76 Emerging and Reemerging Diseases

The emergence and reemergence of infectious diseases pose unprecedented challenges to global public health (Emerging and Reemerging Infectious Diseases 2016). These diseases can have devastating impacts and in particular when they are fast-spreading, they affect a large number of people, this is where the disease impacts most people at one time. When diseases are regarded as emerging ones, this means that they have only just appeared or have suddenly intensified and increased to such an extent that their incidence or range are expanding rapidly going on. On the other hand, reemerging diseases were originally under control but because of a wide variety of factors such as those in society, changes to the environment and reductions in immunity these diseases have returned once more to society. The reemergence of these diseases often represents weaknesses that exist in health systems and society, particularly when risk factors are changing and public health measures disrupt (Emerging and Reemerging Infectious Diseases 2016). (E.B.)

Measles is a prime example of a reemerging disease. Although it was formerly considered as eradicated due to significant success in vaccination programs against it, measles has made quite a comeback in recent years. The US Centers of Disease Control and Prevention says that in 2025 there were 378 confirmed cases of measles, a significant increase from previous years (Centers for Disease Control and Prevention 2025). This resurgence in measles is most likely caused by declining vaccination rates, which is often influenced by misinformation and vaccine hesitancy, which has resulted in a large population of unvaccinated communities. The disease thrives better in places where vaccination coverage has slipped just below critical levels necessary for herd immunity (Centers for Disease Control and Prevention 2025). (E.B.)

For a long time, vaccination has been one of the most effective ways to prevent measles, because the measles vaccine has a very high rate of efficacy. However, if vaccine coverage falls below the threshold needed to avoid outbreaks, i.e. around 95% according to CDC figures on measles spread in America then it becomes likely that this disease will start spreading rapidly once more (Centers for Disease Control and Prevention 2025). Measles outbreaks in the United States are usually associated with areas or communities where vaccination rates are low, especially among certain groups who refuse vaccines because of misinformation or mistrust of healthcare systems. In addition, like global travel which enables the virus to cross borders, further contributes to re-emergence of measles in formerly controlled areas (Centers for Disease Control and Prevention 2025). (E.B.)

The reemergence of measles also poses a significant public health threat, particularly to vulnerable populations. Infants too young to be vaccinated, people who are immunocompromised and those who are under-vaccinated are at higher risk for serious complications from measles. Complications can be severe, including pneumonia, brain inflammation (encephalitis) and death, especially children under five. This underscores the need for strong surveillance systems for early outbreak detection and prompt public health responses (World Health Organization 2023). It also stresses the need to reach and sustain high coverage of vaccination, to protect the most vulnerable. (E.B.)

Factors connected to human behavior, public health policies, environmental change and global interconnectedness all play a role in emerging and reemerging diseases like measles. Like measles, a decrease in vaccinations from misinformation and vaccine hesitancy is a major cause of the disease’s resurgence. International travel and migration can contribute to the spread of pathogenic diseases, as people cross national borders, bringing pathogen strains to geographic areas where they were previously managed (World Health Organization 2023). This is why it’s even more critical that public health organizations keep an eye, use all the big data we learned from COVID surveillance systems to track disease patterns, and educate the public on the importance of vaccination (World Health Organization 2023). (E.B.)