People who have recovered from the novel coronavirus infection may need only one shot as opposed to the recommended two jabs if they are taking the Moderna or Pfizer COVID-19 vaccines, according to a study which suggests ways to minimise doses when supplies are limited.
The yet-to-be
peer-reviewed study, posted in the preprint repository medRxiv, assessed the
antibody responses in 109 individuals with and without documented pre-existing
immunity to the novel coronavirus.
According to the
researchers, including Florian Krammer from the Icahn School of Medicine in the
US, a single dose of mRNA vaccine elicits very rapid immune responses in
individuals already possessing antibodies against the coronavirus from previous
exposure to it.
"For individuals
with pre-existing immunity to SARS-CoV-2 the first vaccine dose likely
immunologically resembles the booster dose in naive individuals," the
scientists wrote in the study.
In the research, the
scientists analysed mRNA vaccines which use segments of the viral genetic
material to enable human cells to make the coronavirus spike proteins.
These proteins train the
immune system of vaccine recipients to fight the actual infectious coronavirus
when their body encounters the pathogen.
The scientists said the
post-vaccine antibody levels in recovered COVID-19 patients are comparable to,
or exceed levels, found in those without prior exposure to the virus who
received two vaccinations.
Another yet-to-be
peer-reviewed study in medRxiv also studied antibody responses to a single dose
of the Pfizer-BioNTech or Moderna vaccines in healthcare workers who had
previously recovered from the infection.
It found that their
antibody levels started peaking at seven days since immunisation, and achieved
higher titers and neutralisation in 14 days compared to volunteers exposed to
the vaccine for the first time.
"Although we did
not have peak titers for these individuals after natural infection, the titers
developed after single vaccination was higher than peak titers in inpatients
and outpatients with COVID-19, similar to what has been described in primary
vaccination after two doses of the spike-based mRNA vaccines," the
researchers wrote in the study.
According to the
scientists from the University of Maryland School of Medicine in the US, the
secondary response occurs through activation of the immune system's memory B
cells.
Based on the findings,
the researchers recommend a strategy of single dose vaccination for patients
who have already had laboratory-confirmed COVID-19.
They said those who have
recovered from the disease can be placed lower on the vaccination priority
list.
Commenting on the two
studies, Eleanor Riley, Professor of Immunology and Infectious Disease at the
University of Edinburgh in the UK, said the findings are "very
reassuring", adding that the vaccines are "very effectively boosting
the immunity induced by infection."
While the two studies
suggest that people who have had laboratory-confirmed COVID-19 infection may
only require one dose of the vaccine, Riley, who was unrelated to the studies,
said incorporating this into a mass vaccination programme may be logistically
complex.
He believes it may be
safer to ensure that everyone gets two doses.
The preprint platfrom,
medRxiv, also cautions that the posted reports are preliminary in nature and
have not been certified by peer review.
"They should not be
relied on to guide clinical practice or health-related behavior," it adds.
Lawrence Young,
Virologist and Professor of Molecular Oncology, University of Warwick in the
UK, believes this question can be resolved with further studies.
"...We should be
doing further studies which look at giving previously infected individuals one
dose of an mRNA vaccine," said Young, who was also unrelated to the two
studies.
"If future work can confirm this high level of immunity post a single mRNA vaccine in this group of individuals, this could become a viable option when there are concerns around vaccine supply," he added in a statement.
The Pioneer
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