Assessment of the in-use stability of the PRRS virus of two different commercial PRRS MLV after reconstitution with PPV and SE vaccines

Nowadays, many vaccination programs have to be implemented in sows. Firstly, reduction of injections by administering vaccines simultaneously can improve both animal welfare and the farmer’s labour efficiency. Secondly, these combinations must be safe and effective, the European Medicines Agency (EMA) being the institution responsible for guaranteeing the efficacy of these mixtures. The purpose of this study was to assess the inuse stability of the UNISTRAIN® PRRS vaccine after it has been reconstituted with ERYSENG® PARVO in comparison with the in-use stability of another European commercial PRRS MLV reconstituted with the SE and PPV vaccine from the same manufacturer.

A freeze-dried tablet of 25 doses of UNISTRAIN® PRRS was reconstituted with 50 ml of ERYSENG® PARVO (group A) and a freeze-dried tablet of a European commercial MLV vaccine was reconstituted with 50 ml of the SE and PPV vaccine from the same manufacturer (group B). A freeze-dried tablet of the same batch of UNISTRAIN® PRRS was reconstituted with 50 ml of its solvent (group C) and a freeze-dried table of the same batch of a European commercial PRRS MLV was reconstituted with 50 ml of its adjuvant (group D). Group C and D were used as controls. The titre of the PRRS virus from the different mixed vaccines was assessed at T = 0, 1, 2, 3 and 4 hours after reconstitution and they were kept at room temperature until the end of the study. The virus was titered by measuring its cytopathic effect in the MARC 145 cell line. According to the SPC for each of the products, the minimum cell culture infection dose (MCCID) of UNISTRAIN® PRRS is 10^3.5 CCID₅₀ and for the other European commercial MLV vaccine it is 10⁴ CCID₅₀.

The results showed that in group A, the PRRS virus remained stable for 2 hours after the reconstitution. From 2 hours onwards, the virus titre started to decline but remained above the MCCID until the end of the study. In group B, an important drop in the PRRS virus titre was observed less than 1 hour after reconstitution and led to results clearly below the MCCID (10⁴ CCID₅₀/dose). In the control groups for both vaccines, the PRRS virus remained above the MCCID until the end of the study.

The most important factor involved in keeping the registration of the combined use of an MLV PRRS vaccine and SE and PPV vaccine is to ensure that the PRRS virus is kept alive after they are mixed together. These results conclude that the viability of the PRRS virus after mixing UNISTRAIN® PRRS and ERYSENG® PARVO can be guaranteed for 2 hours after reconstitution.

Disclosure of Interest: None Declared.