## 5 Current Licensed Vaccines for Viral Diseases
There are several patented vaccines against IHNV, including live-attenuated vaccines, inactivated and reverse genetic vaccines [123; 124; 125]. However, safety and environmental concerns have prevented commercial availability. APEX-IHN was commercially marketed due to its protective efficacy and reduction in transmission [126]. Currently, DNA vaccine trials are being conducted, the majority of which are developed based on the G protein unique to the IHNV U and M genotypes. Multivalent vaccines are being researched to combat both IHNV and VHSV [127]. Red Sea Bream Iridovirus (RSIV) is a single-stranded DNA virus belonging to the _Iridoviridae_ family and the _Megalocytivirus_ genus. It utilizes a horizontal mode of transmission and has been found to infect juveniles more than adults. There have been some trials attempting to develop a genetic vaccine and a recombinant yeast cell oral vaccine [128]. A formalin-based vaccine was developed by [PERSON] et al., 1999 [129]. While this vaccine is currently available for fish species of the _Seriola_ genus, it is not effective on rock bream [130]. Currently, there are trials being conducted to determine the efficacy of DNA vaccines and vaccines effective on rock bream [130; 131]. When conducting cross-examination against other Megalocytiviruses, AQUAVAC(r) IridoV showed partial protection against infectious spleen and kidney necrosis virus (ISKNV) and no cross-protection against scale drop disease virus (SDDV) [132]. As a result, a bivalent or polyvalent vaccine is being considered. One example is the PISCIVACT(tm) Irido Si vaccine, which specifically protects red sea bream against both RSIV and Streptococcus iniae, and is licensed in Japan [133]. Salmonid Alphavirus (SAV)  
The salmonid alphavirus itself is a positive-sense RNA virus belonging to the family _Toogaviridae_ and the genus _Alphavirus_. The diseases caused by the virus are pancreatic disease (PD) and sleeping disease (SD), and while both are classified as separate diseases, a histopathological study conducted found that both diseases are caused by a similar or identical agent. Additionally, both have similarities at the nucleotide and amino acid levels [134]. There are six different strains or subtypes of SAV. That being said, it was found that a vaccine containing a single subtype or strain can protect against PD caused by different strains of SAV, regardless of their subtype grouping [135]. Currently, only inactivated intraperitoneal vaccines are on the market. Though they are licensed for commercial use, it was found that Norvax Compact PD reduced the mortality rate by 50% [136]. Few studies have been conducted to evaluate the efficacy of all four vaccines. In a recent study, researchers compared the efficacy of two DNA vaccines, one based on a plasmid expressing the whole SAV structural polyprotein C-E3-E2-6K-E1 (pCSP) and one based on a plasmid encoding the SAV3 surface protein E2 alone (pE2), and Norvax Compact PD containing the inactivated SAV subtype 1 [137]. They found that pCSP and the Norvax vaccine reduced mortality rates, but when comparing all three vaccines, it was found that pCSP provided far more protection against the virus than Norvax and the p53 plasmid [137]. Thus, there is more research being carried out on developing a DNA vaccine against the virus. Recently, a DNA vaccine under the name of Clynav with SAV subtype 3 was approved by the European Medicine Agency and is currently undergoing commercial trials in salmon farms [138]. Infectious Pancreatic Necrosis Virus (IPNV)  
Infectious pancreatic necrosis virus is a double-stranded RNA (dsRNA) virus belonging to the _Birnavirus_ family. The virus affects salmonids, namely the rainbow trout and Atlantic salmon populations in North America and Europe. IPNV has a double-stranded genome, consisting of fragments A and B. Out of the five proteins that make up the virus, Fragment A is responsible for encoding VP2 and VP3, two major structural proteins of the virus. Specifically, VP2 proteins contain the most antigenic determinants [139].