Efforts worldwide to immunize children against a host of preventable diseases depend on adherence to recommended immunization schedules. If adhered to, most vaccines will be administered to children by the age of 6 years, and children can receive multiple injections in a single office visit. By the age of 2 years, for example, children in the United States can receive up to 24 injections and up to 5 in a single office visit.1
Among concerns with administering these multiple and frequent immunizations in young children are the potential pain and adverse effects associated with injections. Along with inducing pain in some children, the early negative experience of needle-related procedures can interfere with adherence to immunization schedules and create long-lasting effects of anxiety and stress around needle-related procedures that remain into adulthood.1
There are some conflicting guidelines regarding the lengths and gauges of needles that should be used for vaccination procedures in children and adolescents. Given the need for strong adherence to immunization schedules as well as the desire to reduce any adverse effects associated with injections, investigators at University College Cork, Ireland, undertook a Cochrane Systematic Review of the literature for evidence on whether different lengths and gauges of needles used for administering vaccines to children have an effect on the immune response to the vaccine, procedural pain, reactogenicity events, and adverse effects after the procedure.2
Published in 2015, the Cochrane Systematic Review included 5 randomized controlled trials involving 1350 participants. Two of these trials were small and the evidence was insufficient to be confident about the effects of needle size and needle gauge on vaccine immunogenicity or reactogenicity. The remaining 3 trials (1135 participants), in infants predominately aged 2 to 6 months, allowed comparisons to be made between 25-G, 25-mm; 23-G, 25-mm; and 25-G, 16-mm needles. Moderate quality evidence from 1 trial showed that there was probably little or no difference in immune response, which was the first research objective of the study. However, some data did suggest that longer needle size (25 mm versus 16 mm) may have some, albeit a moderate, effect on reducing pain and adverse effects of injections.2
“Based on the evidence, it would seem that using a 25-mm needle as opposed to a 16-mm needle would be recommended to reduce the occurrence of local reactions,” says study investigator Frances Shiely, PhD, HRB Clinical Research Facility and Department of Epidemiology and Public Health, University College Cork. “Though the data from the study will only support making this claim in infants aged 2 to 6 months, it would be reasonable to use the same conclusions when choosing needle length to vaccinate older children and adolescents.”
The Cochrane Systematic Review included review of 5 randomized controlled trials that assessed the effects of needle length (16 mm and 25 mm) and gauge (25 G and 23 G) on the administration of vaccines to children aged up to 24 years.
After reviewing each study for the quality of the evidence, the investigators eliminated 2 of the studies based on their very low quality that disallowed the ability to draw any conclusions. (The quality of evidence in a Cochrane Systematic Review may be rated as “high” [very confident about the findings] to “very low” [very uncertain about the findings], with “moderate” and “low” quality in between.)
The 3 studies included in the analysis involved 1135 healthy infants, most aged between 2 and 6 months. All infants underwent intramuscular vaccination in the anterolateral thigh via the technique recommended by the World Health Organization: stretching the skin on the thigh flat and inserting a needle at a 90-degree angle and up to the hub. Needles used in the studies included 25-G, 25-mm; 23-G, 25-mm; and 25-G, 16-mm needles. Vaccines delivered contained combination vaccines (DTwP with a reactogenic whole-cell pertussis antigen component) designed to protect against multiple diseases, including diphtheria, tetanus, pertussis, and Haemophilus influenzae type b.
Looking at the evidence
None of the evidence from the 3 trials was considered high quality, and several of the findings were considered low or very low quality. The only evidence that provides some guidance on the choice of needle size is data showing moderate quality evidence that suggests a reduction in local reactions when using longer (25-mm) needles. Using the NNT (numbers need to treat) calculation, the investigators estimated that for every 25 infants vaccinated, 1 fewer infant will experience a nonsevere local reaction after the first vaccine dose if the vaccine is administered with a long needle versus a short needle. For every 5 to 8 infants vaccinated, 1 fewer infant will experience a nonsevere local reaction at 24 hours after the first, second, and third vaccine doses if the vaccine is administered with a long versus short needle.2
Although moderate quality evidence was also found for a slight reduction in crying time immediately following the procedure when using the wider gauge needle compared with the narrow gauge needle, the slight difference found was too small to be of any practical importance.
“The comparative effects of 23-G, 25-mm; 25-G, 25-mm; and 25-G, 16-mm needles on the incidence of postvaccination 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,” says Shiely.
The Table lists the findings and quality of evidence.
Results most relevant to developing countries
Emphasized in the study was the use of DTwP vaccines with a reactogenic whole-cell pertussis antigen component. The investigators highlight that combination vaccines containing pertussis antigens are most commonly used in developing countries. As such, the findings are most relevant to developing countries.2
Overall, Shiely underscores that “the findings are applicable to healthy infants aged 2 to 6 months receiving combination DTwP vaccines with a reactogenic whole-cell pertussis antigen component.”2
Take home message
One main message of the study, according to Shiely, is that the quality of evidence was not sufficient to draw any firm conclusions. As such, she emphasizes the need for higher quality research. “If you are involved in research in your area, seek assistance from a statistician or an epidemiologist who can help you design a better study that will allow pediatricians around the world to draw meaningful conclusions,” she says.
The second message is, she says, “when given a choice, the longer needle (25-mm rather than 16-mm) is probably best for vaccinations.”
1. Beirne PV, Shiely F, Hennessy S, Fitzgerald T, MacLeod F. Needle size for vaccination procedures in children and adolescents (protocol). Cochrane Collaboration. John Wiley and Sons Ltd; 2013. Available at: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD010720/pdf. Accessed April 13, 2017.
2. Beirne PV, Hennessy S, Cadogan SL, Shiely F, Fitzgerald T, MacLeod F. Needle size for vaccination procedures in children and adolescents. Cochrane Database Syst Rev. 2015;(6):CD010720.