Vaccines contain antigens that make our immune system produce antibodies that can protect against disease. Antigens are modified or partial forms of the virus, bacteria, or the 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 millimetres (mm) in diameter and is narrower than a 23 G needle, which has a diameter of 0.6 mm. There are some conflicting guidelines regarding the lengths and gauges of needles that should be used for vaccinating children and adolescents.
We wanted to discover if the length and gauge of needles used to vaccinate children and adolescents has an influence on:
1) the immune response to the injected vaccine;
2) the pain experienced during the vaccination procedure;
3) the 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 using four levels: 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 there were not enough data 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 that were compared in the studies. There was sufficient evidence from the remaining three studies to allow us to reach some conclusions.
The three studies 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 developing but not in developed countries. Our review findings are therefore most relevant to developing countries.
We found moderate quality evidence that infants vaccinated in the thigh with 25 mm needles probably get 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 long and the short needles probably produce a similar immune response to the vaccine.
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 results in a slight reduction in the duration of crying immediately following vaccination compared with the narrow long needle. The differences in pain and crying between 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 get 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. This is because the quality of the evidence is too low.
The evidence in our review is current to November 2014.
Using 25 mm needles (either 23 G or 25 G) for intramuscular vaccination procedures in the anterolateral thigh of infants using the WHO injection technique probably reduces the occurrence of local reactions while achieving a comparable immune response to 25 G 16 mm needles. These findings are applicable to healthy infants aged two to six months receiving combination DTwP vaccines with a reactogenic whole-cell pertussis antigen component. These vaccines are predominantly used in developing countries. The applicability of the findings to vaccines with acellular pertussis components and other vaccines with different reactogenicity profiles is uncertain.
Hypodermic needles of different sizes (gauges and lengths) can be used for vaccination procedures. The gauge (G) refers to the outside diameter of the needle tubing. The higher the gauge number, the smaller diameter of the needle (eg a 25 G needle is 0.5 mm in diameter and is narrower than a 23 G needle (0.6 mm)). Many vaccines are recommended for injection into muscle (intramuscularly), although some are delivered subcutaneously (under the skin) and intradermally (into skin). Choosing an appropriate length and gauge of a needle may be important to ensure that a vaccine is delivered to the appropriate site and produces the maximum immune response while causing the least possible harm. There are some conflicting guidelines regarding the lengths and gauges of needles that should be used for vaccination procedures in children and adolescents.
To assess the effects of using needles of different lengths and gauges for administering vaccines to children and adolescents on vaccine immunogenicity (the ability of the vaccine to elicit an immune response), procedural pain, and other reactogenicity events (adverse events following vaccine administration).
We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2014, Issue 10), MEDLINE and MEDLINE in Progress via Ovid (1947 to November 2014), EMBASE via Ovid (1974 to November 2014), and CINAHL via EBSCOhost (1982 to November 2014). We also searched reference lists of articles and textbooks, the proceedings of vaccine conferences, and three clinical trial registers.
Randomised controlled trials evaluating the effects of using hypodermic needles of any gauge or length to administer any type of vaccine to people aged from birth to 24 years.
Three review authors independently extracted trial data and assessed the risk of bias. We contacted trial authors for additional information. We rated the quality of evidence using the GRADE system.
We included five trials involving 1350 participants. Data for the primary review outcomes were either absent (for the incidence of vaccine-preventable diseases) or limited (for procedural pain and crying). The available evidence was compromised by the use of surrogate immunogenicity outcomes, incomplete blinding of outcome assessors, and imprecision for some outcomes. The evidence from two small trials was insufficient to allow any confident statements to be made about the effects of the needles evaluated in the trials on vaccine immunogenicity and reactogenicity.
The remaining three trials (1135 participants) contributed data to comparisons between 25 G 25 mm, 23 G 25 mm, and 25 G 16 mm needles. These trials involved infants predominantly aged two to six months undergoing intramuscular vaccination in the anterolateral thigh using the World Health Organization (WHO) injection technique (skin stretched flat, needle inserted at a 90° angle and up to the needle hub in healthy infants). The vaccines administered were combination vaccines containing diphtheria, tetanus, and whole-cell pertussis antigens (DTwP). In some trials, the vaccines also contained Haemophilus influenzae type b (DTwP-Hib) and hepatitis B (DTwP-Hib-HepB) antigen components.
We found moderate quality evidence from one trial that there is probably little or no difference in immune response, defined in terms of the proportion of seroprotected infants, between using 25 G 25 mm, 23 G 25 mm, or 25 G 16 mm needles to administer a series of three doses of a DTwP-Hib vaccine at ages two, three, and four months (numbers of participants in analyses range from 309 to 402. Immune response to pertussis antigen not measured).
25 mm needles (either 23 G or 25 G) probably lead to fewer severe local reactions (extensive redness and swelling) and fewer non-severe local reactions (any redness, swelling, tenderness or hardness (composite outcome)) after DTwP-Hib vaccination compared with 25 G 16 mm needles. We estimate that one fewer infant will experience a severe local reaction after the first vaccine dose for every 25 infants vaccinated with the longer rather than the shorter needle (number needed to treat (NNT) 25 (95% confidence interval (CI) 15 to 100)). We estimate that one fewer infant will experience a non-severe local reaction at 24 hours after the first, second, and third vaccine doses for every five to eight infants vaccinated with the longer rather than the shorter needle (NNTs range from 5 (95% CI 4 to 10) to 8 (95% CI 5 to 34)) (moderate quality evidence, one trial for first and second doses, two trials for third dose, numbers of participants in analyses range from 413 to 528).
Using a wider gauge needle (23 G 25 mm) may slightly reduce procedural pain (low quality evidence) and probably leads to a slight reduction in the duration of crying time immediately after vaccination (moderate quality evidence) compared with a narrower gauge (25 G 25 mm) needle (one trial, 320 participants). The effects are probably not large enough to be of any clinical relevance. The 25 G 25 mm needle may produce a small reduction in the incidence of local reactions after each dose of a DTwP vaccine compared with the 23 G 25 mm needle, but the effect estimates are imprecise (low quality evidence, two trials, numbers of participants in analyses range from 100 to 459).
The comparative effects of 23 G 25 mm, 25 G 25 mm, and 25 G 16 mm needles on the incidence of post-vaccination fever, persistent inconsolable crying, and other systemic events such as drowsiness, loss of appetite, and vomiting are uncertain due to the very low quality of the evidence.