General Principle of Vaccination:  

Different types of vaccines should not be administered simultaneously, nor should vaccines be used concurrently with chemical pharmaceuticals.  

However, in recent years, the increasing complexity of livestock and poultry diseases—particularly swine diseases—has led to the use of more vaccine types, making immunization scheduling more challenging. Multiple vaccines often need to be administered within the same timeframe, sometimes alongside preventive, therapeutic, or disinfectant drugs. As a result, the conventional principles of vaccination no longer fully meet the evolving needs of field practice. The following approaches are recommended to address these two issues:  

I. Simultaneous Administration of Different Types of Vaccines  

When immunization scheduling is constrained and different vaccines must be administered at the same time:  

- Generally, two inactivated vaccines, or one inactivated vaccine and one live attenuated vaccine, may be administered simultaneously at different injection sites.  

- However, administering two or more live attenuated vaccines simultaneously may cause interference and reduce efficacy.  

- Exceptions exist: some manufacturers’ highly pathogenic porcine reproductive and respiratory syndrome (PRRS) vaccines may be co-administered with classical swine fever live vaccines, as specified in the product instructions.  

- Polyvalent or combination vaccines are designed with consideration of interactions between strains and may be used with confidence.  

- A one-week interval is recommended between two immunization events.  

II. Concurrent Use of Vaccines and Chemical Pharmaceuticals  

1. Live Vaccines and Chemical Pharmaceuticals  

   Since live vaccines rely on the replication of viable antigens in the host to induce immunity, the compatibility with pharmaceuticals depends on the drug type:  

   - For bacterial live vaccines: avoid antibacterial drugs (e.g., broad-spectrum antibiotics) for 3 days before and 5–7 days after vaccination.  

   - For viral live vaccines: most antibacterial drugs have minimal impact, provided the vaccine and drug do not come into direct contact. Preventive or therapeutic antibiotics may be used judiciously, but antiviral drugs are strictly prohibited.  

   - Additionally, antibiotics such as furazolidone, chloramphenicol, kanamycin, and sulfonamides may suppress B-lymphocyte proliferation and impair immune responses. Avoid these drugs—or feed additives containing them—for 10 days before and after vaccination.  

2. Inactivated Vaccines and Chemical Pharmaceuticals  

   With the exception of the immunosuppressive antibiotics mentioned above, chemical pharmaceuticals may generally be used alongside inactivated vaccines.  

3. Disinfection During Immunization  

   - For live vaccines administered via drinking water, nasal drops, or spray, disinfection should be suspended for 2–3 days before and after immunization. Under special circumstances, disinfection may resume 2 hours post-vaccination.  

   - In other scenarios, disinfection may be paused for 2–3 days if feasible.  

   - During emergency vaccination in outbreak situations, timely disinfection remains essential. It helps block pathogen invasion while immunity is developing, buying critical time for the host to mount a protective response.