nigīrṇaḥ - swallowed; api - although; asura-indreṇa - by the best of the demons, Vṛtrāsura; na - not; mamāra - died; udaram - the abdomen; gataḥ - reaching; mahā-puruṣa - by the armor of the Supreme Lord, Nārāyaṇa; sannaddhaḥ - being protected; yoga-māyā-balena - by the mystic power that Indra himself possessed; ca - also.

The protective armor of Nārāyaṇa, which Indra possessed, was identical with Nārāyaṇa Himself, the Supreme Personality of Godhead. Protected by that armor and by his own mystic power, King Indra, although swallowed by Vṛtrāsura, did not die within the demon’s belly.