Recent (in the last 10 years) work looking at heat stress and optimizing response to BRD vaccines have brought the 85/70 rule of thumb to the forefront.
If daytime temps are above 85, and it doesn't cool down to at least 70 degrees for at least 4 hours at night... you don't need to be doing ANYTHING with cattle. Working cows in conditions above the 85/70 point can result in dead cattle - and even if you don't kill 'em, the likelihood that they're gonna respond favorably, if at all, to any vaccinations administered is pretty poor.
I'd needed to palpate my spring-calving cows, start pre-weaning vaccs. on the spring calves, and castrate/vaccinate some of the calves born in the past month this past weekend - but with the current heat/humidity conditions, I wasn't gonna risk it. Will just rotate 'em another time around the farm, and hope it's cooler when they come back around in 3 wks.