Safe SQL query in PHP

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";

try {
  $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
  // set the PDO error mode to exception
  $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

  // prepare sql and bind parameters
  $stmt = $conn->prepare("INSERT INTO MyGuests (firstname, lastname, email)
  VALUES (:firstname, :lastname, :email)");
  $stmt->bindParam(':firstname', $firstname);
  $stmt->bindParam(':lastname', $lastname);
  $stmt->bindParam(':email', $email);

  // insert a row
  $firstname = "John";
  $lastname = "Doe";
  $email = "[email protected]";
  $stmt->execute();

  // insert another row
  $firstname = "Mary";
  $lastname = "Moe";
  $email = "[email protected]";
  $stmt->execute();

  // insert another row
  $firstname = "Julie";
  $lastname = "Dooley";
  $email = "[email protected]";
  $stmt->execute();

  echo "New records created successfully";
} catch(PDOException $e) {
  echo "Error: " . $e->getMessage();
}
$conn = null;
?>