Do COVID-19 Survivors Need Only 1 of a 2-Dose Vaccination?

Survivors of COVID-19 were found to have a stronger immunologic response to the first dose of the 2-dose vaccines against SARS-CoV-2 than those not previously infected, suggesting to the investigators that the second dose could be conserved for those who have not had the illness.

"Current shortages in COVID-19 vaccine production and distribution have led some experts to suggested untested regimens," observed Saman Saadat, PhD, Institute of Human Virology, University of Maryland School of Medicine, Baltimore, MD, and colleagues.

"However, neither recall responses nor ideal vaccine dosing regimens have been studied in those previously infected with SARS-CoV-2," they noted.

To ascertain whether previous infection might essentially serve in lieu of 1 dose, fostering adequate protective immunity and memory responses from the first dose of the 2-dose vaccines, they compared response to the first dose in healthcare workers with or without previous infection and between those who experienced symptoms or had been asymptomatic.

Saadat and colleagues identified 59 participants who were separated into 3 groups: 17 who were Sars-CoV-2 IgG-antibody negative (Ab-negative),16 who previously had COVID-19 without symptoms (asymptomatic), and 26 who had experienced COVID-19 with symptoms (symptomatic).Blood draws were performed at baseline, and on days 7 and 14 after vaccination with the first dose of either the Pfizer-BioNTech or Moderna 2-dose vaccines.

The plasma was tested for IgG to spike titer, measured as half-maximal binding titer.The reciprocal half-maximal binding titer, the investigators explain, represents the dilution of plasma that achieves 50% of maximal binding of a known control that reaches saturation.In addition, samples were tested for the 99% inhibitor dose (ID99), the highest dilution at which 99% of cells were protected by virus neutralization.

The investigators reported that at days 0, 7 and 14, the median reciprocal half-maximal binding titers were higher in each of the asymptomatic and symptomatic groups compared with the Ab-negative group. At days 0 and 14, the median reciprocal ID99 virus neutralization titers of each of the symptomatic and symptomatic groups were also higher than the Ab-negative group.

"Healthcare workers with previous COVID-19 infection, based on laboratory-confirmed serology testing, had higher antibody titer responses to a single dose of mRNA vaccine than those who were not previously infected," they reported.

Co-senior author Anthony Harris, MD, Department of Epidemiology and Public Health, University of Maryland School of Medicine discussed the implications of their findings with Contagion.

"We believe that COVID-19 survivors should only get one dose of (an) mRNA vaccine made by Pfizer and Moderna, which would speed the rate of immunization by allowing others to get these additional doses," Harris said.

Harris also told Contagion his response to comments which had been posted with the publication of the study. To a question from Raffaele Pezzilli, MD, Potenza County Medical Association, Italy, on whether the time interval from prior COVID-19 infection to the vaccination could have been a variable, Harris said, "People included in our study had their original SARS-CoV-2 infection at least six months prior.So we think our results are generalizable to at least 6 months prior, and likely longer."

To the question from Viroj Wiwanitkit, MD, Dr DY Patil University, Pune, India, on whether a new vaccine without long-term data on safety should be given to a person who might not need it because of confirmed previous infection, Harris pointed out that while their results don't address that, they did show, "that people previously infected with SARS-CoV-2 did have baseline antibody levels prior any dose of vaccine."