COVID Reinfection Study Shows Why Older Adults Need to Get Vaccinated

If you’ve been infected with COVID-19, your body may have already built some natural immunity to the virus without vaccination. But experts have found this isn’t the case for everyone.

New research published in The Lancet this month found natural immunity after recovering from COVID-19 protected people against reinfection for at least six months—but this effect was not as robust in adults over the age of 65.

The research team discovered only 47% of adults over 65 were protected against reinfection compared to about 80% of younger adults. The results only confirm the urgent need for vaccinating older adults who are already at high risk of developing severe COVID-19 illness and death.

“Our study confirms what a number of others appeared to suggest: reinfection with COVID-19 is rare in younger, healthy people, but the elderly are at greater risk of catching it again,” the study’s senior author Steen Ethelberg, from the Statens Serum Institut, Denmark, said in a press release.

SARS-CoV-2 Reinfection Rates

The researchers tracked Danish patients’ reinfection rates during the second wave of COVID-19 cases from September 1 to December 31, 2020. They collected patient information from the Danish Microbiology database and compared the positive or negative PCR results from throat swab samples collected in the first wave and second wave.

A total of 525,339 people who had gotten tested during the first and second wave of the pandemic were used in the analysis. Approximately 2.11% tested positive for SARS-CoV-2, the virus that causes COVID-19, in the first wave. Of those, 0.65% were reinfected again in the second wave. About 3.3% of patients who tested negative in the first wave, then tested positive in the second.

Researchers calculated that about 80 to 83% of the participants were protected from reinfection. In a separate analysis, researchers found that older adults 65 years and older had lower protection—at 47%—than younger adults. The team did not find a weakening of natural immunity after a 6-month follow-up.

Beyond the current study’s results, there has been other research suggesting people who are immunocompromised may also be at high risk for reinfection.

Can Vaccines Protect Against Reinfection?

MarkAlain Déry, DO, MPH, FACOI, epidemiologist and medical director for infectious diseases at Access Health Louisiana, tells Verywell the currently approved vaccines were designed to protect against infection from the original COVID-19 strain—known as the wild-type virus—that first emerged in Wuhan, China. While he says reinfection is always a possibility, it is exceedingly rare.

However, the situation changes when you include COVID-19 variants into the equation. One of The Lancet study’s major limitations is the lack of testing done on variants of concern. “I would consider it more likely to be reinfected with one of the variants than a wild-type,” Déry says.

The Centers for Disease Control and Prevention (CDC) lists several variants as “concerning” in the U.S. including, the U.K. (B.1.1.7), Brazil (P.1), and South Afric a (B.1.351) variants. There are several mutations on the spike protein of variants that allow for faster transmission, severe disease, and evasion of the immune system.

Fortunately, Déry says, current research suggests the B.1.1.7 variant is unlikely to evade vaccine-induced immunity. “If you got vaccinated with one of the mRNA vaccines or with the Johnson & Johnson vaccine, it’s unlikely for you to be reinfected with the variant,” Déry says.

But the B.1.351 and P.1 variants complicate the situation. There is limited data on how vaccines respond to these strains.

There have also been reports of these variants causing massive COVID-19 reinfections. A January 2021 study in The Lancet found the city of Manaus, Brazil—which had about 76% of its population infected with COVID-19 in October 2020—experienced a resurgence of COVID-19 cases, with 42% of cases coming from the P.1 variant.

“As far as I’m concerned, the most important thing is we don’t know whether or not the variants can escape vaccine-induced immunity,” Déry says. “Everybody right now is at risk until we know more information.”

Vaccination Is Your Best Protection

While scientists continue to learn more about the variants, the good news is vaccinations are still your best shot at preventing illness.

A February 2021 preprint study—meaning it hasn’t been peer-reviewed—in medRxiv estimates that increasing vaccination efforts and implementing partial lockdowns would help limit the spread of variants that could become dominant by the summer.

A new, real-world study published this week from the CDC further confirms two doses of the Pfizer and Moderna vaccines are 90% protective against COVID-19 infection.