Dr. Gessner is a pediatrician and medical epidemiologist who received his medical training at the Universities of Florida and Colorado, followed by an EIS Fellowship with the US CDC, and an MPH and Preventive Medicine Residency at the University of Washington. He started and developed the Maternal-Child Health Epidemiology Unit within the Alaska Division of Public Health focused on infectious diseases, outbreaks, infant mortality, child abuse, and birth defects. He joined Agence de Medecine Preventive, a 90 person NGO based in Paris, France and several African countries that focused on post-licensure vaccinology primarily in resource-poor settings. During his tenure as the Scientific Director and Chief Scientific Officer, AMP grew by almost 10-fold in resources and doubled its permanent staff. His work spanned most aspects of field vaccinology including large scale clinical trials, vaccine efficacy and effectiveness, surveillance, laboratory innovations, immunogenicity, carriage, economics, logistics, implementation, and training. He worked on many currently available vaccines including pneumococcal, meningococcal and Hib conjugates and plain polysaccharides; OPV and IPV; rotavirus; RTSS malaria vaccine; dengue vaccine; HPV; and pertussis whole cell and acellular.

From December 2016 through March 2025, Dr. Gessner served as Vice President and Global Medical Lead initially for Pneumococcal Vaccines to which he added vaccines for Lyme, Group B Streptococcus, SARS-CoV-2, Respiratory Syncytial Virus (RSV), Parainfluenza virus (PIV), and human Metapneumovirus (hMPV). From approximately 2023 till his departure, he served as Vice President and Global Medical Lead for Respiratory Vaccines and Antivirals, which included PCV13, PCV20, and next generation PCVs; RSV for maternal and older adult indications; respiratory combination vaccines that included PIV and hMPV; and RSV antivirals. In this role he was responsible for medical affairs activities related to four product launches (PCV20 pediatric and older adult; RSV maternal and older adult) including regulatory documents and interactions with regulatory agencies, vaccine technical committee interactions and dossiers, establishing Pfizer’s scientific positions for internal colleagues (medical and commercial) and external communication, overseeing KOL engagements, addressing safety concerns, reviewing commercial positions, and other activities as needed. In addition, he oversaw all post-licensure studies (almost all designed as research collaborations) needed to meet regulatory commitments, expand product labels, generate recommendations, inform the value proposition for vaccines, or improve uptake. At his hire in 2016, he supervised a group of five professionals and at his departure he supervised a team of 35 PhD and MD scientists and medical experts.

Dr. Gessner is the author of approximately 480 peer-reviewed publications from over 40 countries, as well as an author for hundreds of presentations at scientific congresses, book chapters, and technical reports and maintains a faculty appointment at the University of Maryland’s Center for Vaccine Development. He has served on the Gavi Board and Gavi Program and Policy Committee; WHO’s IVIR-AC and IPAC committees (that directly advise SAGE); WHO SAGE working groups; and numerous advisory groups for WHO, the Bill & Melinda Gates Foundation, and industry. Currently, Dr. Gessner is the Sole Proprietor of EpiVac Consulting,