Is there an important difference between the mRNA shots for COVID and the shots developed with the viral vector technology (such as the Johnson & Johnson one)?
Yes, there are important differences between the mRNA COVID-19 vaccines (such as the Pfizer-BioNTech and Moderna vaccines) and the viral vector vaccine (such as the Johnson & Johnson vaccine).

The mRNA vaccines work by using a small piece of genetic material called messenger RNA (mRNA) to instruct cells in the body to produce a harmless piece of the spike protein found on the surface of the SARS-CoV-2 virus. This triggers an immune response that can help protect against COVID-19. The mRNA vaccines do not contain live virus or inactivated virus particles, and they do not change a person's DNA.

The viral vector vaccine works by using a harmless virus (in the case of the Johnson & Johnson vaccine, a modified adenovirus) to deliver a piece of the spike protein gene into cells. The cells then produce the spike protein, which triggers an immune response. The viral vector vaccine also does not contain live virus, but it does use a virus to deliver genetic material into cells.

One important difference between the mRNA and viral vector vaccines is the number of doses required. The Pfizer-BioNTech and Moderna vaccines both require two doses, while the Johnson & Johnson vaccine only requires one dose.

Another difference is the storage and handling requirements. The mRNA vaccines need to be stored at very cold temperatures, while the Johnson & Johnson vaccine can be stored at regular refrigerator temperatures.

Finally, there have been some differences in the reported efficacy rates for the vaccines. For example, the clinical trials for the Johnson & Johnson vaccine showed slightly lower efficacy against overall COVID-19 infection compared to the mRNA vaccines. However, all of the vaccines have been shown to be highly effective at preventing severe disease, hospitalization, and death from COVID-19.

It's important to note that all of the authorized COVID-19 vaccines have undergone rigorous testing and have been shown to be safe and effective at preventing COVID-19. People should get whichever vaccine is available to them and recommended by their healthcare provider.