We anticipate that results from this proposed effort will provide the evidence required for global policy changes towards single-dose vaccination programs, if non-inferiority of one-dose is demonstrated, and lead to a better understanding of antibody levels required for protection. If one-dose protection is observed in these first four years, follow-up might need to be extended by at least six years to assess durability of the response to vaccination. If one dose of either vaccine is found to be inferior to two doses, our study will also provide estimates of the impact of single dose vaccination versus none, so that policy makers in regions where widespread vaccination programs have yet to be implemented can consider the decrement in efficacy of one versus two dose vaccination in light of the estimated public health impact of a single-dose program. Finally, the proposed work holds the potential to transform current approaches to vaccine development, as it could provide the first example of a single dose (prime only) subunit vaccine that induces durable and protective (sterilizing) immunity.