Rationale: Currently implemented measures to contain the avian flu use the knowledge of comparable epidemics as the global outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003. In order to control the avian plague not only epidemiological aspects should be considered. Important will be the fact that preventive measures can be interpreted as public goods. Hence, provision policies are influenced by public good's characteristics as non-rivalry, non-excludability and the technology on public supply aggregation. Particularly, the aggregation technology has an important influence on policy recommendations. Yet, its impact is often neglected. Objectives: By using the concept of aggregation technology, this paper aims at investigating whether or not countries' national efforts against the avian influenza are adequate from an international point of view. Or, should international organizations like the World Health Organization intervene, because H5N1 has been spread beyond national borders? Methodology: This paper applies a game theoretic analysis of inter-country relationships. In standard analyses which have neglected the variety of aggregation technologies and, hence, assume a summation technology, countries' behaviour results in a Prisoner's Dilemma. In contrast, our model focuses on the weakest-link public good prophylactic measures against H5N1. Thus, an assurance game underlies where each country matches the others effort to contain the avian flu's spread. Hence, countries have no incentive to free ride, because smaller efforts than the efforts of the weakest-link country affect all. Results: International support by an international organization is not a needed. Preventive measures provided at the national level yields to an efficient international provision level. Such a solution is, however, only recommendable, if countries possess the same income and endowment. If, however, poorer countries do not have resources to achieve an adequate response to H5N1, far-reaching countries are put at risk due to migratory birds. In such a case, national efforts results in a suboptimal provision at the national level as well as beyond national borders. This is caused by the underlying weakest-link technology. Thus, industrialized countries should support poorer countries. Conclusions: These results make clear that an intervention of international organizations is not necessary a desirable recommendation, even if the avian influenza's spread has reached an international range. National efforts can give an adequate response to a global problem. Moreover, additional long-term interventions such as structural changes in the poultry sector are necessary to prevent further outbreaks