**7. Vaccination and immune response toward** *H. pylori*

The trend of antibiotic resistance in *H. pylori* is increasing recently [1, 6, 10, 11]. Resistance rates for metronidazole, clarithromycin, and levofloxacin are the highest, surpassing 50%. This condition is worsening in previously treated subjects [25]. Besides, reinfection may occur even after the complete eradication of the previous infection [6]. This condition urges the development of a vaccine against *H. pylori* [1, 6, 10]. In the past decade, much effort has been devoted to the development of a vaccine as an alternative treatment for *H. pylori* infection [9]. There are two types of vaccine which are potentially possible: prophylactic vaccine and therapeutic vaccine. A therapeutic vaccine that can both eradicate infection and stimulate long-lasting immunity is the most desired one [10, 11]. Vaccine will significantly cut the economic burden from *H. pylori* infection even if the vaccine's efficacy is only 55% [2]. The first report on *H. pylori* vaccine development was submitted in 2011 by Moss et al., followed by Iankov et al. They conducted trials in mice and showed promising results. Cellular immunity, particularly Th1 response, is able to sterilize the microorganism [20]. The humoral immune response also gains the spotlight for the vaccine platform. The induction of Th2 response is proposed to be the basis of effective vaccination. A trial in mice showed high neutralizing specific salivary IgA and serum IgG after oral immunization. Besides preventing infection, the vaccine was also shown to have therapeutic properties. Gastric inflammation of mice in the trial was alleviated after vaccination [9]. In line with previous literature, Espinosa-Ramos conducted a vaccination trial in mice and observed that plasma secretory IgA and IgG are elevated post-vaccination. The presence of antibodies also protected 100% of mice in the study from virulent *H. pylori* [26]. The utilization of the vaccine seems promising, but this option still needs further development, especially in humans, considering the immune evasion ability of *H. pylori* [6, 9]. Public health intervention is still a major concern since preventing is better than treating the infection. Improvement in

socioeconomic status together with hygiene and sanitation may decrease the rate of infection as seen in developed countries [9].
