Experts Say It’s Unlikely Fully Vaccinated People Are Unknowingly Spreading COVID-19

  • Those who previously had COVID-19 may wonder how strongly they are protected from the delta variant.
  • Natural immunity does, in many cases, protect people from reinfection. And when they do occur, they tend to be mild.
  • Due to the unknowns, some experts are advising people who have had COVID-19 to get one dose to boost their antibody levels.

The Centers for Disease Control and Prevention (CDC) announced this week that delta is now the most dominant variant in the United States, accounting for approximately 51 percent of all new cases.

PfizerTrusted SourceModernaAstraZeneca, and Johnson & Johnson vaccines work well against the variants, including delta, especially when it comes to preventing severe illness, hospitalization, and death.

But those who previously had COVID-19 may wonder how strongly they are protected from acquiring the delta variant.

Immunity after a previous infection does, in many cases, protect people from reinfection. And when it does occur, the illness tends to be mild.

But immunity varies significantly from person to person, so while many people mount a strong, durable immune response that protects them against delta after a previous infection, some may generate a weak immune response and remain at risk.

Due to the unknowns, some experts are advising people who have had COVID-19 to get at least one vaccine dose to boost their antibody levels.

Others, however, are recommending people who’ve had COVID-19 to get fully vaccinated, either with two doses of a messenger RNA (mRNA) shot or the one dose of Johnson & Johnson’s vaccine.

Reinfection remains rare

“We know that reinfection is not a common occurrence, at least in the short term with the original variant of the virus as well as some of the other variance,” said Dr. Amesh Adalja, a senior scholar at Johns Hopkins Center for Health Security and an infectious disease expert.

study from the Cleveland Clinic that tracked cases in healthcare workers who were either vaccinated or previously had COVID-19 found that the rate of reinfection is essentially the same as if they had been vaccinated.

Another studyTrusted Source from Qatar similarly found that the chance of reinfection is similarly low among those who previously had COVID-19 and those who were vaccinated.

Though these studies show reinfection with variants is rare, it’s important to note they were conducted earlier this year and were not conducted in locations with a high circulation of the delta variant.ADVERTISEMENT

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Reinfections tend to be mild

There have been reinfections, and immune responses vary from person to person.

While one person may have produced strong, long-lasting immunity after contracting the coronavirus again, another may have generated a weaker immune response.

Immunity after a previous infection “is highly variable from one person to the next — it may be barely present and not last for long for some persons,” said Dr. Richard A. Martinello, a Yale Medicine infectious diseases specialist and associate professor at Yale School of Medicine.

small study led by researchers at the University of Oxford found that people who produced weaker immune responses may be more at risk for reinfection from new variants.

But in most cases, the immunity conferred from the previous infection appears to provide good protection against severe illness.

“It’s generally the rule that reinfections are not going to be severe because of the preexisting immunity that exists,” Adalja explained.

Our immune system involves many working parts: antibodies, T cells, and B cells.

Antibodies are the body’s first line of defense against infection and go after the spike protein (where the mutations in the variants are occurring).

Antibodies are our ticket to preventing even mild infections.

T cells and memory B cells quietly live in our lymph nodes and spring into action upon being reexposed to a pathogen.

T cells can recognize many different parts of SARS-CoV-2 (at least 57 locations), not just the spike protein that has made so many headlines.

T cells are critical in attacking the virus and preventing severe illness, hospitalization, and death.

Also, a recent report evaluating previous SARS-CoV-2 infections found that memory B cells produce new antibodies that can recognize the new variants and their mutations upon exposure to the pathogen.

Because of the complexity of our immune system, the vast majority of reinfections — even with delta — are expected to be mild.

Doctors still recommend getting vaccinated 

Adalja is recommending the one-dose strategy.

“I advise people who have had a prior infection to get vaccinated. Just one dose may be enough in the subgroup to fortify their natural immunity,” Adalja said.

Evidence shows that just one dose after a previous infection can boost antibody levels even higher than two doses in people who didn’t have a previous infection.

But because of the variability in immunity from person to person, Martinello says the full vaccination course is still recommended.

“Those who have had COVID should get vaccinated and should get the full course of the vaccine they choose,” Martinello said.

Studies have shown that the vaccines work against the variants. Scientists, however, are still learning about immunity in people who had COVID-19.

“Vaccination produces a strong immune response and provides excellent protection against COVID,” Martinello said.

The bottom line:

People who previously had COVID-19 are wondering how strongly they are protected from the delta variant. Studies have shown that, in general, reinfection is rare due to the complex nature of our immune systems. The vast majority of reinfections that have occurred have been mild. Immunity from a previous infection does provide some level of protection. Still, due to the unknowns, infectious disease doctors recommend people who have had COVID-19 get either one dose to boost their antibodies or get fully vaccinated.


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