Dengue infection is a zoonotic disease caused by Dengue virus, a single-strand RNA flavivirus. It is transmitted to humans through primarily Aedes aegypti (mosquito) bites. The disease prevalence is higher in tropical zones where there are high humidity and temperature as well as unplanned urbanization. According to the WHO, more than 100 tropical countries are afflicted by Dengue infection, leading to severe economic impact. Brazil is currently a major hotspot of Dengue infection. The number of infected people with dengue virus increased 240% in the first trimester of 2015 compared to the same period last year, surpassing the WHO estimative. In an attempt to stop the infection from spreading, the Brazilian Health Ministry has increased the budget to nearly $50 million to combat the vector. However, the bureaucracy of the Brazilian government has led to slow release of the allocated money to the affected cities and the results have been catastrophic. To make the situation worse, the slow diagnosis and the subsequent delay in starting the treatment has led to increased mortality rates. Currently, the only treatment available for Dengue infection is supportive, which is not very efficient against the most severe cases such as Dengue Hemorrhagic Fever (DHF) or Dengue Shock Syndrome (DSS).

The interruption of centuries of decline in case rates of Tuberculosis (TB) occurred, in most cases, in the late 1980s and involved industrialized countries due to increased poverty in urban settings and the immigration from TB high-burden countries. Thus, no sustainable control of TB epidemics can be reached in any setting without properly addressing the global epidemic.

A considerable rate of deaths from TB has been attributed to co-infection with Mycobacterium tuberculosis and Human Immunodeficiency Virus (TB-HIV). Immune deficient patients with HIV are at increased risk of latent M. tuberculosis infections (LTBI) progressing to active disease and being transmitted to others represents a considerable reservoir of bacilli. In addition, more than a half of the new TB cases are potentially MDR-TB “super strains” in the hot zones, such as the “BRICS” countries (Brazil, the Russian Federation, India, China and South Africa). MDR-TB strains, an airborne bacterium that is spread just as easily as drug-sensitive TB, are resistant to at least three of the four main drugs used to treat TB. Likewise, it has been reported the emergence of extensively drug-resistant (XDR) TB cases, defined as cases in persons with TB whose isolates are resistant to isoniazid and rifampicin (MDR-TB) as well as resistant to any one of the fluoroquinolone drugs and to at least one of the three injectable second-line drugs, Amikacin, Kanamycin or Capreomycin. XDR-TB is widespread raising the prospect of virtually incurable TB worldwide, such as the novel Total Drug-Resistant (TDR) TB strains found in India, Italy and Iran. The factors that most influence the emergence of drug-resistant strains include inappropriate treatment regimens, and patient noncompliance in completing the prescribed courses of therapy due to the lengthy standard “short-course” treatment or when the side effects become unbearable.

Recently, I attended the Modern Vaccines Adjuvants and Delivery Systems conference held in Leiden, The Netherlands (May 18-20, 2015); which highlighted some of the major challenges in the development of efficacious vaccines and their effective delivery for both (re) emerging infectious diseases and endemic Neglected Tropical Diseases (NTDs). These infections include not only the “big three” of Malaria, HIV/AIDS and Tuberculosis, but also Leishmaniasis, Ebola, MERSCOV, helminths and others. Notably, for the “big three” attempts to develop such vaccines have been largely disappointing. Some of the challenges lie with the extreme genetic variability of the pathogens. Most successful vaccines have been against slowly evolving pathogens with a limited number of antigenically different strains that induce immune responses dependent on neutralizing antibodies; a mechanism that is well understood. Also, for most vaccine preventable diseases, natural infections with their pathogens leave the host (temporarily, partially) immune to reinfection or disease with the same (strain of) pathogen. The danger of these pathogens is that they often win the race between their own rapid rate of multiplication and the host response which depends on immune recognition and activation and proliferation of immune cells, specifically-B cells. Once the host mounted an immune response and survived the fight he has won the race. Most of the infections above, however, do not conform to that pattern. In TB, cellular mechanisms are essential for controlling the infection, but do not eliminate it. The pathogens, Mycobacterium tuberculosis (Mtb), reproduce very slowly and disease occurs, if at all (in a minority of infections), months or years after infection. Disease, once cured, does not offer protection against reinfection or disease from reinfection. Speed of immune recognition seems to play no role, as most individuals who develop TB have detectable (by IGRA or TST) immune responses to the pathogens. Rather, it seems, a failure of the cellular effector mechanisms is at fault, and if so the prospects for an effective vaccine that protect against disease are slim. As neutralizing antibodies play no role in protection, also the prospects of conferring protection against (re) infection seem equally poor. Immune mechanisms against malaria and HIV are also complex and poorly understood, and attempts to develop an HIV vaccine have been graphically called “shots in the dark” [1]. The more I learn about vaccines and vaccination, the more I become perplexed, less optimistic, but also fascinated. Despite the stunning recent advances in immunology and medical research why do we still fail, and what are the missing scientific links? Are vaccines for some infections simply impossible, or are we simply not aiming our efforts correctly? Progress seems increasingly difficult, but the rewards of success, therefore so huge. The English physician Edward Jenner developed (or rather discovered) that cowpox offered a relatively safe alternative to the risky practice of variation in 1796 and in 1977 smallpox was eradicated worldwide. On May 8, 1980, the World Health Assembly announced that the world was free of smallpox and recommended that all countries cease vaccination: “The world and all its people have won freedom from smallpox, which was the most devastating disease sweeping in epidemic form through many countries since earliest times, leaving death, blindness and disfigurement in its wake” [2]. Jenner just observed, but knew nothing about viruses, let alone immunology.

The Eastern Mediterranean region has set goals for interrupting indigenous transmission of measles using a strategy developed by the World Health Organization. This strategy includes recommendations for vaccination activities to be achieved and sustained thereby increasing the population’s immunity. Measles epidemiological surveillance systems were developed to monitor illnesses characterized by febrile rash, and to provide effective virus detection and serological surveillance. Elimination is defined as the absence of endemic measles transmission in a defined geographical area (e.g., region or country) for ≥12 months in the presence of a well-performing surveillance system. Oman has committed to these goals.

Measles was a leading cause of infant and child morbidity and mortality in Oman before the introduction of measles vaccine by 1975 and thereafter until 1994. With the introduction of a second dose of measles vaccine in 1994, coverage for first and second doses of measles vaccine increased more than 95% in 1996 and has been sustained at a level greater than >95% since then. A national Measles and Rubella (MR) immunization catch-up campaign targeting children ages 15 months to 18 years was conducted in 1994 that achieved 94% coverage. As a result, the incidence of measles has declined markedly in recent years, to ≤ 1 case per million persons in 2012 and to zero cases in 2013.

Oman has made significant progress toward measles elimination and has met the regional elimination goals. However, new challenges faced by Oman, for instance with increased globalization, has led to issues such as outbreaks from imported cases. Additional challenges still remain with regard to increasing identification and immunization of unvaccinated non-Omani workers and their families.

Our research focused on Avian Influenza Type A-H5N1, specifically on an epidemiological model centered in Puerto Rico. Our main goal is to address the following: first, to determine the potential outbreaks of this disease in Puerto Rico using as a base the location of the poultry industry as a hub, we are interested in the repercussions of the infection among the human-to-human potential interaction. The second goal centers on the possibility of vaccination to mitigate an epidemic among humans. In order to address these goals and future ones, we will construct a mathematical model and use parameters according to two cases; the first is a single population model and the second one is a metapopulation model involving 5 cities in Puerto Rico. Our research will specifically target the spread of this particular disease, to investigate possible alternatives to mitigate the spread using measures of immunization. Our results show that a 30% vaccination regime will eradicate the disease in cities that are immunized.