Needle replacement before subcutaneous vaccination in dogs: a randomized clinical trial finds no clinical benefit

To determine whether replacing needles after vial septum puncture affects canine response to vaccination and whether injectors can distinguish between replaced and nonreplaced needles.

In this randomized, double-blinded, controlled crossover trial conducted at the Midwestern University College of Veterinary Medicine vaccine clinics between June and August of 2024, 75 client-owned dogs received both rabies and distemper, hepatitis, parainfluenza, and parvovirus vaccines, one with a replaced needle and one with the original needle used to draw up the vaccine. Heart rate (HR) was recorded continuously, reaction to needle insertion was scored on a 5-point scale by 2 blinded observers, and injectors guessed which syringe had the replaced needle. The outcomes of HR change between baseline and maximum after insertion and mean reaction rating were analyzed with linear mixed-effects models and injector guess with a 1-sample test of proportions.

45 dogs (60%) provided complete HR data. Change in HR for replaced as compared to nonreplaced needles was not different (β = -0.8; 95% CI, -12 to 10). Heart rate was higher for rabies administered second (β = 23; 95% CI, 7 to 40). Reaction scores did not differ (β = -0.05; 95% CI, -0.24 to 0.14). Injectors identified replaced needles 46% of the time (95% CI, 34 to 58), which was not better than chance.

Needle replacement did not improve patient comfort, and injectors were unable to perceive a difference between replaced and nonreplaced needles.

Injecting dogs with the same needle used for drawing up vaccines is clinically acceptable. Replacement provides no measurable patient benefit while adding risk, waste, and cost.