Johnson & Johnson's newly authorized COVID-19 vaccine has started shipping and its top executive said on Monday that Americans should be able to receive the single-dose shot within the next 24 to 48 hours, adding a third vaccine in the United States.

The drugmaker plans to deliver 4 million vaccine doses this week, 20 million by the end of March and 100 million doses by June, J&J Chief Executive Office Alex Gorsky said in interviews with NBC News' Today program and CNBC.

"Within the next 24 to 28 hours, Americans should start receiving shots in arms. They're literally rolling out with the trucks as we speak," he said to NBC News.

J&J's vaccine requires only one shot, while other authorized vaccines require two.

"The faster we can get everybody vaccinated, the lower the chance for mutations and variants," Gorsky said in a CNBC interview.

COVID-19 Vaccine

Frequently Asked Questions

How does a vaccine work?

A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.

How many types of vaccines are there?

There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.

What does it take to develop a vaccine of this kind?

Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.

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J&J CEO Alex Gorsky sees COVID-19 shots in American arms in 1-2 days as shipping starts

Gorsky said J&J was confident that its vaccine would have a 'robust response' against these emerging variants, based on its clinical trial in countries including South Africa and Brazil where worrisome variants were circulating.

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