One Vax Dose and Done? Evidence Mounts in Previously Infected

People with previous COVID-19 infection had higher antibody levels after one dose of Pfizer vaccine compared with uninfected people after two doses, a small lab study of 59 people showed.

Not only that, but IgG levels did not increase after the second dose among those previously infected, which could indicate that one dose of vaccine may be sufficient for this population, reported James Moy, MD, of Rush University Medical Center in Chicago, and colleagues.

“This study highlights the potential for recommending a single dose for previously infected individuals and may be useful for discussions surrounding vaccination strategy,” the authors wrote in a JAMA Network Open research letter.

Offering one dose of vaccine instead of two to those previously infected with COVID-19 is hotly contested, with some experts conceding it’s likely that previously infected individuals only need one dose, but that it would be challenging from a programmatic standpoint.

Indeed, Moy’s group urged performing “baseline serological testing” for previously infected individuals, but CDC and the agency’s Advisory Committee on Immunization Practices (ACIP) argued that this would be next to impossible to do for the entire country.

At a meeting back in March, ACIP Chair José Romero, MD, who is also director of the Arkansas Department of Health, was concerned that the one-dose strategy would only work if individuals had adequate or high antibody titers. However, if people had no antibodies or low antibodies, they may not have “enough memory B-cells to boost to levels that will be protective,” he said.

Moy and colleagues recruited adult participants at the team’s academic medical center, and divided them based on infection status. Prior infection was determined by a positive RT-PCR test and/or a positive SARS-CoV-2 antibody result. Overall, 30 participants had no evidence of infection, while 29 did.

The authors measured SARS-CoV-2 spike IgG levels at baseline and then following one and two doses of the Pfizer vaccine among all participants.

The 59 participants had a mean age of 42, almost three-quarters were women, and 49% were white. Mean IgG differences between the first and second dose were non-significant in previously infected individuals. Interestingly, four participants reported a previous positive COVID-19 test via RT-PCR, but had no evidence of antibodies.

“Vaccine responses in these four participants resembled infection-naive individuals,” Moy’s group noted, adding that because this group did not develop S-protein antibodies, baseline testing should be required before forgoing a second dose.

Limitations to the data, the researchers said, included the small sample size and lack of diversity of participants, as well as lack of neutralization studies and T-cell response studies.