Study Finds No Clinical Benefit to Replacing Needles Before Subcutaneous Vaccination in Dogs

A new randomized clinical trial published in the Journal of the American Veterinary Medical Association examined whether replacing a needle after puncturing a vaccine vial improves comfort for dogs receiving subcutaneous vaccinations. The findings suggest it does not.

The study, conducted at Midwestern University College of Veterinary Medicine vaccine clinics between June and August 2024, evaluated physiological and behavioral responses in dogs receiving routine rabies and DHPP vaccinations. Researchers also assessed whether veterinary professionals administering the injections could perceive a difference between replaced and nonreplaced needles.

Study Design and Methods

The trial enrolled 75 client-owned dogs that met health and handling criteria, including low fear, anxiety, and stress (FAS) scores. Each dog received two vaccines—one administered with a needle that had been replaced after drawing up the vaccine and one with the original needle—using a randomized, double-blinded, crossover design.

Heart rate was continuously monitored as an objective measure of autonomic response, and behavioral reactions to needle insertion were scored by two blinded observers using a standardized five-point scale. Injectors, who included veterinarians, technicians, and students, were asked to guess which injection used a replaced needle based solely on feel.

Key Findings

Among the 45 dogs with usable heart rate data, no significant difference was found in heart rate changes between injections given with replaced versus nonreplaced needles. Behavioral reaction scores were also similar between the two conditions across all 75 dogs.

Injectors were unable to reliably distinguish between replaced and nonreplaced needles. When accounting for incorrect and “don’t know” responses, correct identification occurred at a rate consistent with chance.

The study did identify other factors associated with increased heart rate or reactivity, including vaccine order and injection location. Rabies vaccines administered in the rear limb as the second injection were associated with higher heart rate responses, suggesting that order and site may influence stress more than needle replacement.

Context Within Veterinary Practice

Needle replacement after vial puncture is a common practice in veterinary medicine, often based on concerns about needle dulling and patient comfort. Previous in vitro studies have shown minimal changes in needle penetration force after a single vial puncture, but the clinical relevance of those findings has remained unclear.

This study adds in vivo evidence indicating that such changes do not translate into measurable differences in canine comfort during routine subcutaneous vaccination. The authors note that routine needle replacement also introduces considerations related to occupational safety, medical waste, and cost, though these were not primary outcomes of the trial.

Interpretation and Limitations

The authors emphasize that the findings apply to single vial punctures using one needle type and gauge and to dogs with relatively low baseline stress levels. The study did not assess repeated vial punctures, other needle brands or sizes, or highly fearful patients.

While reaction scoring was subjective, inter-rater agreement was strong, and results aligned with objective heart rate data. Each dog served as its own control, strengthening internal validity.

Takeaway

In this controlled clinical setting, replacing a needle after drawing up a vaccine did not improve measurable indicators of comfort in dogs, nor could injectors reliably perceive a difference. The findings suggest that, for routine subcutaneous vaccination following a single vial puncture, needle replacement does not provide a demonstrable clinical advantage.

As with many long-standing clinical habits, the authors note that decisions around needle handling may benefit from continued evaluation as evidence evolves.

Read the full study here: https://avmajournals.avma.org/view/journals/javma/aop/javma.25.10.0661/javma.25.10.0661.xml