Could COVID-19 immunity last decades? Here’s the science.

Illustration of b cells and antibodies
(Image credit: Shutterstock)

The body builds a protective fleet of immune cells when infected with COVID-19, and in many people, those defenses linger for more than six months after the infection clears, according to a new study.

The immune cells appear so stable, in fact, that immunity to the virus may last at least several years, the study authors said. "That amount of [immune] memory would likely prevent the vast majority of people from getting hospitalized disease, severe disease, for many years," co-author Shane Crotty, a virologist at the La Jolla Institute of Immunology in California, told The New York Times, which first reported on the study.

That said, making predictions about how long immunity to the coronavirus lasts can be "tricky," Nicolas Vabret, an assistant professor of medicine at the Mount Sinai Icahn School of Medicine, who was not involved in the study, told Live Science.

"It would be surprising to see the ... immune cells build up in patients over six months and suddenly crash after one year," Vabret said in an email. But "the only way to know whether SARS-CoV-2 immunity will last decades is to study the patients over the same period of time." 

In other words, we won't know exactly how long immunity lasts without continuing to study those who have recovered from COVID-19. However, the new study, posted Nov. 16 to the preprint database bioRxiv, does provide strong hints that the protection is long-lived — although clearly not in all people, as there have been several cases of individuals being reinfected with the coronavirus after recovering. 

Related: 20 of the worst epidemics and pandemics in history 

The research dives into the ranks of the human immune system, assessing how different lines of defense change after a COVID-19 infection. 

These defenses include antibodies, which bind to the virus and either summon immune cells to destroy the bug or neutralize it themselves. Memory B cells, a kind of white blood cell, "remember" the virus after an infection clears and help quickly raise the body's defenses, should the body be reexposed. Memory T cells, another kind of white blood cell, also learn to recognize the coronavirus and dispose of infected cells. Specifically, the authors looked at T cells called CD8+ and CD4+ cells.

The authors assessed all these immune cells and antibodies in 185 people who had recovered from COVID-19. A small number of participants never developed symptoms of the illness, but most experienced mild infections that did not require hospitalization. And 7% of the participants were hospitalized for severe disease. 

The majority of participants provided one blood sample, sometime between six days and eight months after the onset of their infections. Thirty-eight participants gave several blood samples between those time points, allowing the authors to track their immune response through time.

Ultimately, "one could argue that what they found is not so surprising, as the immune response dynamics they measure look like what you would expect from functioning immune systems," Vabret said. 

The authors found that antibodies specific to the spike protein — a structure on the surface of the virus — remain stable for months and begin to wane about six to eight months after infection. At five months post-infection, nearly all the participants still carried antibodies. The volume of these antibodies differed widely between people, though, with an up to 200-fold difference between individuals. Antibody counts normally fall after an acute infection, Vabret noted, so the modest drop-off at six to eight months came as no surprise.

Related: 11 surprising facts about the immune system

By comparison, memory T and B cells that recognize the virus appear extremely stable, the authors noted. "Essentially no decay of ... memory B cells was observed between days 50 and 240," or eight months later, Marc Jenkins, an immunologist at the University of Minnesota Medical School, who was not involved in the study, said in an email.

"Although some decay of memory T cells was observed, the decay was very slow and may flatten out at some point," Jenkins added. There's reason to believe that the number of memory T cells may stabilize sometime after infection, because T cells against a related coronavirus, SARS-CoV, have been found in recovered patients up to 17 years later, according to a study published July 15 in the journal Nature

Early in the pandemic, scientists raised concerns that immunity to the virus may wear off in about a year; this trend can be seen with the four coronaviruses that cause the common cold, Live Science previously reported. However, studies suggest that the body's reaction to common coronaviruses may differ from that to viruses like SAR-CoV and SARS-CoV-2, which hopped from animals to humans. 

"We don't really know why seasonal coronaviruses do not induce lasting protective immunity," Vabret said. But the new study, along with other recent evidence, suggests that SARS-CoV-2 immunity may be more robust, said Jason Cyster, a professor of microbiology and immunology at the University of California, San Francisco, who was not involved in the study.

That said, a few participants in the new study did not mount long-lasting immune responses to the novel virus. Their transient responses may come down to differences in how much virus they were initially exposed to, or genetics may explain the difference, Cyster said. For instance, genes known as human leukocyte antigen (HLA) genes differ widely between individuals and help alert the immune system to foreign invaders, Live Science previously reported

These inherent differences between people may help explain cases of COVID-19 reinfection, which have been relatively rare but are increasing in number, Science Magazine reported.

Again, to really understand how long COVID-19 immunity lasts, scientists need to continue to study recovered patients. "Certainly, we need to look six months down the road," and see whether the T and B cell counts remain high, Cyster said.

Should immunity be long-term, one big question is whether that durability carries over to vaccines. But natural immunity and vaccine-generated immunity cannot be directly compared, Vabret noted. 

"The mechanisms by which vaccines induce immunity are not necessarily the same as the ones resulting from natural infection," Vabret said. "So the immune protection resulting from a vaccine could last longer or shorter than the one resulting from natural infection."

For example, the Pfizer and Moderna vaccines use a molecular messenger called mRNA to train the body to recognize and attack the coronavirus. No mRNA-based vaccine has ever been approved before, so "we practically know nothing about the durability of those responses," Cyster said.

"I think [that's] the big unknown for me, among the many," he said.

But while some unanswered questions remain, the main takeaway from the new study is that "immune memory to SARS-CoV-2 is very stable," Jenkins said. And — fingers crossed — perhaps those hopeful results will hold well into the future.

Originally published on Live Science. 

Nicoletta Lanese
Channel Editor, Health

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.

  • Chem721
    From the article, quoting from Nicolas Vabret, an assistant professor of medicine at the Mount Sinai Icahn School of Medicine, who was not involved in the study:

    "The mechanisms by which vaccines induce immunity are not necessarily the same as the ones resulting from natural infection," Vabret said. "So the immune protection resulting from a vaccine could last longer or shorter than the one resulting from natural infection."

    end quote,

    This is significant in that natural infections by the virus provide more antigenic sites in which antibodies can be directed. These sites are not provided by the nucleic acid vaccines, which present only the spike antigens. It will no doubt be instructive to watch what happens with the Chinese vaccine CoronaVax (from Sinovax), which relies on chemically-inactivated whole virus. This is much different and so should be the immune response. Which is better (or worse) remains to be seen.

    Curiously there was no mention in the article about mutations of the virus, an active area of research to monitor its changes and how they might negatively impact the current vaccine, and even antibody test kits. This has also raised concerns about changes of the virus from mink farms, and other possible inter-species infections and transmissions.

    It would seem rather obvious that memory of the initial virus without mutations is most important regarding long lasting immunity. The only variable in its return seems mutation, since so many other viruses engage in similar activities to reappear - e.g. colds, and flu.. The rate of mutation of this virus over time will almost certainly play a significant role in immunity conferred by any vaccine or a natural infection. Which is all the more reason to stop it quickly. or rather more quickly than we are. The virus cannot mutate without replication. Allow mutations to continue, and the risk to those previously protected, or soon to be protected by a vaccine, might increase. Many of these viruses behave in a similar fashion. Watch the mutation rate.
  • Allermetrix
    Chem721 said:
    This is significant...
    It is only significant if it is true. And it is unlikely to be true.
    The rRNA used to create the mRNA vaccines is taken from the original genome sequence of SARS-CoV-2. Why should it be any different than the CoV virions itself?
    Mutations are expected but why is it a big concern or yours? Viruses mutate. That is what they do. It is rare that they mutate to a new strain with significant changes in properties. As of today there are no known mutations that will effect the efficacy of the mRNA vaccines. Please stop implying otherwise. We have enough misinformation coming from the anti-vaxxers.
    Why do you think an inactivated virion would be superior to the Pfizer or Moderna mRNA? Do you want your immune system to unnecessarily fend off the other 27 non-neutralizing proteins? Why put the patients at risk of an adverse reaction to these unnecessary proteins. It is believed by some that the nucleocapsid protein may be responsible for short circuiting the complement cascade and killing patients. So why would you want to expose the patients to a non-neutralizing protein that may cause harm?
    There has been NO FINDINGS that would indicate that the mRNA vaccines are less effective than a natural infection. On the other hand there are reports indicating that the vaccins have a higher efficacy than natural infection.
    I do agree it is in everyone's best interest to get vaccinated and rid the Earth of this disease before it does mutate to a strain that the current vaccines cannot neutralize.
    I also highly recommend that 2 weeks after the second shot that everyone get a quantitative antibody test for the S1 and RBD proteins. A qualtative test would be useless, it MUST be a quantitative test. This may give a benchmark for predicting the longevity of the vaccine's durable immunity. AT a minimum it will give peace of mind that you very likely have durable immunity, or not.
  • Allermetrix
    admin said:
    Of course, rare cases of reinfection show that immunity is not long-lasting for everyone.

    Could COVID-19 immunity last decades? Here’s the science. : Read more
    There are no cases or reinfection from symptomatic CoV patients. There is no evidence that the so called reinfections of asymptomatic patients actually were previously infected with CoV. Please stop spreading this misinformation. If it did not come from a peer reviewed study published, in print, in a reputable journal, it is not true.