Why People With COVID Booster Shots Test Positive for Longer

People who are vaccinated and boosted may be more likely to remain COVID-positive after five days of symptom onset if they get sick, according to a preprint study. This means they might still test positive after the five-day isolation period recommended by the Centers for Disease Control and Prevention (CDC).

Michael Mina, MD, PhD, chief medical officer at eMed and co-author of the study, said these results may be misinterpreted to suggest that the COVID-19 vaccines induce a lengthier infection, but this isn’t the case.

Instead, the vaccines prompt the body’s immune system to recognize the virus earlier, so that it can start fighting against the infection right away.

“A fever is actually the human response to try to suppress viral replication because the virus doesn’t like to grow in high temperatures,” Mina told Verywell. “You might get congestion and have a headache. And these are all part of the immunological response, or, or secondary effects of it. But that doesn’t mean that you have a high viral load yet.”

Boosted individuals might recognize their symptoms earlier and start to self-isolate before they’re infectious. But the researchers suggested that there is now a longer gap between developing symptoms and reaching peak viral loads for vaccinated and boosted people.

“You can have symptoms that occur from the immune response, or you can have symptoms occur because the virus is harming you,” he said. “This, unfortunately, got very, very confused by most scientists at the beginning of the pandemic.”

Time Frame of Infectious Period

When people test positive for COVID-19, the progression of their viral loads follows a curve that mimics a mountain with a steep uphill climb, a peak, and a gradual decline at the end, Mina said.

The starting base of the mountain indicates someone’s initial exposure to the virus. Unvaccinated people tend to develop symptoms in the middle of the curve, toward the peak, according to Mina.

But those who are vaccinated often develop symptoms shortly after exposure, as the viral load is on its way uphill. This is because vaccine-induced immunity teaches people to recognize the virus early, which explains the earlier appearance of symptoms, Mina explained.

He added the duration of infectivity remains the same for boosted people, but their body is more alert to the virus. “It’s your immune system that’s creating that awareness, which we should actually see as a good thing,” Mina said.

Symptoms as a Warning Sign

A positive but asymptomatic COVID-19 case could be more dangerous to public health than someone who is symptomatic but testing negative, Mina said. The former was of particular concern before vaccines were available, he added.

“What would happen is people would become infectious before they had any symptoms, and that was a massive problem,” Mina said. “About half of the people never developed symptoms and they still were able to transmit. And that’s because their immune system never had a chance to really turn on.”

Before people had access to vaccination, any display of symptoms was extremely dangerous, Mina added. “It was literally the symptoms of the virus destroying you,” he said.

COVID-19 remains a deadly virus and its symptoms are still not something to be taken lightly. However, at least 66% of the U.S. population is now fully vaccinated and many have developed some form of natural immunity.

As a result, mild COVID-19 symptoms show that our immune system is working to protect us. “Now, our body doesn’t have to wait until the virus is really doing damage to us, for us to recognize, ‘I might be infected,’” Mina said.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.