By Barbara Greenwood Dufour

For many of us, getting a vaccine or other routine injection is not a pleasant experience. But there’s something comforting about the injection site being wiped with an alcohol swab. Other than signaling to us that it’s time to brace ourselves for the needle, it reassures us that good care is being taken to reduce the risk of infection. We know that without it we’d be inviting bacteria into the puncture wound. Or do we?

Alcohol swabbing before an injection is a long-standing, widely used infection control practice. It’s thought that prepping the skin using alcohol swabs removes bacteria that could be pushed into the puncture and might cause an infection. To clean the skin before a vaccination or other injection, suggested standard practice according to the World Health Organisation (WHO) is to swab the injection site with a saturated 60% to 70% alcohol swab for 30 seconds, then let the area dry for another 30 seconds so that the alcohol doesn’t enter the puncture and sting.

But, for many years there has been debate around whether this practice is effective for reducing infection. Not many patients arrive for their shot with dirty skin. And various health organizations — including the WHO and the Public Health Agency of Canada — say that if the skin is visibly clean, there’s no need to swab it with alcohol. Still, alcohol swabbing remains a common and routine practice in hospitals and other health care facilities across Canada and around the world, and those in the health care community continue to wonder if there’s any evidence that it’s preventing infection.

Decision-makers within the Canadian health care system recently turned to CADTH to find out. CADTH is an independent, evidence-based agency that finds, assesses, and summarizes the research on drugs, medical devices, and procedures. In response, CADTH searched for and critically appraised the available evidence on the clinical effectiveness of skin preparation prior to injections and produced a report on what was found.

When CADTH searched for published studies on this topic, it found that only one, the results of which were published in 2019, met the inclusion criteria for the review. The study was conducted in a Canadian outpatient clinic where children were receiving standard childhood vaccinations. Although all the children in this study had their arms swabbed with alcohol, half of them then received their injection in an area of skin that hadn’t been swabbed. Afterward, their parents were asked to report on whether their child experienced any skin reactions, pain, redness, swelling, or feelings of heat at the injection site.

The researchers who conducted this study reported that swabbing the injection site didn’t make any difference in patient outcomes in terms of local skin reactions, pain afterward, redness, swelling, or heat sensations. When the data related to pain was analyzed further, it turned out that the children who had received their injection into swabbed skin felt the pain from the needle for a longer time than those who received injections into unswabbed skin.

But, wait — what did the study say about the effect of alcohol swabbing on the incidence of skin infection? Unfortunately, the study wasn’t able to answer this specific question. Pediatricians who later examined the children found that none of them had developed a skin infection, whether or not they were swabbed; and, even if there had been any cases of infection, the researchers hadn’t been able to recruit enough children for the study to come to a meaningful conclusion on whether swabbing prevents infection.

Although the swabs themselves are inexpensive, the cost of using them is not insignificant when you consider how many of them are used during public vaccination programs. So, if the practice isn’t effective, it could be a waste of money. But, given that we’re not sure, maybe it represents a bit of precaution that’s worth the peace of mind. Until further research can inject some certainty about its effectiveness, some will continue to wonder if we should still be swabbing prior to routine injections and vaccinations. Most are probably just thinking about the needle.

To view CADTH’s full report, go to cadth.ca/skin-preparation-injections-review-clinical-effectiveness-cost-effectiveness-and-guidelines-0. If you would like to learn more about CADTH, visit cadth.ca, follow us on Twitter @CADTH_ACMTS, or speak to our Liaison Officer in your region: cadth.ca/liaison-officers.

Barbara Greenwood Dufour is a Knowledge Mobilization Officer at CADTH.