Point-of-Care Ultrasound Is a Valuable Modality During Mass COVID-19 Vaccination Campaigns.

Coronavirus disease 2019 has become a widespread public health crisis across the globe, requiring multiple approaches to containment, treatment, and prevention. Vaccines are an important tool to prevent morbidity and mortality from this devastating virus. Ensuring direct administration of vaccines into target tissue helps provide an optimal immune response while decreasing unintended adverse effects. Point-of-care ultrasound can better assist clinicians to determine appropriate needle length and penetration level especially in special populations. Examples include patients who are obese, pregnant, or with refractory lymphedema, and those living in areas where needle supply is unstable or insufficient.

Coronavirus disease 2019 (COVID‐19) is a novel infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). Since its beginning in late 2019, the widespread pandemic has become a major threat to healthcare systems worldwide. In addition to nonpharmacologic intervention, adequate and prompt vaccination coverage is important to create herd immunity and prevent SARS‐CoV‐2 transmission. The pharmaceutical industry has been working hard to develop effective and safe vaccines against COVID‐19 since the outbreak of this global pandemic. As of July 1, 2021, a total of 105 clinical candidate vaccines for the prevention of COVID‐19 currently exist according to the World Health Organization landscape summary, of which seven have been approved for use. Vaccines are being used worldwide, and their mechanisms of action and efficacies vary.

It is recommended that all COVID‐19 vaccines be injected intramuscularly. Clinically, the deltoid muscle is the preferred site for anatomical landmark‐guided intramuscular injection; however, vaccines must be administered directly to the target tissue to achieve an optimal immune response. Incorrect needle placement may lead to an inadequate immune response due to poor blood supply to the subcutaneous tissue, resulting in slow mobilization and processing of antigens, which causes vaccine failure and detrimental side effects, such as unintended cutaneous reactions, granuloma formation, infection, shoulder dysfunction, bone contusion, and partial posterior cord brachial plexus injury. , ,

To ensure accurate needle placement, the needle must pass through the subcutaneous layer and adequately penetrate the deltoid muscle. Based on extant research in which the deltoid fat pad thickness was measured using musculoskeletal ultrasound, a standard 16‐mm (5/8‐in.) needle will not reach 5 mm into the deltoid muscle, the common needle length for deltoid intramuscular injection, in 17% of men and 48.4% of women. Cook, Poland et al, and Zuckerman advocated for individualization of needle length, and a previous study has shown that using a 25‐mm needle can lead to potential underpenetration in men with a body weight of >118 kg and women with a body weight of >90 kg. , , Therefore, a one‐size‐fits‐all needle length will not always guarantee successful intramuscular injection.

Point‐of‐care ultrasound (POCUS) is a widely available, noninvasive, portable, and easy‐to‐learn tool that is already used in various clinical settings, and we believe that it may play a valuable role in the individualization of needle length and in determining the ideal depth of intramuscular injection for special populations such as those with comorbidities that affect the thickness of the subcutaneous tissue. Therefore, POCUS may be useful during intramuscular injection for vaccination under the following conditions: 1) when the deltoid fat pad is likely to be thicker than the default needle length, such as in individuals with high body mass index, breast cancer patients with uncontrolled lymphedema, pediatric patients, and pregnant women; 2) when there is insufficient or unstable supply of needles of a certain length due to the global public health crisis, which may result in the depletion of medical supplies.

Knowledge regarding the appropriate skin‐to‐muscle distance for individuals of different ethnicities and ages is still lacking. Further studies should analyze the correlation of subdeltoid fat pad thickness with age, ethnicity, and body shape and evaluate sex differences in subdeltoid fat pad thickness. Although the duration of vaccine‐elicited protection remains unclear, periodic booster injections may be required to maintain active protection against SARS‐CoV‐2 and its variants. POCUS may be a valuable tool for improving the efficacy of vaccine administration and reducing the risk of unintended complications, especially among special populations.

In this regard, we demonstrate that two females with similar body mass index (BMI) could have a very different skin‐to‐muscle distance as detected by ultrasonography (Figures 1 and 2). Informed consent was obtained from all individuals who participated in the ultrasonographic demonstration. The difference in skin‐to‐muscle distance could cause potential under penetration if needle length selection was solely based on weight, based on US Centers for Disease Control and Prevention guidelines (Figure 2).

Figure 1

A, Case 1 was a 42‐year‐old female. Height 163 cm, weight 73 kg, BMI 26.1. Linear probe was placed at the standard site for intramuscular injection. B, Skin‐to‐muscle distance was measured as 10 mm. Based on CDC recommendation, 25‐mm needle should penetrate deltoid muscle adequately. BMI, body mass index. CDC, Centers for Disease Control and Prevention.

Figure 2

A, Case 2 was a 24‐year‐old female. Height 156 cm, weight 65 kg, BMI 26.7. Linear probe was placed at the usual site for intramuscular injection. B, Skin‐to‐muscle distance was measured as 20.7 mm. If 25‐mm needle was used based on CDC recommendation, potentially inadequate penetration of deltoid muscle could occur if the deltoid muscle is bunched or needle is not fully advanced into the target site. BMI, body mass index. CD, Centers for Disease Control and Prevention.