In an interview with a conservative talk show host, Mr Johnson suggested that the push from health officials for everybody to get inoculated against the novel virus was unnecessary.
"Because it's not a fully approved vaccine, I think we probably should have limited the distribution to it to the really vulnerable," Mr Johnson said. "What is the point? If the science tells us the vaccines are 95 per cent effective. So, if you have a vaccine, quite honestly, what do you care if your neighbour has one or not?"
The lawmaker, who contracted and recovered from Covid-19 in the fall, went on state that he didn't believe he needed a vaccine and didn't understand the “big push to make sure everybody gets the vaccine”.
When responding to the comments on MSNBC on Friday, Dr Fauci was quick to point out hundreds of thousands of reasons why Americans should want to receive a vaccine.
"There's a pretty good reason. We have 567,000 people who've died so far in this country from this disease. That is a really, really good reason to get people vaccinated with a vaccine that you've shown is highly efficacious and quite safe," Dr Fauci said. "And that's the reason for the emergency use authorisation."
Dr Fauci, who serves on the White House Covid-19 Response Team, went on to state that the country was currently living in an "emergency," which was why vaccinations have become so prevalent.
"How can anyone say that 567,000 dead Americans is not an emergency?" he said.
Health experts have pushed a mass vaccination effort in the US in order to lower infection, hospitalisation, and death rates from Covid-19.
More than 141 million Americans, or 42.1 per cent of the country's population, have received at least one dose of a Covid-19 vaccine – with 29.1 per cent of the population fully vaccinated against the novel virus. But health experts like Dr Fauci previously estimated the country would need to vaccinate 70 to 85 per cent of the population to reach herd immunity.
Mr Johnson has further defended his comments after it sparked backlash on Friday.
"Everyone should have the right to gather information, consult with their doctor and decide for themselves whether to get vaccinated," the senator said.
"It is a legitimate question as to whether people at very low risk of suffering serious illness from Covid, particularly the young and healthy, should be encouraged to take a vaccine that is being administered under an Emergency Use Authorisation – in other words, before it has been fully tested and fully approved," he added.
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