Rational approach to vaccination against highly pathogenic avian influenza in Nigeria: a scientific perspective and global best practice.

Since 2006, highly pathogenic avian influenza (HPAI) subtypes H5Nx have adversely affected poultry production in Nigeria. Successive waves of infections in the last two decades have raised concerns about the ability to contain infections by biosecurity alone, and evidence of recurrent outbreaks suggests a need for adoption of additional control measures such as vaccination. Although vaccination can be used to control virus spread and reduce the morbidity and mortality caused by HPAI, no country using vaccination alone as a control measure against HPAI has been able to eliminate or prevent re-infection. To inform policy in Nigeria, we examined the intricacies of HPAI vaccination, government regulations, and scientific data regarding what kind of vaccines can be used based on subtype, whether inactivated or live attenuated should be used, when to deliver vaccine either proactively or reactively, where to apply vaccination either in disease control zones, regionally, or nationally, and how to vaccinate the targeted poultry population for optimum success. A resurgence of HPAI outbreaks in Nigeria since 2018, after the country was declared free of the epidemic following the first outbreak in 2006, has led to enhanced intervention. Controlled vaccination entails monitoring the application of vaccines, the capacity to differentiate vaccinated from infected (DIVA) flocks, and assessing seroconversion or other immune correlates of protection. Concurrent surveillance for circulating avian influenza virus (AIV) and analyzing AIV isolates obtained via surveillance efforts for genetic and/or antigenic mismatch with vaccine strains are also important. Countries with high investment in commercial poultry farms like Nigeria may identify and zone territories where vaccines can be applied. This may include ring vaccination to control HPAI in areas or production systems at risk of infection. Before adoption of vaccination as an additional control measure on commercial poultry farms, two outcomes must be considered. First, vaccination is an admission of endemicity. Secondly, vaccinated flocks may no longer be made accessible to international poultry markets in accordance with WOAH trade regulations. Vaccination must therefore be approached with utmost caution and be guided by science-based evidence throughout the implementation strategy after thorough risk assessment. Influenza vaccine research, development, and controlled application in addition to biosecurity may be a precautionary measure in the evolving HPAI scenario in Nigeria.