A controversial new paper based on laboratory experiments suggests a possible explanation for why some COVID-19 survivors still test positive on viral RNA tests months later.
Small fragments of genetic instructions from the coronavirus might get integrated into infected cells' genome.
In the experiments, the fragments that got inserted into the cell's genetic code came mainly from the tail-end of the viral genome and cannot induce the cell to create infectious virus. However, they might be enough to trigger a positive result on COVID-19 PCR tests.
"There is no evidence that the process of these integrations into the genome causes harm," said study leader Rudolf Jaenisch of the Whitehead Institute for Biomedical Research at MIT, adding that the researchers believe that is very unlikely.
Other experts have said the findings, reported in the journal PNAS, likely reflect unintended effects of experimental methods.
The researchers have so far seen the phenomenon only in test tubes. They are trying to find direct evidence for SARS-CoV-2 sequences integrated into the genome in patients, "but these experiments are technically very challenging," Jaenisch said.
The vaccines from Pfizer/BioNTech and Moderna use messenger RNA to teach cells to make a protein that resembles a site on the virus. But the cell quickly breaks down the RNA and gets rid of it.
"There is no evidence that vaccine RNA could integrate and we believe that this is highly unlikely," Jaenisch said.
The high risks of complications from COVID-19 "would be a very strong incentive to get the vaccine," he said, citing negligible risk from the shots.