The short answer: It's just one of many Newcastle disease vaccines but it's a godsend for village chickens. Commercial ND vaccines work fine when chickens are under good control and are housed full-time but conditions in the village are different. This is where the I-2 vaccine excels.
The medium answer: There are lots of ND vaccines but this one is special. Here's a brief how and why.
The long answer: Well, we'll spare you that but there is a well written article with more background here. But I still reckon the full story is fascinating - it could fill a book.
Yes, we've done our homework and the results fit with everything we already felt. Newcastle disease is the number one threat to village chickens in Malawi so enabling communities to set up sustainable vaccination programs makes sense.
This is an amazing group of women in Mchinji District about 100 km to the west of Lilongwe. They already existed before we arrived on the scene but we can definitely make a difference and improve their likelihoods through our inputs.