DNA Explainer: Needle-free COVID-19 vaccine injections - Here’s how that works

Gujarat-based pharmaceutical company Zydus Cadila is nearing emergency use approval for its pioneering needle-free COVID-19 vaccine from Drug Controller General of India (DCGI). To achieve needle-free drug delivery, the ZyCoV-D vaccine will use the ‘Jet Injector’ method of administration, a technique where the needle piercing the skin is replaced by pressure injecting the liquid directly through the upper layer of the skin and into the underlying tissues.

This technique is not new and has been around for more than a century. The first jet injector for needle-free vaccine administration was showcased in 1866. 

How jet injection works?

A method developed around the same time as needle injections, jet injectors deliver drugs to a person via a narrow, high-pressure stream of liquid which penetrates the outermost skin layer. This intradermal delivery does not make the arm sore like needle-based injections, also reducing the side effects from the jab.

The same technology also finds application as fuel injectors in automobile engines. In this needle-free approach, a highly-pressurized jet stream powered by of a spring or compressed gas administers the dosage directly to the skin without piercing it. The method was used extensively in the 1960s for mass small pox vaccination drives. Jet injectors were also a common method of delivering different vaccines quickly to large groups of people, like in armies.

Their usage, however, declined due to risk of disease transmission. Blood shooting out from the pressure puncture spot could contaminate the tip of the fuel injector, which led to at least one documented outbreak of Hepatitis B at a weight-loss clinic in the US in the 1980s. However, with new technological advances, there’s been significant progress to minimize any chances of cross contamination.  

With new jet injector devices much safer, the International Standards Organization (ISO) has made a call to refer to them as "needle-free injectors" rather than the term "jet injector”, a term that is often attached to the risk of cross-contamination.

The ZydusCadila needle-free COVID-19 vaccine

The ZyCov-D vaccine uses a needle-free method called Tropis, developed by American company Pharmajet. The method uses a “single-use, sterile, disposable syringe used with a reusable injector” which reduces the risk of cross contamination as well as eradicates the issue of needle injury.

Furthermore, the ZyCoV-D uses a different vaccine development technology compared to earlier vaccines which use mRNA (messenger ribonucleic acid), adenoviral vectors and inactivated virus among other methods. ZyCoV-D is the first DNA plasmid based COVID-19 vaccine.

As per Dr. Sharvil Patel, Managing Director, Cadila Healthcare Ltd., “This breakthrough marks a key milestone in scientific innovation and advancement in technology. As the first ever plasmid DNA vaccine for human use, ZyCoV-D has proven its safety and efficacy profile in our fight against COVID-19. The vaccine when approved will help not only adults but also adolescents in the 12 to 18 years age group.”