To vaccinate or not against highly pathogenic avian influenza?
Authors: Krishna Prasad Acharya, Sarita Phuyal
Journal: The Lancet Microbe (2024)

The poultry sector is a major component of agriculture that contributes to the national economy and is crucial for food security, poverty reduction, and economic development.1Gržinić G Piotrowicz-Cieślak A Klimkowicz-Pawlas A et al.Intensive poultry farming: a review of the impact on the environment and human health.Sci Total Environ. 2023; 858160014Crossref PubMed Scopus (5) Google Scholar However, the poultry sector has been affected by poultry diseases, with highly pathogenic avian influenza (HPAI) having a serious economic impact on the sector. Avian influenza is a highly contagious poultry disease caused by orthomyxovirus,2Verhagen JH Fouchier RAM Lewis N Highly pathogenic avian influenza viruses at the wild–domestic bird interface in Europe: future directions for research and surveillance.Viruses. 2021; 13: 212Crossref PubMed Scopus (0) Google Scholar,3Causey D Edwards SV Ecology of avian influenza virus in birds.J Infect Dis. 2008; 197: S29-S33Crossref PubMed Scopus (0) Google Scholar which causes high mortality in poultry, leading to economic losses. HPAI results in the loss of billions of dollars in the poultry industry.4Mcleod A Morgan N Prakash A Hinrichs J FAOEconomic and social impacts of avian influenza.https://www.fao.org/3/ag035e/ag035e.pdfDate: 2005Date accessed: February 21, 2024Google Scholar In addition, from January, 2003 to February, 2024, 878 humans in 23 countries died owing to HPAI.5WHOHuman infection with avian influenza A(H5) viruses.https://cdn.who.int/media/docs/default-source/wpro---documents/emergency/surveillance/avian-influenza/ai_20240412.pdf?sfvrsn=5f006f99_129Date: 2024Date accessed: April 12, 2024Google Scholar Thus, HPAI is not only a poultry disease but also a public health concern. To reduce the damage caused by HPAI in low-income and middle-income countries such as Nepal, conventional preventive and control measures, including biosecurity measures, halting operations, culling, movement control, and quarantine, have been adopted. However, the disease has not been effectively controlled; instead, the incidence of HPAI has increased in recent years.6Wade D Ashton-Butt A Scott G et al.High pathogenicity avian influenza: targeted active surveillance of wild birds to enable early detection of emerging disease threats.Epidemiol Infect. 2022; 151: e15Crossref PubMed Scopus (6) Google Scholar Moreover, the use of conventional methods of control, halting operations, and culling have resulted in heavy economic burdens on poultry farmers, long-lasting impact on the livelihood of farmers, and welfare and environmental concerns,7WOAHAvian influenza vaccination: why it should not be a barrier to safe trade.https://www.woah.org/en/avian-influenza-vaccination-why-it-should-not-be-a-barrier-to-safe-trade/Date: 2023Date accessed: March 23, 2024Google Scholar which have led to the search for alternative methods such as vaccination to control HPAI and improve the economic sustainability of the poultry sector. Research from field trials in Bangladesh has shown that vaccination is effective against HPAI and reduces the incidence of infection and shedding of viruses from infected birds, thereby reducing the risk of transmission to other poultry and humans and the risk of spillover to wild animals. Some countries such as China, the USA, Egypt, Mexico, Viet Nam, and Bangladesh have used vaccines against HPAI and have reduced the incidence of HPAI.8Islam A Munro S Hassan MM Epstein JH Klaassen M The role of vaccination and environmental factors on outbreaks of high pathogenicity avian influenza H5N1 in Bangladesh.One Heal. 2023; 17100655Google Scholar, 9Nielsen SS et al.EFSA Panel on Animal Health and Animal Welfare (AHAW)European Union Reference Laboratory for Avian InfluenzaVaccination of poultry against highly pathogenic avian influenza – part 1. Available vaccines and vaccination strategies.EFSA J. 2023; 21e08271Google Scholar, 10Guyonnet V Peters AR Are current avian influenza vaccines a solution for smallholder poultry farmers?.Gates Open Res. 2020; 4: 122Crossref PubMed Scopus (13) Google Scholar However, vaccination against HPAI might lead to the development of new pandemic virus strains through recombination and genetic assortment, hide subclinical infections, and hinder the identification of field strains by surveillance. Despite the promising effects of vaccination against HPAI, many countries such as the UK and Brazil are reluctant to vaccinate their poultry because of the fear of international trade restrictions. Thus, the World Organization for Animal Health (WOAH) has suggested possibilities for using vaccines and has asserted that international trade should not be restricted if vaccination against HPAI has been conducted according to guidelines specified by the WOAH and comprehensive surveillance supports the absence of infection.7WOAHAvian influenza vaccination: why it should not be a barrier to safe trade.https://www.woah.org/en/avian-influenza-vaccination-why-it-should-not-be-a-barrier-to-safe-trade/Date: 2023Date accessed: March 23, 2024Google Scholar Although vaccination has been recommended by the WOAH as a control measure against HPAI, vaccines should be cautiously administered to ensure that they match well with circulating field strains, the vaccination programme is effective, and no recombination occurs between vaccine and field strains, leading to the development of more virulent HPAI strains. Furthermore, vaccination should not be used as the sole strategy to control HPAI; rather, vaccination should be used as a component of an HPAI control strategy to reduce HPAI incidence to levels that can be controlled using conventional methods rather than vaccination. In addition, clearcut strategies should be developed to identify subclinical infections that can be hidden by HPAI vaccination and detect circulating strains in field conditions. While advocating vaccination against HPAI, a cost–benefit analysis of vaccinating and non-vaccinating poultry should be conducted, and vaccination should be advocated if the benefits are greater than the costs. Thus, each country should evaluate the cost–benefit of vaccinating and not vaccinating poultry and accordingly decide whether to vaccinate their poultry against HPAI. Furthermore, a comprehensive study is needed to understand the epidemiology and transmission dynamics in each country, understand circulating viral strains in field conditions, update vaccine candidates to better match circulating field strains, and ensure that virulent strains of viruses have not evolved because of recombination and genetic assortment between field and vaccine strains. In our view, countries can vaccinate poultry to protect the birds from HPAI. However, thorough and comprehensive surveillance to track circulating strains of the virus, risk assessment of the development of recombinant highly virulent strains of the virus, and sound vaccination monitoring systems and evidence-based knowledge generation systems are needed to ensure the effectiveness of vaccination programmes, prevent the circulation of HPAI virus in avian species, and mitigate the risk of HPAI virus transmission through international trade. Thus, vaccination should not be used as a sole measure to control HPAI but should be used as part of a comprehensive disease control strategy. Successful prevention and control of HPAI requires a regional multidisciplinary coordinated One Health approach that includes strengthening of surveillance and monitoring systems, early warning systems, risk assessments, and timely dissemination of information to the general public and WOAH member countries. The vaccination system should better guarantee for human, physical, and financial resources and improve diagnostic capabilities and early warning systems. Moreover, each member country that uses vaccinations should share information related to the effectiveness of vaccination programmes and their surveillance systems in a timely manner to inform the development and implementation of HPAI control strategies. The authors declare no conflict of interest. Both authors contributed equally.