In-Depth: Why many breakthrough infections look more like allergies than COVID

Black Woman Working from Home And Sneezing For Cold, flu, sick, computer work
Posted at 7:57 AM, Sep 18, 2021

SAN DIEGO (KGTV) -- Doctors say people fully vaccinated against COVID-19 should pay attention to symptoms they might otherwise dismiss as allergies. They could be signs of a breakthrough infection.

Recent studies show vaccinated people tend to have different symptoms than the ones most people commonly associate with the disease. Instead of persistent coughing, fever, or shortness of breath, the vaccinated tend to have symptoms of a head cold like sneezing, if they develop symptoms at all.

“That is the new symptom in town for 2021,” UC San Francisco infectious disease expert Dr. Peter Chin-Hong said.

Sneezing wasn’t associated with COVID early in the pandemic, Dr. Chin-Hong noted.

“We said if you are sneezing, don’t worry about it. It’s definitely not COVID. Don’t go out and use up a bunch of tests. Now we’re realizing that people who thought they had allergies actually have breakthrough COVID,” he said.

To be clear, people who are vaccinated are five times less likely to get infected in the first place, according to a Centers for Disease Control and Prevention study that examined data in Los Angeles County. The vaccinated are 30 times less likely to develop hospital-level disease.

But in the unfortunate event someone does get a breakthrough infection, researchers at King’s College London found sneezing is the third most commonly reported symptom by vaccinated people, behind headache and runny nose.

A study in The Lancet analyzed responses to a smartphone app survey from 900 fully vaccinated people who had a breakthrough infection. They found infections in the fully vaccinated were 43 percent less likely to involve coughing and 73 percent less likely to result in fever than infections in the unvaccinated.

Doctors say the diverging symptoms by vaccine status make sense when you consider how the virus enters the body and how the body responds.

In most cases, the virus enters through the nose. In the unvaccinated, people have relatively few defensive cells that recognize the new pathogen. If the virus is unchecked, it can infiltrate deep into the body, tripping last-ditch security systems that cause fever and inflammation in the lungs.

By contrast, the vaccinated have immune defenses at the ready. If the virus slips past the first line of antibodies in a vaccinated person’s nose because of waning immunity, there are other cells trained and ready to respond. T cells rush in to eliminate infected cells and rouse reinforcements. B cells churn out more antibodies.

The result is that the immune defenses in a vaccinated person can blockade the virus in the nose before it spreads.

“It’s basically confining the virus to the doorstep of the body where you’re getting first exposed,” said Dr. Christian Ramers of Family Health Centers of San Diego.

Ramers said the delta variant might also play a role. The variant replicates about 1,000 times faster in an infected person’s nose than the original virus. That might prompt a more aggressive blitz of immune cells to the nose.

It’s that rush of responding immune cells that cause blood vessels to expand and trigger sneezing, Chin-Hong explained.

Doctors are noticing the vaccine makes a difference for long COVID too. The study in The Lancet found vaccination reduced the odds of prolonged symptoms by about 50 percent. (The authors defined prolonged symptoms as those lasting 28 days or more.)

Based on other studies, that suggests about 5 to 15 percent of breakthrough infections have prolonged symptoms. The rate of long COVID varies by study, but it’s thought to occur in about 10 to 30 percent of infections of the unvaccinated, Ramers said.

Experts say it’s too soon to tell if the vaccinated and unvaccinated experience different longhaul symptoms, but Chin-Hong suspects they do.

The results of a small study in Israel suggested there were fewer symptoms like brain fog in breakthrough long COVID, Chin-Hong said.

Instead, the vaccinated tended to experience fatigue or loss of smell, two symptoms that can develop after many infections. Most returned to work within a matter of weeks, Chin-Hong noted.