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Although live mixed coccidiosis vaccines are widely used for Eimeria control, the side effects (e.g., damaging the intestinal mucosa and decreasing their weight gain) are not negligible. This study aimed to filter out the lowest dose of coccidiosis mixed vaccine with Lactococcus lactis (L. lactis) NZ3900/pNZ8149‐IL‐4‐IL‐2 (RLIL4/2) coimmunization against Eimeria reduces the side effects for Eimeria vaccination. Chickens oral 1.0 ×, 0.9 ×, 0.8 ×, 0.6 ×, 0.4 × dose of live vaccine, and RLIL4/2 with 1.0 × 109 CFU/chicken, respectively. The blank control group, challenge‐only group and 1.0 × dose vaccine‐only group are used as references. The survival rate, weight gain, bloody stool, intestinal lesions scores, oocyst output oocysts per gramme (OPG), and anticoccidial index (ACI) were detected by challenging with virulent coccidiosis. All the results indicated that the weight gain during the immune period or bloody stool/intestinal lesions scores/OPG during the challenge period were oppositely correlated with vaccine doses. The survival rate, weight gain, and ACI were positively correlated with vaccine doses during the challenge period. The ACI of 0.6 × the dose group was 167.69, which was considered a moderate efficiency. The weight gain, ACI of 1.0 ×, 0.9 × and 0.8 × dose groups were higher or intestinal lesions were lower than 1.0 × dose vaccine‐only group (p < 0.05), respectively. In conclusion, the coimmunization of RLIL4/2 with Eimeria mixed vaccine could reduce 40% of the dose and the side effects (e.g., weight gain and intestinal lesions) from live mixed coccidiosis vaccine.