I guess it's not clear to me how significant the deer "reservoir" issue is. If the virus is already common in the human population and humans are spreading to other humans, does the deer-to-human spread have a big impact? The notion that it could mutate in deer and be transmitted back to humans does concern me, but I'm not sure how much can be done about it? I'm not saying it isn't a problem, I'm just saying I don't have a handle on it.
That's a round about way of saying I didn't comment because I don't have anything particularly intelligent to say about it, as evidenced by the above.
The deer reservoir is significant because we can no longer harbor the (faint) hope that we can eliminate the SARS-CoV-2 virus. Even if 100% of the world's human population were fully immunized, the infected deer population would be large enough to endanger us.
Polio and smallpox are viruses that infect only humans and no other animal. With those viruses, if we vaccinate enough people, we can hope to eliminate those viruses. With smallpox, that may have actually happened. And with polio, that hope is still a possibility. If the white-tailed deer story holds up, SARS-CoV-2 will be around no matter how many people are vaccinated. Deer reservoirs of SARS-CoV-2 can provide a refuge for the virus outside of a largely immune/vaccinated human population and becomes a threat of virus re-emergence into humans.
In the paper, the authors took samples from 283 wild and captive deer in Iowa between 8 April 2020 and 6 January 2021 and ran PCR tests for the RNA from SARS-CoV-2 virus. The sampling period closely followed the course of the pandemic in Iowa. The first human case in Iowa was reported in 8 March 2020, with the peak in the 2nd week of November 2020.
That paper had a graph illustrating how the virus in deer closely follows the trajectory of the human pandemic during that time frame in Iowa. The blue bars (left axis) in the graph show the weekly Covid-19 cases per 100,000 humans, and the red line (right axis) shows the change in virus positive deer. (RPLN is the abbreviation for retropharyngeal lymph node, where they took samples from the deer.) This is much bigger than a few infected house pets or zoo animals.