Fostera PRRS: Duration of Immunity Study

Fostera PRRS helps defend growing pigs against respiratory disease associated with PRRSV throughout the entire production cycle, allowing pigs to maximise post-challenge weight gains, says Zoetis.
calendar icon 1 August 2013
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Porcine reproductive and respiratory syndrome virus (PRRSV) continues to pose a significant economic threat for swine producers. A recent study estimated that PRRS costs the US pork industry $664 million annually ($1.8 million per day) in production-related losses.2 When costs associated with veterinary, biosecurity, and other disease-related expenses are included, the cumulative impact of PRRSV totals more than $1 billion per year. Since more than half of weaningage PRRSV-negative pigs become infected with PRRSV before going to market,2 vaccination and other control measures are required to help growing pigs defend themselves against PRRSV.

When selecting a PRRSV vaccine, the duration of immunity (DOI) provided by a product is an important, fundamental consideration. The whole point of using a vaccine is to help provide pigs with an extended period of protective immunity that encompasses key times when natural disease resistance is low (e.g., stress events, nutritional changes) and/or when disease challenges are high. Therefore, the DOI of a vaccine can play a critical role in production management and helping prevent financial losses.

Unfortunately, little scientific information is available regarding the DOI offered by most PRRSV vaccines, primarily because DOI studies are generally not required to gain vaccine licensure. Vaccines are licensed, in part, with efficacy studies typically conducted within just a few weeks following vaccination. Though demonstrating short-term efficacy is important, DOI information is also important to help ensure animals are protected throughout the entire production cycle when respiratory disease exposure is often intense and immunity may be challenged.

Fostera™ PRRS

Fostera PRRS, from Zoetis, is the first and only PRRSV vaccine that helps prevent respiratory disease associated with PRRSV with a duration of immunity of at least 24 weeks. Fostera PRRS helps optimize performance by helping minimize the adverse affects of a subsequent PRRSV challenge, thereby allowing growing pigs to help maximize their postchallenge weight gain.3 Fostera PRRS is the outcome of breakthrough research by Zoetis scientists that discovered a key cellular receptor protein for the PRRS virus, thus prompting creation of unique cell lines for the growth and attenuation of PRRS viruses. Fostera PRRS offers a single-dose, easy-to-use formulation containing a modified-live PRRSV created from a US field strain that was attenuated through 52 passages on an innovative non-simian cell line, with no reversion to virulence.4

Fostera PRRS is approved for the vaccination of healthy, susceptible swine 3 weeks of age or older in PRRSV-positive herds or seronegative pigs deemed at risk for exposure to PRRSV as an aid in preventing respiratory disease associated with PRRSV. Fostera PRRS is administered as a single 2-mL intramuscular (IM) dose, after aseptic rehydration of the freeze-dried vaccine with sterile diluent provided.

Unlike other vaccines that ‘control’ disease, Fostera PRRS is the only vaccine to earn the ‘aid in prevention’ designation by the USDA. This distinctive license was based on previous PRRSVchallenge research that showed Fostera PRRS vaccination reduced lung lesions by 84 per cent, reduced overall respiratory clinical signs by 80 per cent, and improved average daily gain (ADG) by 2.5-times compared to challenged, non-vaccinated controls.3

In addition, further research has yielded yet another distinction for Fostera PRRS as it is the first and only PRRSV vaccine to demonstrate a 24-week duration of immunity after a single vaccination. As a result, the USDA has licensed the addition of this unique 24-week DOI to the Fostera PRRS label, an even more innovative attribute that further differentiates Fostera PRRS from other PRRSV vaccines. A summary of research supporting the 24-week DOI for Fostera PRRS follows.

Experiment Design

A study was conducted at a research facility to investigate the DOI provided by Fostera PRRS vaccination in swine challenged with a virulent, heterologous PRRSV.1 The 178-day study involved 48 healthy, weaned crossbred pigs approximately 3 weeks of age that had not been vaccinated for any diseases or treated with any medications, and were determined to be negative for PRRSV (ELISA) and PCV2 (PCR). Piglets were randomly assigned to 2 treatment groups and received vaccination on day 0 of the study as follows (Figure 1):

  • Fostera PRRS: 2 mL IM in neck (n=24);
  • Control: 2 mL of a placebo vaccine IM in the neck (n=24).

Figure 1. Study design and timeline.

During the 24-week ‘vaccination phase’ of the study, the 2 treatment groups were housed in separate rooms with each group occupying a single pen. Pigs were moved from nursery housing to a grower-finishing unit at the appropriate production phase. Animals were fed age-appropriate non-medicated rations throughout the study, with feed and water provided ad libitum.

On study day 168 (24 weeks after vaccination, 27 weeks of age), each pig was challenged via both the IM and intranasal (IN) routes with medium containing virulent, heterologous PRRSV (strain NADC20 given in a total volume of 4 mL, 1 mL/nostril, 2 mL IM). Pigs were re-housed during this 10-day ‘challenge phase’ of the study, with 12 pens of 2 pigs each per treatment.

Starting 1 day prior to challenge (day 167) through 10 days post-challenge (day 178), all pigs were observed daily and clinical observations (condition, depression, sneezing, coughing, and respiratory distress) were recorded by personnel masked to treatment group assignments. Pigs were also weighed on days 167 and 178. At 10 days post-challenge (day 178), pigs were euthanized, necropsied, and lung lesions scored for the percentage of consolidation for each lobe (left cranial, left middle, left caudal, right cranial, right middle, right caudal, and accessory). Blood samples were collected from all pigs every 4 weeks during the study and prior to necropsy for determination of PRRSV serology (ELISA). The study was conducted in accordance with the Zoetis Institutional Animal Care and Use Committee.

Collected data were statistically analyzed by appropriate methods using each pig as an experimental unit, with statistical significance recognized at P≤0.05.


Only mild, low-incidence clinical signs of respiratory disease were observed after challenge, with no differences between treatment groups (P>0.05). Thus, the challenge infection generated sub-clinical PRRS, a common condition of great interest to swine practitioners.

Reduced lung lesions

Figure 2. Percent lung lesions 10 days after challenge with PRRSV.

Figure 3. Average daily gain from 1 day before to 10 days after PRRSV challenge.

Figure 4. Mean serological responses of treatment groups after vaccination.

The primary parameter for quantifying PRRS protection and DOI was the percent of lung lesions in Fostera PRRS vaccinates relative to controls (Figure 2). Pigs vaccinated with Fostera PRRS and challenged 24 weeks later with PRRSV averaged only 1.0 per cent lung consolidation at necropsy 10 days post-challenge.

This outcome represented a significant 92 per cent reduction (P≤0.0001) compared to the 12.1 per cent mean rate of lung involvement for pigs in the control group. Vaccination with Fostera PRRS helped provide a high degree of protection against respiratory pathology caused by virulent PRRSV challenge 24 weeks later.

Heavier post-challenge body weights

Though pre-challenge body weights (day 167) were similar between treatment groups (P>0.05), non-vaccinated control pigs lost an average of 17.4 lb by day 178 (10-days after challenge). In contrast, Fostera PRRS vaccinates continued to gain weight (6.4lb) after PRRSV challenge, generating significantly (P≤0.0001) improved ADG compared to controls (Figure 3). The sub-clinical PRRSV challenge infection quickly eroded performance of unprotected pigs, but Fostera PRRS vaccination 24 weeks earlier helped reduce performance degradation often associated with PRRS outbreaks (or in this case, in the absence of overt clinical signs).


Serologic results summarized in Figure 4 show that control pigs remained sero-negative for antibodies to PRRSV through the day of challenge. In contrast, all pigs vaccinated with Fostera PRRS developed antibody titers to PRRSV. Seroconversion was detected in 18 of 24 vaccinated pigs (75 per cent) by 4 weeks after vaccination (the first post-vaccination sample), all seroconverted by day 56 (the next sample), and ELISA titers peaked at day 84 (12 weeks post-vaccination). Animals vaccinated with Fostera PRRS 24 weeks earlier clearly exhibited a substantive and rapid anamnestic response to the PRRSV challenge.

No adverse reactions related to vaccination were observed during the study.


Study results clearly demonstrate why Fostera PRRS is the first and only PRRSV vaccine to earn the label claim of "aids in prevention of respiratory disease associated with PRRSV with a duration of immunity of at least 24 weeks." After challenge with virulent, heterologous PRRSV, pigs vaccinated with Fostera PRRS 24 weeks earlier experienced:

  • Significant 92 per cent reduction in lung lesions (P ≤ 0.0001);
  • Significantly improved ADG (+0.6 lb, vs -1.6 lb for controls; P ≤ 0.0001). (Even though the incidence of clinical signs in control animals was low, the challenge infection exerted a large effect on ADG during the short post-challenge period.)

These outcomes confirm that Fostera PRRS helps defend growing pigs against respiratory disease associated with PRRSV throughout the entire production cycle, allowing pigs to maximize post-challenge weight gains. Pork producers can use Fostera PRRS in their herds with the confi dence that profit potential will not be threatened by PRRS outbreaks and associated performance losses that often conspire to dramatically increase production costs.


1. Data on file, Study Report No. 3121R-60-10-909, Zoetis Inc.
2. Holtkamp D, Kliebenstein J, Zimmerman J, Neumann E, Rotto H, Yoder T, Wang C, Yeske P, Mowrer C, Haley C. Assessment of the economic impact of porcine reproductive and respiratory syndrome virus on U.S. pork producer. National Pork Board Research Report 2011; NPB #10-158.
3. Data on file, Study Report No. 3127R-60-10-890, Zoetis Inc.
4. Data on file, Study Report No. 3425R-60-09-790, Zoetis Inc.

Further Reading

Find out more information on PRRS by clicking here.

August 2013

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