Well-Being Georgia

in partnership with

Augusta University of Health

COVID-19 Impact on Georgia Latest Articles

October 16, 2020

Can You Get COVID-19 More Than Once?

Can You Get COVID-19 More Than Once?

Updated on October 16, 2020 at 4:00pm EDT.

News of the first person in North America known to have been reinfected by SARS-CoV-2 recently made headlines and dimmed hopes for herd immunity—which occurs when enough people have antibodies to the coronavirus after being infected to effectively contain its spread.

This report of a previously healthy 25-year-old Nevada man twice sickened by COVID-19 is the fifth reinfection case to be described in medical research. There have also been reports that antibodies to the coronavirus can vanish or dwindle over time.

Now, fears are rising that protective immunity to COVID-19 may not be readily achievable.

Are COVID-19 survivors really at risk of getting it again?

Evidence is growing that reinfection is possible. But we still don’t know how common, likely or significant reinfection may be. The immune system’s interaction with this coronavirus, which was identified only about ten months ago, remains a new field of study.

Scientists suspected early on that people who recover from COVID-19 could be reinfected. That’s the case with most betacoronaviruses, a subtype that includes SARS-CoV-2, according to David Sullivan, MD, a professor of Molecular Microbiology and Immunology at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland.

“From the very beginning, in March, most people were predicting you could get reinfected, as per most betacoronaviruses,” says Dr. Sullivan. “It’s not going to surprise us if people can get it a year later.”

Still, the fact that only five cases of reinfection have been reported worldwide so far could suggest that reinfection is rare. Or perhaps it only rarely comes to researchers’ attention. Surveillance for SARS-CoV-2 remains spotty, so reinfection could be common. We just don’t know yet.

“We are probably severely underestimating the number of asymptomatic reinfections,” wrote Yale immunologist Akiko Iwasaki, PhD, in an editorial published on October 12 in The Lancet along with the report of the Nevada man.

In the case of the Nevada man, the evidence of genuine reinfection was strong. Researchers demonstrated that the viral strain isolated after his second positive test differed genetically from the one he had at first. This suggests he had true separate encounters with separate strains, both of which made him sick. He also tested negative between the two confirmed infections.

But less clear-cut cases of potential reinfection could be due to a long course of infection, inaccurate tests or the possibility that the coronavirus could hide out in the body, then reemerge later.

Indeed, in a May 2020 Korean study of people testing positive twice, researchers were unable to grow live virus out of the “re-positive” samples. Nor could they demonstrate that people testing positive for a second time had infected anyone else.

The role of antibodies
Once the immune system “sees” coronavirus, it takes 1 to 2 weeks for antibodies to form. These proteins recognize virus in bodily fluids, stick to it, and, in some cases, render it harmless, ready to be cleared away by other parts of the immune ystem.

Over time, antibody levels can fall. One small August 2020 study published in Nature Medicine involving people infected with SARS-CoV-2 without symptoms found that many had undetectable antibody levels three months later. Research also suggests that the number of neutralizing antibodies—the most protective kind—dwindles a few weeks after symptoms begin.

But here’s some good news: The body has other ways of defending itself.

T-cells and B-cells also matter
Unlike the innate immune system, which launches a general attack to invading pathogens, the body also has an adaptive, or acquired immune system, which responds to exposure to a specific pathogen.

This adaptive arm, which kicks into action when the innate immune system alone isn’t able to control an infection, includes two types of cells that learn from experience: T-cells and B-cells. Both of these immune cells play important roles in the body’s response to pathogens like SARS-CoV-2.

B-cells are antibody factories, while T-cells support B-cells and kill virus-infected cells outright.

Antibody levels may fall after infection. But T-cells and B-cells that the immune system deployed to fight off the infection (or that a vaccine has taught the body to make) can be stored by the immune system for years, where they remain ready to do battle if the virus ever returns.

There’s already evidence that the body forms strong T-cell responses to SARS-CoV-2. Some people even do this without an antibody response, leading some researchers to predict that measuring T-cells may prove better than measuring antibodies to check for immunity. (Antibody testing used in screening the public is prone to false positives, anyway, in part because positive results could reflect antibodies to some other coronaviruses.)

This protection can be long-lasting. Survivors of the 2003 SARS epidemic were recently reported to retain protective memory T-cells up to 17 years later.

Moreover, some people who have never been infected with SARS-CoV-2 still carry T-cells that react to it. These most likely formed against viruses that cause the common cold. They were similar enough to recognize, at least to some degree, the more serious new coronavirus.

Still, Sullivan warns, we don’t know yet how long SARS-CoV-2-specific memory immune cells might last. “Is it a short-term memory or a long-term memory? We don’t really have enough evidence yet to characterize that,” he says, noting that “we’re successfully one-and-done for many viruses, but not for influenza.”

Other lines of defense
Some research suggests that if reinfection does occur, it may be mild. An August 2020 study of macaque monkeys infected with SARS-CoV-2 published in Science found them immune to a second bout, at least if they encountered it during early recovery. In studies of other types of coronavirus infection in both animals and people, milder infections led to short-lived immunity. Severe ones, meanwhile, including those caused by SARS and MERS, may be associated with longer-lasting protection.

But in two of the world’s five reports of reinfection, people experienced worse symptoms the second time around. The Nevada man was one. He weathered his first bout at home, but the second time, he was hospitalized and required oxygen. It’s unknown whether that was because the second viral strain was more virulent, if he got a high dose of virus the second time or because his immune system reacted to reinfection in a way that led to worse disease.

While scientists continue to investigate and learn more about how SARS-CoV-2 affects the body, vaccines are on the way.

In a July 31, 2020 editorial published by The New York Times, Iwasaki and her fellow Yale immunologist Ruslan Medzhitov, PhD, stated unequivocally that falling antibody counts don’t diminish the odds that we’ll develop a useful vaccine. The scientists have noted that one main advantage of vaccines over the body’s natural immune response is that they can be designed to target virus’ weaknesses.

And we shouldn’t necessarily worry that the Nevada case implies that we’ll need separate vaccines for each strain. As Iwasaki wrote in his October editorial, one vaccine should suffice against all the strains in circulation.

She warned, however, that reinfection cases mean we can’t count on whatever immunity we gain from infection to give us herd immunity. We will need vaccines.

Adjuvants, which are ingredients used in some vaccines, can also be used to bolster the body’s immune response, the Centers for Disease Control and Prevention explains.

Sullivan and his colleagues at Johns Hopkins University are also conducting randomized controlled trials, which are investigating the use of antibody-rich convalescent plasma to treat people with COVID-19. The treatment involves the introduction of antibodies from another person who has recovered from the disease to achieve what’s known as “passive immunity.”

Medically reviewed in October 2020.

Zheng J. “SARS-CoV-2: an Emerging Coronavirus that Causes a Global Threat.” International Journal of Biological Sciences. 2020;16(10):1678-1685. Published 2020 Mar 15.
Chen, Z., John Wherry, E. “T cell responses in patients with COVID-19.” Nature Reviews Immunology. 20, 529–536 (2020).
Glen M. Otto DVM, DACLAM, Charles B. Clifford DVM, PhD, DACVP. “Biology and Diseases of Rats.” Laboratory Animal Medicine (Third Edition). 2015.
Centers for Disease Control and Prevention. “About COVID-19.” Sept. 2020.
Hanyujie Kang, Yishan Wang, Zhaohui Tong, et al. “Retest positive for SARS‐CoV‐2 RNA of ‘recovered’ patients with COVID‐19: Persistence, sampling issues, or re‐infection?” Journal of Medical Virology. June 3, 2020.
Kang YJ. “South Korea's COVID-19 Infection Status: From the Perspective of Re-positive Test Results After Viral Clearance Evidenced by Negative Test Results.” [published online ahead of print, 2020 May 22]. Disaster Medicine and Public Health Preparedness. 2020;1-3.
World Health Organization. “Q&A: Serology and COVID-19.” June 2020.
Long QX, Tang XJ, Shi QL, et al. “Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections.” Nature Medicine. 2020;26(8):1200-1204.
Mayo Clinic. “Herd immunity and COVID-19 (coronavirus): What you need to know.”
University of Minnesota: Center for Infectious Disease Research and Policy. “Study: COVID-19 antibodies decay quickly after mild illness.” July 22, 2020.
Tomas Castro-Dopico, Menna R. Clatworthy. The Immunology of Transplantation. Kidney Transplantation - Principles and Practice (Eighth Edition). 2019.
National Human Genome Research Institute. “Lymphocyte.”
Mitch Leslie. “T cells found in coronavirus patients ‘bode well’ for long-term immunity.” Science. 22 May 2020: Vol. 368, Issue 6493, pp. 809-810.
Daniel M. Altmann and Rosemary J. Boyton. “SARS-CoV-2 T cell immunity: Specificity, function, durability, and role in protection. Science Immunology.” 17 Jul 2020: Vol. 5, Issue 49.
Le Bert, N., Tan, A.T., Kunasegaran, K. et al. “SARS-CoV-2-specific T cell immunity in cases of COVID-19 and SARS, and uninfected controls.” Nature 584, 457–462 (2020).
Alba Grifoni, Daniela Weiskopf, Sydney I. Ramirez. “Targets of T Cell Responses to SARS-CoV-2 Coronavirus in Humans with COVID-19 Disease and Unexposed Individuals.” Cell. Vol 181, Issue 7, P1489-1501. June 25, 2020.
Wei Deng, Linlin Bao, Jiangning Liu, et al. “Primary exposure to SARS-CoV-2 protects against reinfection in rhesus macaques.” Science. Vol. 369, Issue 6505, pp. 818-823. Aug 14, 2020.
Marta Galanti, Jeffrey Shaman. “Direct Observation of Repeated Infections With Endemic Coronaviruses.” The Journal of Infectious Diseases, jiaa392.
Centers for Disease Control and Prevention. “Adjuvants and Vaccines.” Aug 14, 2020.
U.S. National Library of Medicine. ClinicalTrials.gov. “Convalescent Plasma to Limit SARS-CoV-2 Associated Complications (CSSC-004).” Sept. 14, 2020.
The New York Times. “Scared That Covid-19 Immunity Won’t Last? Don’t Be.” July 31. 2020.
Richard L Tillett, PhD, Joel R Sevinsky, PhD, Paul D Hartley, PhD, et al. “Genomic evidence for reinfection with SARS-CoV-2: a case study.” The Lancet Infectious Diseases. Oct 12, 2020.
Akiko Iwasaki. “What reinfections mean for COVID-19.” The Lancet Infectious Diseases. Oct 12, 2020.


COVID-19 Basics