"In two days of polling before Trump got COVID, the president trailed Biden by just a 46-41% margin. In the three days of polling after the coronavirus diagnosis, Biden held a 55-34% lead. That means Biden’s lead grew by a whopping 16 points from pre-COVID to post-COVID."
Single day samples can be a bit noisy - the swing almost certainly wasn't that large but there is still a clear trend in recent polling that single day samples post COVID diagnosis tend to produce more favorable numbers for Biden.
