The C.D.C. provides data at the national level for cases by age and sex and race/ethnicity, but not for both together at the state or county levels. We have asked the C.D.C. for such data but have been told by officials that they cannot share it. These breakdowns are essential to make sense of what is happening.

And now, because the government has not allowed outside access to all of its data, key questions are still unanswered nine months after the virus gained a foothold in the United States: Has coronavirus transmission really shifted to younger ages? Adjusting for age and comorbidities, has the death rate among Covid-19 patients improved because of better treatment? Have local mandates influenced the case rate or the hospital admission rate taking these other factors into account, and how?

I don’t know why the government is withholding some of the information it has gathered, when releasing it would so clearly be in the public interest. Perhaps it is driven by a concern that more data will lead to greater scrutiny and criticism over the handling of the pandemic, or misplaced concern that somehow anonymized tabulations of medical information could infringe on individuals’ privacy.