Optimizing Immunogenicity of an Inactivated Egg Drop Syndrome Vaccine: The Journey from Virus Isolation to Enhanced Seroconversion

Egg drop syndrome 1976 (EDS-76) was first identified in Egypt in 1991 and is notorious for causing sudden drops in egg production and quality, and Egypt’s flocks have felt its impact for decades. To address this, we isolated a local strain and set out to turn it into a safe, effective vaccine. We propagated the virus in 11-day-old duck eggs, where it flourished, reaching hemagglutination titers of 15 log 2 and infectivity of 8.1 log 10 EID 50 /mL after just four passages. We then confirmed its identity with a simple PCR test and sequenced its major coat protein gene, finding it almost identical (≥ 99.5 %) to both recent Egyptian field strains and the classic Netherlands vaccine strain, with no changes in the key antigenic domains of the virus surface molecule targeted by the immune system of the bird. Next, we inactivated the virus using just 0.2 % formalin for 48 hours—enough to render it harmless but gentle enough to keep its key antigens intact at 14 log 2 HA activity. We mixed this inactivated virus into five oil-based emulsions (250–2 000 HAU per dose) and confirmed each batch was stable, sterile, and ready for scale-up. Finally, we vaccinated SPF White Leghorn chickens, where 100 % of them seroconverted by Week 2. The highest-dose group (2000 HAU) developed average HI antibody levels of 13.5 ± 0.6 log 2 and neutralizing antibodies of 12.0 ± 0.5 log 2 by Week 4, outpacing a leading commercial vaccine. A tight correlation (R 2 = 0.98) between HI and neutralization tests means we can reliably track protection with the simpler HI assay. Together, these results show that EDS-76 is not just a promising candidate but an ideal seed strain for an inactivated EDSV vaccine: it’s safe, easy to make in large quantities, and elicits strong, lasting immunity. Supplementary Material File (mnuscript.docx) - Download - 118.60 KB Information & Authors Information Version history Copyright This work is licensed under a Non Exclusive No Reuse License.

Authors Metrics & Citations Metrics Article Usage 190views 121downloads Citations Download citation Mahmoud Ali, Mayar A. El-Nagar, Mohamed N. F. Shaheen, et al. Optimizing Immunogenicity of an Inactivated Egg Drop Syndrome Vaccine: The Journey from Virus Isolation to Enhanced Seroconversion. Authorea. 08 October 2025. DOI: https://doi.org/10.22541/au.175992872.22991986/v1 DOI: https://doi.org/10.22541/au.175992872.22991986/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu.