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June 2012: The VAERS Wayback Machine

Every month, the government releases new VAERS data. At first glance, it would appear that each release is just the old data, plus those new reports that have been added during the month.

But a government VAERS release is actually much more.

Each month's release is a complete dump of the entire VAERS database, going all the way back to the start of the program in 1990. This is because the government never closes a VAERS report, and may make changes to any report at any time. They can even remove a VAERS report.

So who is watching this data, making sure that the changes are sensible or correct? In the past, it was the NVIC - now you can do it too!

This blog entry introduces a new feature in MedAlerts: the VAERS Wayback Machine, a collection of old VAERS releases that can be analyzed to help understand the changes being made each month. The NVIC has been using the Wayback Machine internally for a few years, and now it is part of the MedAlerts website.

First, some background. When you search the VAERS data at MedAlerts (or even at CDC Wonder) you are looking at the latest release of the government data. The date of that release is shown at the top of the search form:

When the month is over, that data will no longer be searchable, because the next month's release will be available. But the data isn't really gone, because MedAlerts has been saving the data since 2003.

The Wayback Machine lets you do three different things with the data.

  1. Search an old release of the data.
  2. Compare two releases of the data to see what is changed.
  3. Track all changes to a single VAERS report.

Search an old release of the data

The Wayback Machine lets you choose an older version of the data, and then do a standard MedAlerts search on it. When searching old data, both the search form and the search results inform you that you are working with old data, so that there is no confusion. Here is what you see when you search the oldest release of the VAERS data available in MedAlerts:

Compare two releases of the data

The Wayback Machine lets you choose two different releases of the VAERS data and compare them. You can do an Added/Deleted comparison or a Changed comparison. Note that these searches, which compare two entire VAERS releases, can take a long time to complete, so be patient when asking for them.

The Added/Deleted comparison lists the VAERS ID numbers for reports that were added or deleted. These reports are characterized according to whether they are Minor, Serious, or Death-related (See an earlier blog for more on "serious"). It also analyzes the death-related reports and lists the vaccines found there. Note that all of the VAERS ID numbers are links which show the full event details (even for deleted reports). Here is a sample comparison between the June 13, 2012 and the July 13, 2012 releases (abbreviated to save space):

The Changed comparison looks at those reports that were in both releases, and shows changes that were made to them. Changes are color-coded so you can tell what is different. Anything printed in Red is something that was in the older release, but not in the newer one (so red means something that was removed). Anything printed in Green is something that is in the newer release, but was not in the older one (so green means something that was added). Because this can be a large amount of data, this Changed comparison stops after 400 changed reports.

Here is an example of a ficticious change report in which the date of vaccination and onset has changed, the manufacturer of the Flu vaccine has changed, the number of days in the hospital was entered (was previously blank), four symptoms have been removed, and the write-up and preexisting conditions were edited:

Track all changes to a VAERS report

If you know the VAERS ID of a particular report, you can give it to the Wayback Machine and see the complete history of that report, going all the way back, and including all changes made since 2003. Once again, reports are color-coded so you can tell what has changed.

Note also, that when MedAlerts gives you an Event Detail report, there is a little button that offers this historical tracking:

What has been learned from the Wayback Machine?

Here are just a few of the things that have been discovered by the VAERS Wayback Machine:

But there is probably much more to be found, so if you are a hard-core VAERS data follower, the Wayback Machine is the website for you!

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