We thank the reviewer for the additional comments and reply point by point below.

1. For clarity the title should probably say "against infected birds" rather than "of infected birds"
	> We changed the title as suggested
2. Table 2 - where no birds ever co-infected with both J and K? Given your numbers (particularly at early ages) that seems unlikely? (totals in the ratio column always add up to number infected)
	> We did not see co-infections in this experiment. Lack of double infections is not that unlikely. For example, for the B7 Plymouth Rock line on day 140 (where the overall infection prevalence is highest), the prevalence of single infection is 0.5% (K) and 13.5% (J). Assuming independent infection, expected double-infection frequency is roughly 0.005 * 0.135 = 0.0007. This implies 0.0007*966 = 0.65 < 1 birds expected to be infected by both viruses. 
3. Figure 1 - a schematic is very welcome, but 1A doesn't really show anything. It would be much better to present to-scale schematics for both ALV-J and -K showing where all primers go across the elements. This would allow you to address where the conserved regions are between subgroups, and where the unique regions are that you have targeted.
4. Figure 1 - similarly, inclusion of B is good but the low resolution graph and vague supporting text means you don't take much from the graph. Which lines specifically are the negative controls? Where is your cut-off for non-specific targeting? Did you check those with lowest fluorescence for homology with desired target?
	> See the new Figure 1. We believe we addressed all these suggestions.
5. Figure 2 - as flock sizes differ (slightly), % infected would be more informative, with some way of indicating the difference in drop-off rate for K and J. As you are describing the flock as a whole, you could use line graphs (with separate lines for each flock, and for K/J). Anything to improve the clarity. Similarly, a 6 word figure legend is not sufficient for understanding the graph in isolation.
	> See the new Figure 2. We implemented the changes the reviewer suggests.