CDC: Vaccine, previous infection offered added protection against delta

Vaccinated people who had previously been infected with COVID-19 and contracted the virus during the delta variant surge last year were better protected against the disease than those who were vaccinated and did not become infected, the CDC reported on Jan. 19.

The findings give new insight into natural immunity against current and potentially upcoming variants.

Researchers also noted that protection specifically against the delta variant was highest among those who were both previously infected with the virus and vaccinated. 

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"During May–November 2021, case and hospitalization rates were highest among persons who were unvaccinated without a previous diagnosis. Before Delta became the predominant variant in June, case rates were higher among persons who survived a previous infection than persons who were vaccinated alone. By early October, persons who survived a previous infection had lower case rates than persons who were vaccinated alone," the CDC wrote. 

Protection against the vaccine was lowest among those who neither received a vaccine or contracted COVID-19, according to CDC researchers.

Despite these findings suggesting the potency of natural immunity, the CDC says getting vaccinated still remains anyone’s best shot at protection from severe illness or death caused by an emerging variant. 

"Although the epidemiology of COVID-19 might change as new variants emerge, vaccination remains the safest strategy for averting future SARS-CoV-2 infections, hospitalizations, long-term sequelae, and death," the CDC wrote. 

These findings do not apply to the newer omicron variant, which now makes up nearly all of COVID-19 cases in the U.S.

"The evidence in this report does not change our vaccination recommendations," Dr. Ben Silk of the CDC and one of the study's authors told a media briefing. "We know that vaccination is still the safest way to protect yourself against COVID-19," he added.

On the topic of reinfection: Vaccines versus natural immunity

Studies have shown that infection from COVID-19 provides short-term immunity, but that protection fades over time. In addition, natural immunity differs from person to person. Even those who have had COVID-19 can benefit from the vaccine because it boosts existing immunity.

So far, misleading claims surrounding natural immunity spread on social media, but these claims vary slightly. 

Some raise questions whether the vaccine will make any difference for those who have already had COVID-19, and others suggest that natural immunity is better than receiving the vaccine.

But this is not the case, according to a CDC report published in August 2021. The report highlights a study that found those who were infected with COVID-19 but never vaccinated had a higher risk of reinfection than those who had been vaccinated. The study, conducted in Kentucky, examined residents with lab-confirmed infections in 2020.

Other studies have shown that those who were previously infected with COVID-19 and received the vaccine made antibodies that could identify variants even without being exposed to the variant.

For those who have had the virus and are thinking of not getting the vaccine, experts caution that having COVID-19 does not guarantee antibodies, while the vaccines have been shown to offer protection against serious infection, hospitalization and death.

David Boulware, an infectious disease specialist at the University of Minnesota, said he generally recommends that people with prior infection receive at least one dose of vaccine.

"There is short-term protection after prior infection which lasts for multiple months. The duration is variable, likely based on the severity of prior infection," he said in an email. "A second exposure by the immune system will boost long-term memory immune cells (memory B and T cells) that live for decades."

The Associated Press contributed to this story.