Vaccines contain antigens that make the body’s immune system produce antibodies that can protect against disease, which is known as an immune response. Antigens are modified or partial forms of the virus, bacteria, or toxin that cause the disease that the vaccine protects against. Because the antigen is altered from its original form, it cannot cause disease, but it can produce an immune response.
Vaccines can be injected using needles of different lengths and gauges. The needle gauge (G) refers to the width (diameter) of the needle. The higher the gauge number, the narrower the needle. For example, a 25 G needle is approximately 0.5 mm in diameter and is narrower than a 23 G needle, which has a diameter of 0.6 mm. Guidelines conflict regarding the lengths and gauges of needles that should be used for vaccinating children and adolescents.
We wanted to find out if the length and gauge of needles used to vaccinate children and adolescents has an influence on the:
1) immune response to the injected vaccine;
2) pain experienced during the vaccination procedure;
3) occurrence of reactions such as swelling, tenderness, and redness at the site where the vaccine is given; fever (high temperature); and other side effects that can occur after vaccination.
Quality of the evidence
We included five studies involving 1350 people. We rated the quality of the evidence from studies as very low, low, moderate, or high. Very low-quality evidence means that we are very uncertain about the results. High-quality evidence means that we are very confident in the results. There were problems with the design of some studies, and data were insufficient to answer some parts of our review question. The quality of the evidence from two studies was too low to allow us to draw any conclusions about the effects of the needles compared in the studies. However, there was sufficient evidence from the remaining three studies to allow us to reach conclusions.
The three studies that allowed us to reach conclusions involved 1135 healthy infants aged mostly between two and six months. The infants were vaccinated in the thigh with either 25 G 25 mm (narrow, long needles), 23 G 25 mm (wide, long needles), or 25 G 16 mm needles (narrow, short needles). The needles were inserted at right angles (90° angle) into the skin and pushed down into the muscle of the thigh. The vaccines injected were combination vaccines designed to protect against several diseases including diphtheria (D), tetanus (T), whooping cough (pertussis), and Haemophilus influenzae type b disease (Hib). The vaccines all contained whole-cell pertussis (wP) vaccine antigens. These vaccines are commonly used in low- and middle-income countries but not in high-income countries. Our review findings are therefore most relevant to low- and middle-income countries.
We found moderate-quality evidence that infants vaccinated in the thigh with 25 mm needles probably have fewer severe reactions (extensive redness and swelling in the thigh) after DTwP-Hib vaccination than infants vaccinated with 16 mm needles. We also found that the longer needles probably lead to fewer non-severe reactions such as mild swelling, tenderness, and redness after vaccination. The immune response to the vaccine is probably similar with the long and the short needles.
We found low-quality evidence that the wide, long needle may slightly reduce the pain of the vaccination procedure compared with the narrow, long needle. We found moderate-quality evidence that the wide, long needle probably slightly reduces the duration of crying immediately following vaccination compared with the narrow, long needle. The differences in pain and crying between use of the wide and narrow needles are probably too small to be of any practical importance.
We found low-quality evidence that infants vaccinated with the narrow, long needle may have slightly fewer non-severe reactions than infants vaccinated with the wide, long needle.
We do not know if needle size has an effect on fever or other reactions that sometimes occur after vaccination including drowsiness, loss of appetite, and vomiting due to the very low quality of the evidence.
The evidence in our review is current to October 2017.