements for certain nutrients, including vitamin A.

Age and Vulnerability: Children under 5 years old are particularly vulnerable to vitamin A deficiency due to rapid growth and development. Supplementing this age group with high-dose vitamin A can help prevent deficiency-related complications, such as night blindness and increased susceptibility to infections.

Supplementation Strategy: The timing, dosage, and frequency of vitamin A supplementation can impact its effectiveness. Programs that provide high-dose supplements at appropriate intervals, such as every 6 months as recommended by the World Health Organization, are more likely to achieve desired outcomes.

In summary, while diverse diets and access to multivitamins can contribute to overall nutrient intake, vitamin A supplementation remains an important intervention in populations at risk of deficiency, particularly young children. However, the effectiveness of supplementation programs depends on various factors, including coverage, compliance, dietary patterns, and individual health status. It's essential to tailor supplementation strategies to the specific needs and characteristics of the target population to maximize impact.

There should be no concern with the children taking the daily supplements in addition to twice-yearly VAS, especially in a refugee situation where micronutrient deficiency is likely high among young children. The %RDA in the vitamin is very low. In fact, its probably best to have both interventions simultaneously - the vitamins will contribute to slowly improving vitamin A status, while the VAS helps reduce morbidity and mortality associated with vitamin A deficiency.

Do the refugees have access to the country's current VAS program? You may want to check to see if there is some access, as you don't want to risk double-dosing children with high-dose VAS. There may also be supply of vitamin A capsules available within the country, rather than having to seek an additional supply for the refugee population.

High-dose vitamin A supplements and multivitamins in children in the micronutrient area:

High-dose vitamin A supplements and multivitamins have been demonstrated to be beneficial in lowering morbidity and mortality rates in children under five years of age. A review of studies conducted in low- and middle-income countries found that vitamin A supplementation was linked to a nearly 24% reduction in the overall risk of death among children afflicted with vitamin A deficiency.

Vitamin A supplements and multivitamin interventions are crucial in addressing the consequences of vitamin A deficiency, including increased morbidity and mortality due to weakened immune systems, slowed growth and development, and visual system disorders such as xerophthalmia and irreversible blindness. The supplementation of vitamin A has been recognized as a safe, cost-effective, and efficient means for eliminating its deficiency and improving child survival through vitamin A supplementation; this is an essential public health intervention, particularly in disaster-affected areas.

Anonymous 45847 is correct. There is a myth that biannual high dose vitamin A supplementation is indicated for dealing with vitamin A deficiency at community level. It's purpose is not that. It is to reduce mortality. This myth is furthered by the fact that mortality is too difficult to use in evaluating the impact of a program, so sometimes levels of vitamin A deficiency in the community are recommended. However, barring any other intervention related to improving diets, who effective the distribution was will be completely determined by coverage levels and how long after the high dose was given that the blood samples are taken. 

Each high dose of vitamin A has only a temporary impact on serum retinol, at first making it go far too high, but this does not last; depending how low the baseline retinol levels were and the diet/continued vitamin A intake, one to four months after receiving the dose, the child is back to something close to the retinol level he or she had before receiving the high dose. 

Many thanks everyone, this has answered my question. To answer some of the points raised here, the refugee population we are serving are from areas with endemic vitamin A deficiency, the diet is very poor due to poor quality food served in the camps, and there is no other government program (or otherwise) to provide supplementation. Really helpful input from all, again, many thanks.