A "Seed Virus" is the culture of virus used to start a culture. Seed means to inoculate. And a "Seed" culture is the first culture used to start stock cultures.
So if you were going to start a stock culture of virus for vaccine development, you would first inoculate your culture with a seed virus.
Refer to the abstract of this paper for context...
Newcastle disease virus strain I2 a prospective thermostable vaccine for use in developing countriesForty-five avirulent Australian strains of Newcastle disease virus had been examined for antigenicity in chickens and 18 of these were tested for thermostability. Strain I2, chosen for a combination of antigenicity and thermostability, was artificially selected for enhanced thermostability.
Master seed material was then prepared in minimal disease eggs, and vaccine by a further two passages in conventional eggs. Strain I2 virus at seed and vaccine level induced adequate levels of antibody in chickens vaccinated by eye drop and usually in their contacts. The serological response to oral vaccination was less certain.
Antibody titres indicative of substantial protection against virulent challenge were maintained in a simulated village flock for 38 weeks by vaccination of the foundation flock on two occasions, with subsequent vaccination confined to clutches of chicks as they were produced. Strain I2 virus survived for at least 12 weeks when stored at 22°C in 1% gelatin. Strain I2 is suitable for local production of thermostable vaccine in regional laboratories in developing countries.
Also look at...
Dengue-Virus Recovery by Direct and Delayed Plaques in LLC-MK2 CellsA method for detecting and propagating dengue viruses in LLC-MK2 cells has been developed by direct plaquing and by fluid maintenance of inoculated cultures 7 to 14 days before plaquing (delayed plaquing). This procedure was used in support of studies of hemorrhagic fever and has resulted in the recovery of 69 dengue viruses, including all four serotypes. About half of these were detected by delayed plaques when direct plaques were not seen. Most of these dengue strains were inoculated simultaneously into mice and cell cultures. The direct and delayed plaque method was more sensitive and efficient than the use of suckling mice. Comparisons of the direct and delayed plaque method with other methods of recovery of dengue virus are discussed.
Early in the study, occasional difficulty in preparing low-passage cell-culture seed virus of adequate titer was encountered. Consequently, the growth of dengue virus in LLC-MK2 cells was studied. Virus growth was synchronous and cyclic. In order to avoid inadvertent harvesting of virus during eclipse, live cells, rather than cell lysates, were passaged. This has resulted in consistent production of low-passage seed-virus suspensions.Hope this helps...