UK Pollster YouGov weighs in:

No, Boris Johnson catching coronavirus did not prompt a surge of support for the government. The surge had already taken place by 23 March - 4 days before the PM announced he had COVID-19 https://t.co/DHPyOsnm6f pic.twitter.com/BVkastVkET

— YouGov (@YouGov) October 2, 2020