The DPT vaccine provides protection against diphtheria, pertussis (whooping cough), and tetanus. It contains inactivated toxins from the causative bacteria, which stimulate the immune system to produce antibodies. This combination vaccine is essential in preventing three serious bacterial infections that cause respiratory illness, muscle spasms, and severe complications primarily in children. Neither BCG nor Hepatitis B or OPV vaccines target these diseases, making DPT the specific and effective choice for combined protection.

Reference: Harrison's Principles of Internal Medicine, J. Larry Jameson, 20th Edition.