Before revision:  Several plausible causes for this drop are examined , such as improvements in treatment , face mask wearing, a new virus strain, and potentially changing demographics of infected patients, but none are overwhelmingly convincing given the currently available evidence .
After revision:  Several plausible causes for this drop are examined , such as improvements in treatment , face mask wearing, a new virus strain, and age demographics of infected patients, but none are overwhelmingly convincing given the currently available evidence .