Over the last few decades, the recognition and impact of viral and rickettsial diseases have increased dramatically-especially following COVID-19, which was declared a pandemic by the World Health Organization (WHO) on March 11, 2020, with the end of the pandemic phase announced on May 5, 2023, by the organization. Emerging and re-emerging, clinically important viruses and rickettsial/tick-borne pathogens include those that have adapted to new environments because of travel and importation (eg, West Nile virus, chikungunya, mpox), climate change and expanded vector ranges (eg, dengue, Zika, Japanese encephalitis, tick-borne encephalitis viruses, Ehrlichia), and tightening of human-animal interfaces (eg, avian influenza, coronaviruses, Ebola, murine typhus). The most notable new viral pathogen to enter human populations was SARS-CoV-2, the causative agent of COVID-19. The global scientific community has responded to many of these threats by working together to develop new diagnostics, therapeutics, vaccines, and public health interventions, as well as to improve access to old ones.

For viral pathogens, novel immunotherapies have been successful against some (eg, CAR T-cell therapy for cytomegalovirus in immunocompromised patients), and novel and repurposed antiviral agents are now widely available for others (remdesivir, molnupiravir, nirmatrelvir/ritonavir for SARS-CoV-2). Novel vaccines and therapeutics have been recently developed for RSV for patients 60 years and older, pregnant women and neonates. In contrast, older, well-known viruses (eg, rabies, arboviruses, common cold coronaviruses) continue to cause extensive and sometimes severe disease in the absence of new therapeutic and preventive agents. Less attention has been paid to rickettsial diseases, although pathogens such as Rickettsia rickettsii and R typhi infect increasingly large swaths of the population. Perhaps as important as effective diagnostics, therapeutics, and vaccines, dedicated attention to environmental and climate issues is urgently needed to control and prevent diseases due to new, variant, and re-emerging viral and rickettsial pathogens. Our knowledge of these pathogens is advancing rapidly because of exciting technologic leaps in the fields of vaccinology, multiomics (proteomics, transcriptomics, genomics, metabolomics), and diagnostics.