Following a two-dose approach remains the best way to defeat the COVID-19 pandemic, using the currently available Moderna and Pfizer vaccines, said Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases and a member of the White House’s COVID-19 Response Team, during a press briefing Monday morning.
Recognizing that demand for the vaccine currently exceeds the U.S.’s supply, Fauci noted that some experts have proposed shifting all efforts towards getting more Americans their first dose, “with less emphasis on the second dose.”
The U.K. has chosen to focus primarily on its residents receiving a first dose of vaccine even if it means delaying receipt of a second dose, but as MedPage Today reported last week, that idea is not universally accepted.
In both of the currently available vaccines, Fauci explained, there’s strong data to show that a “prime boost” or second dose offers a “maximum response of 94%-95% efficacy.”
As to whether it makes sense to at least study if one dose might be enough, Fauci said it’s not an unreasonable suggestion. However, as a practical matter, given the number of subjects needed and the time it would take — “several months” to get a “meaningful answer” — the amount of vaccine that would become available as the study progressed would then make the issue “somewhat of a moot point,” he said.
As for what’s known based on the current research about the efficacy of one dose versus two, Fauci explained that a single dose of either the Pfizer or Moderna vaccine elicits a response “above the threshold of protection” against the “wild-type” virus — the dominant strain in the U.S.
That said, after the second dose or “boost,” which is given 21 or 28 days later depending on the vaccine, the neutralizing antibody response was “10-fold higher. So it went, for example, from one to 100 to well over one to 1,000 in the titer,” Fauci said.
“The reason that’s important, not only because of the height of the response and the potency of the response, but as you get to that level of antibody you get a greater breadth of response and by breadth of response, we mean it covers not only the wild-type and currently circulating virus, but also the variants that we see circulating, particularly the 1.1.7 and the 3.5.1,” he said, referring to the two variants first reported in Great Britain (B.1.1.7) and South Africa (B.3.5.1), respectively.
“So it’s not just a matter of potency; it’s a matter of the breadth of what you can cover,” Fauci stressed.
Additionally, there’s a “theoretical” concern that could potentially become a problem if the U.S. were to shift to a single-dose focused strategy, he said. That is, “if you get a suboptimum response, the way viruses respond to pressure, you could actually be inadvertently selecting for more mutants.”
For these reasons, Fauci said, the “optimum approach” the response team will continue to recommend is to get as many people as possible their first dose of vaccine while also ensuring that people get their second vaccine dose on time.
CDC Director Rochelle Walensky, MD, MPH, noted that as of February 7, there have been 699 confirmed variant cases across 34 states, of which all but nine are B.1.1.7.
Asked by a reporter about whether the number of these variants may be an underestimate given delays in sequencing, Walensky said that over the last 3 weeks, sequencing has increased “about 10-fold. So, as we look more we certainly … anticipate we might find more.”
Fauci also confirmed that “it’s true” that modeling has shown that the B.1.1.7 variant is likely to become the dominant strain in the U.S. by the end of March.
However, he reminded the public that the Pfizer and Moderna vaccines are “quite effective” against this variant.
To that end, he stressed the importance of continuing adherence to public health measures — social distancing, masking, hand washing — and focusing on “get[ting] as many people vaccinated as quickly as we possibly can. That’s the best defense against the evolution of variants.”