Los Angeles—Clinical studies continue to call into question the need for many COVID-19 survivors to receive more than one dose of mRNA vaccines for novel coronavirus.

That has special significance with a pause in use of one of the COVID-19 vaccines—the viral vector vaccine from Johnson & Johnson—receiving emergency-use authorization from the FDA.

An article in the journal Nature Medicine makes the argument that a single dose of the Pfizer-BioNTech vaccine for previous COVID-19 patients generates an immunologic response similar to that of individuals receiving the two-dose recommended sequence.

“Our findings extend those from smaller studies reported elsewhere and support a potential strategy of providing a single dose of vaccine to persons with a confirmed prior history of coronavirus infection, along with two doses for people not previously infected,” said Susan Cheng, MD, MPH, MMSc, associate professor of cardiology and director of Public Health Research at the Smidt Heart Institute at Cedars-Sinai. “This approach could maximize the reach of a limited vaccine supply, allowing potentially millions more people to be vaccinated in the U.S. alone.”

The vaccine that was studied, produced by Pfizer Inc. and BioNTech SE,  is normally administered in two doses, 21 days apart, to provide nearly full protection against the novel coronavirus, known as SARS-CoV-2.

The Cedars-Sinai research strongly suggests the second dose, designed to be administered 21 days apart to provide full protection against SARS-CoV-2 infection, might not actually be needed for those who successfully recovered from a prior coronavirus infection.

“Overall, individuals who had recovered from COVID-19 developed an antibody response after a single vaccine dose that was comparable to that seen after a two-dose vaccination course administered to individuals without prior infections,” explained Kimia Sobhani, PhD, medical director of the clinical core laboratories and associate professor of Pathology and Laboratory Medicine at Cedars-Sinai. “It appears that a single booster dose given to previously infected individuals offers the same benefit as two doses given to people without prior infection.”

In a cohort of 1,090 healthcare workers receiving the vaccine, researchers observed that spike-specific IgG antibody levels and ACE2 antibody-binding inhibition responses elicited by a single vaccine dose in 35 individuals with prior SARS-CoV-2 infection were similar to those seen after two doses of vaccine in 228 individuals without prior infection. In addition, postvaccine symptoms were found to be more prominent for those with prior infection after the first dose, although symptomology was similar between groups after the second dose.

“Challenges to the supply chain have prompted queries around whether single-dose administration rather than double-dose administration might suffice for certain individuals, including those recovered from prior infection,” the authors point out.

“Emerging immune data, including detectable presence of anti-SARS-CoV-2 antibodies and virus-specific T cells, have suggested possible alternate vaccination strategies for previously infected individuals.”

They note that recent small studies “have indicated that individuals with prior infection might have naturally acquired immunity that could be sufficiently enhanced by a single dose rather than a double dose of administered vaccine.”

For the current study, researchers measured antibody levels at three time points: before or up to 3 days after dose 1; within 7–21 days after dose 1; and within 7–21 days after dose 2.

Antibody levels were measured only up to 21 days following each vaccine dose; the authors suggest that longer-term follow-up likely would provide additionally informative data, especially regarding the duration of the immunity acquired from receiving a single versus double dose of the vaccine. They also called for larger cohort samples, and studies to determine if similar results would occur with other COVID-19 vaccines.

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