Covid-19 Vaccines: Boosting Effectiveness through Epicutaneous Immunization
A key factor for the approval and wide adoption of a covid-19 vaccine is its effectiveness.
Ideally, any covid-19 vaccine considered should be above the 90% effectiveness mark, but some are in the 50–70% range or even lower, despite being determined as safe for use in Humans in all clinical trials phases.
For instance, the promising AstraZeneca vaccine has a reported 70% efficacy and the Sinovac vaccine is just above the 50% mark in a clinical trial in Brasil. And those are only some of the 18 vaccines currently in efficacy testing. 
Wouldn’t it be beneficial to increase the efficacy using a simple know and tested procedure?
Recently, Harvard Researchers have studied the immune response induced by a vaccine against respiratory virus administered through epicutaneous immunization — also known as skin scarification. 
Vaccine through epicutaneous immunization was widely and successfully used against smallpox — a respiratory virus — in the past. It was easier to administrate and didn’t require the material and equipment necessary for the hypodermic syringe method. 
It seems that the epicutaneous immunization might be more effective against respiratory virus, like the new coronavirus, since this procedure produced more lung-specific T cells than the other methods. 
This study was performed on mice.  However, considering this method was used in Humans in the past against smallpox, I pose that it might be scientifically and medically fruitful to test the inoculation of low-efficacy covid-19 vaccines in Humans using skin scarification and determine if there is any increase in effectiveness while maintaining the required safety.
Also, the World now struggles to achieve herd immunity by vaccination.  Since some available vaccines — like Pfizer-BioNTech and Oxford/AstraZeneca — require double dosage to achieve an acceptable efficacy , I also pose that one should scientifically test the hypothesis of increasing the efficacy of the first dose through epicutaneous immunization. If this hypothesis is confirmed, this could perhaps preclude the need for a second dose and, consequently, allow a more rapid immunization of the World’s population with clear benefits in terms of public health.