Hey Lianne,
Sadly there is no way of preventing other people's Out of Office notifications from sending. Instead, i would recommend creating an inbox rule to route all Out of Office emails into a folder or to just delete them. Since Out of Office emails tend to contain the subject of the original email you could update the rule every time, or focus on the email content to filter.
When you recieve an Out of Office from a lead though, it is actually a pretty good thing! With the Out of Office you know that the email is valid without really engaging the person. Also, depeding on how much time you have, you can go through the OOO messages and get more data about them.
If your email address is used as the "reply-to", I would also think about your personal Out of Office email and settings. If someone else sends out an email with you as "reply-to" and people reply the same day, may be weird to get an OOO message. The Out of Office settings (in Outlook 2011 at least) are pretty weak as you are limited to filtering on your company or contact list. With some help from your IT team though, it may be possible to update the email server's OOA settings.
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