46-year-old Edith Arangoitia (who came to accompany her older mother) was born on February 16, 2021 by Dr. Galen Harnden in La Colaborativa in Chelsea, Massachusetts, was vaccinated with the Pfizer-BioNTech Covid-19 vaccine.

Joseph Precious | AFP | Getty Images

The Chief Medical Officer of the White House, Dr. Anthony Fauci said Monday that Americans should continue to receive two doses of the Pfizer and Moderna Covid-19 vaccines, although a recent study in the US showed the shots were highly effective after just one dose.

A study by the Centers for Disease Control and Prevention published last week found that a single dose of the Covid-19 vaccine from Pfizer or Moderna was 80% effective in preventing coronavirus infections in healthcare workers and other key workers. Two doses are better than one, federal health officials said, adding that the vaccines’ effectiveness rose to 90% two weeks after the second dose.

While the 80% figure was good news, Fauci said Monday he was still concerned about the length of protection after a single dose, particularly the emergence of highly contagious variants that have shown they can evade the vaccines’ protection .

“If you look at the level of protection after a dose, you can say it’s 80%, but it’s a little weak 80%,” Fauci said during a White House press conference on the pandemic. “If you leave it at one dose, how long will it take?”

Highly infectious Covid-19 variants that have shown some resistance to vaccines also pose a challenge, Fauci said. “You’re in a weak zone if you don’t get the full effect of two doses,” he said.

Fauci’s comments come as some health experts and public health officials argue that the U.S. should prefer to give Americans just one dose of the vaccines before moving on to a second dose, accelerating the pace of vaccinations across the country.

Unlike the Johnson & Johnson vaccine, which requires one dose, the Pfizer and Moderna vaccines require two vaccinations three to four weeks apart. In the UK, health officials decided to increase the time between the first and second dose to 12 weeks to speed up vaccinations.

Fauci has said repeatedly over the past few months that the US should stick to the two-dose regime.

Dr. Paul Offit, a voting member of the FDA’s Vaccines and Related Biological Products Advisory Committee who reviewed both Pfizer and Moderna’s vaccines for emergency approval, told CNBC last week that studies showed immunity after the second dose actually appears to be “more permanent”, meaning that protection can last longer.

The two-dose vaccination schedule also produces ten times the amount of neutralizing antibodies, which play an important role in fighting the virus, from the first dose to the second, Offit told CNBC.

Second, and more importantly, after the second dose, scientists also discovered what are known as T cells, another important part of the immune response that usually provides longer-lasting immunity, he said.

Fauci said Monday he “respects” the case for a one-dose strategy, but added that the US currently has enough doses to provide Americans with the first and second dose. “Although we always stay open, we consider the route we are on to be the best route,” he said.