The U.S. Government makes periodic releases of VAERS data. Each release is dated according to the latest report placed in the system, so if the release is dated March 2, that means it has all cases that have been entered into VAERS as of March 2.

The government releases data monthly, on the first Friday of the month. The date of this release is the previous week. For example, when they post data on June 6 it has data up to May 30, one week earlier. During COVID (and also back in 2010), the government did weekly releases of the data.

Medalerts.org updates the data as soon as the government releases it, usually within an hour of posting. If you look at the government's search engine, CDC Wonder, you will see the same date as MedAlerts. The two sites are in complete sync, because they are both fed from the government's data releases.