Primary vs Secondary Coverage
Primary coverage pays your claim first, regardless of other insurance you hold. Secondary coverage pays only what remains after your health insurance or credit-card cover has responded — slower, with more paperwork.
With secondary medical coverage, a claim from a Tanzanian clinic first goes to your domestic health insurer — which may cover nothing abroad — and only then to your travel insurer, with documentation of the denial. Primary coverage skips that round trip entirely.
For safari travel the practical difference is speed and guarantees: remote-area providers and evacuation services want payment guarantees now, and a primary insurer with 24/7 assistance can issue them directly. If your policy is secondary, at minimum know your health plan's overseas rules before departure.