CHICAGO — When someone gets a COVID-19 vaccine, it triggers an immune response that will help them fight the virus that causes the deadly disease.
But could it also lead to a false positive if someone is tested after they’re vaccinated?
Northshore University Health System pathologist Dr. Karen Kaul said the COVID-19 vaccines from Pfizer and Moderna both work differently than traditional vaccines.
“It is a messenger RNA vaccine, so unlike old vaccines that inject either an inactivated virus or a piece of viral protein, what this does is inject a little snippet of viral RNA which is taken up in the muscle and into the cells to help us make antibodies,” Kaul said.
For years, people have been taking the flu vaccine to boost an immune response against the flu virus. But when they take it in a mist form it can elicit a false positive flu test.
“What we have seen with flu mist, there’s a little bit of that inactivated virus still in the nasal area or pharynx,” Kaul said. “So if one samples a patient for an influenza test too soon after they’ve received the flu mist you can pick up the virus and detect it. It will give you a positive PCR.”
Since they use RNA, the COVID-19 vaccines from Pfizer and Moderna are designed differently and do not contain the actual virus, but rather a part of the spike protein in the virus that helps it invade and take hold of healthy cells.
“It’s not the whole virus, it’s not inactivated virus but it’s just a little snippet of viral protein and that will stimulate our bodies to make an antibody response against the antigen,” Kaul said.
Since they work differently, Kaul and other pathologists wondered whether the viral protein, expressed through cells in the body, would trigger a similar false positive test result for Covid among vaccine recipients.
“We’ve actually been looking at that and most of the assays do not target the spike protein; l I can’t tell you all of the assays are free of that potential interaction,” Kaul said.
Like many things with this novel coronavirus, there are no definitive answers but experts hope the Covid tests will be accurate and the vaccine will be effective.