Meta deciding its best disinformation defense is to show no search results at all for a query as common as "covid" is something I would have expected to see as a parody in the Onion, not actual reporting in the Washington Post. https://www.washingtonpost.com/technology/2023/09/11/threads-covid-coronavirus-searches-blocked/
Threads blocks searches related to covid and vaccines as cases rise

Meta acknowledged that Threads is intentionally blocking the search terms.

The Washington Post
@robpegoraro I searched “Covid” in threads and it sent me to the CDC website. I’m in favor of that.