Pfizer, Moderna may reduce risk of asymptomatic Covid infection

Pfizer, Moderna may reduce risk of asymptomatic Covid infection
WASHINGTON: Patients without Covid-19 symptoms are much less likely to test positive, and unknowingly spread Covid-19 ten days after receiving a second dose of a messenger RNA vaccine, compared to those who have not been vaccinated, one study says.
Researchers at Mayo Clinic in the US noted that several vaccines are now clinically available under emergency approval and have shown efficacy against symptomatic Covid-19.
However, the impact of vaccines on asymptomatic SARS-CoV-2 infection is largely unknown, they said.
The Pfizer BioNTech and Moderna messenger RNA (mRNA) vaccines for Covid-19 are approved for emergency use in many countries.
An mRNA vaccine is based on the segments of the genetic material, or RNA, of the novel coronavirus.
With two doses of a Covid-19 mRNA vaccine, people without symptoms showed an 80 percent lower adjusted risk of testing positive for the disease after their last dose, the researchers said.
The findings, published in the journal Clinical Infectious Diseases, underscore the efficacy of Covid-19 mRNA vaccines to significantly limit the spread of Covid-19 in people without symptoms who could unwittingly spread the infection to others.
“We found that those patients with no symptoms who received at least one dose of the first authorized mRNA Covid-19 vaccine, Pfizer-BioNTech, 10 days or more prior to screening were 72 percent less likely to test positive,” said Aaron Tande, a Mayo Clinic infectious disease specialist and co-lead author of the article.
"Those who received two doses were 73 percent less likely, compared to the unvaccinated group," said Tande.
After adjusting for a range of factors, researchers found an 80 percent risk reduction in testing positive for Covid-19 in those with two doses of a Covid-19 mRNA vaccine.
The researchers retrospectively looked at a cohort of 39,000 patients who underwent pre-procedural molecular screening tests for Covid-19.
More than 48,000 screening tests were conducted, including 3,000 in patients who received at least one dose of an mRNA Covid-19 vaccine, they said.
According to the researchers, these screening tests were part of routine Covid-19 tests prior to treatments not related to Covid-19, such as surgeries and other procedures.
Patients in the vaccinated group had received at least one dose of a messenger RNA Covid-19 vaccine, they added.

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