Single Dose of mRNA Vaccine May be Enough for COVID-19 Experienced People


MN titers showed a striking increase after just 1 dose in experienced subjects.

With the introduction of numerous vaccines, including Janssen’s single shot adenovirus, much talk has surrounded the issue of whether those who previously had an infection with COVID-19 require both doses of the mRNA vaccines. Fully understanding this issue is a public health priority, as more doses could be given out to others if some only require a single dose.

A recent study conducted by investigators from the NYU Infectious Diseases with Public Health Importance (IDPHI) Study Team sought to measure the immune responses before and after mRNA vaccine in people with or without histories of COVID-19. The data was presented during the Conference on Retroviruses and Opportunistic Infections (CROI) 2021 virtual sessions.

The investigators behind the study collected specimens were from participants before and 6 to 14 days after both doses. Humoral assays included an S1-specific Ig enzyme-linked immunosorbent assay (ELISA), as well as a live-virus microneutralization assay (MN) vs the original SARS-CoV-2 USA-WA1/2020 strain. The enzyme-linked immunospot (ELISpot) assays and 36-color spectral analysis flow cytometry assessed B- and T-cell responses.

The study included 33 participants of which 32 received the Pfizer BioNTech vaccine and 1 received the Moderna vaccine. 14 of the participants had a history of COVID-19 and 19 were SARS-CoV-2-naïve.

Findings from the study showed that S1-specific IgG/A/M ASC were detected readily by ELISpot 6 to 14 days after the first dose and were higher in those with a history of COVID-19. However, after dose 2, the converse was observed. S1-specific IgG was present at baseline in experienced subjects, peaked at 6 to 14 days after dose 1, and no boost was observed after dose 2. In naïve participants, S1-specific IgG was not present at baseline, low at day 6 to 14, higher at day 21, and was boosted by the second dose.

Additional findings showed that by 6 to 14 days after dose 2, both experienced and naïve subjects had similar S1-specific IgG titers.

“People with a history of SARS-CoV-2 infection who received a single dose of mRNA vaccine produced binding and neutralizing antibody titers at 6-14 days that were similar to, or higher than, titers in SARS-CoV-2-naïve people who had received 2 doses,” the authors wrote. “Their titers were not boosted by a second dose. These findings support a hypothesis that SARS-CoV-2-experienced people may require only a single dose of mRNA vaccine.”

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