The Hammers are out of the bottom three on goal difference only but the clash with the struggling Black Cats gives them the opportunity to go eight points clear of the Premier League's bottom club.
Jarvis has admitted the pressure is now on the team going into the hectic festive period but he remains confident.
"Saturday is a vital game and we need to keep working extremely hard, be positive and make sure we get that result," he said.
"The pressure is always on the team, but we need to stand up and be counted. We don't need to worry about what Sunderland are doing, we need to get back to winning ways and climb up the table."