# Efficacy of PCV2 Vaccination Under Natural Conditions: A Longitudinal Study Using PCR and Virus Isolation

## TL;DR

This study shows that PCV2 vaccination reduces infection and disease effects in pigs, but PCR alone isn't enough to measure vaccine success.

## Contribution

The study demonstrates that virus isolation is necessary alongside PCR to accurately assess PCV2 vaccine efficacy in real-world conditions.

## Key findings

- Vaccinated pigs showed no PCV2 virus isolation, while 50% of unvaccinated pigs did.
- PCV2 gene load was significantly lower in vaccinated pigs at 91 days.
- PRRSV infection may enhance PCV2 replication, as it was detected before PCV2 gene load increased.

## Abstract

Porcine circovirus type 2 (PCV2) causes porcine circovirus-associated disease. This study assessed the efficacy of the PCV2 vaccine (Ingelvac CircoFLEX®) under natural conditions, including age, evaluation methods, and co-infection in piglets on farms. One hundred serum samples were collected from vaccinated and unvaccinated piglets. PCR and antibody positivity rates were similar in both groups. These results suggest that qPCR detection of PCV2 genes in blood alone is insufficient to assess vaccine effectiveness, and additional methods, such as virus isolation, are needed. Porcine reproductive and respiratory syndrome virus (PRRSV) infection, observed at a low level on day 63 before PCV2 infection at 91 days, may be involved in PCV2 replication. This study found that vaccination against PCV2 efficiently reduced the negative effects of PCV2 replication and effectively controlled PCV2 infection under field conditions.

Porcine circovirus type 2 (PCV2) is the main cause of porcine circovirus-associated disease (PCVAD). Despite the widespread use of anti-PCV2 vaccines, their efficacy varies, influenced by co-infection and evaluation methods. This study assessed the efficacy of Ingelvac CircoFLEX® PCV2 vaccine under natural conditions. One hundred serum samples were collected from vaccinated and non-vaccinated piglets aged 21 to 173 days. PCR and antibody positivity rates did not show significant differences between the two groups, but PCV2 gene load at 91 days was significantly lower (p = 0.0095) in the vaccinated group. Anti-PCV2 antibody titers were also significantly lower in the vaccinated group at 91, 145, and 173 days (p < 0.0001). PCV2 was isolated from 50% of piglets in the non-vaccinated group (50%), compared with none (0%) in the vaccinated group, suggesting that PCV2 gene load in the non-vaccinated group did not correlate with viremia. Both groups were positive for antibodies to porcine reproductive and respiratory syndrome virus (PRRSV) at 63 days, prior to the surge in PCV2 gene load, suggesting PRRSV may enhance PCV2 replication. These findings highlight that while the vaccine reduced PCVAD damage, evaluation should incorporate methods such as virus isolation instead of relying solely on PCR.