Indian drugmaker Zydus Cadila said on Thursday it has applied for emergency use approval of its three-dose Covid-19 vaccine that showed efficacy of 66.6% in an interim study and could become the second home-grown shot if regulators consent.

Although coronavirus infections have dropped from a devastating peak in April and May that strained healthcare facilities, experts have warned of a third wave, saying widespread vaccination is one of the best pandemic defences.

Zydus' vaccine ‘will certainly help in ramping up India's overall vaccination drive as it would be the fifth approved,’ Prashant Khadayate, a pharmaceutical industry analyst at GlobalData said.

Zydus said the efficacy result is based on an interim analysis of a late-stage trial of more than 28,000 volunteers nationwide, including nearly 1,000 subjects in the age group of 12 to 18.

The drugmaker said it was evaluating a two-dose regimen for the shot.

If approved, ZyCoV-D will be the world's first DNA vaccine, Zydus said, as it makes use of a portion of the genetic code - DNA or RNA - in the SARS-CoV-2 virus to stimulate an immune response against its spike protein.

DNA vaccines differ from other approved Covid-19 shots, which are based on new mRNA technology such as in those from Pfizer and Moderna, and established technology like viral vectors, as with AstraZeneca.

Zydus, which aims to produce up to 120 million doses annually, said its study coincided with the peak of India's second wave of infections and affirmed its efficacy against new mutants, especially the Delta variant.

It did not, however, disclose its efficacy against those variants.