Researchers find declining antibody levels in SARS-CoV-2 patients are offset by T cells and B cells that remain behind to fight off reinfection

Questions remain regarding how long antibodies produced by a COVID-19 vaccine or natural infection will provide ongoing protection against SARS-CoV-2. However, a new study showing COVID-19 immunity may be “robust” and “long lasting” may signal important news for clinical laboratories and in vitro diagnostics companies developing serological tests for the coronavirus disease.

The study, titled, “Immunological Memory to SARS-CoV-2 Assessed for up to 8 Months after Infection,” was published in the journal Science. The data suggest nearly all COVID-19 survivors have the immune cells necessary to fight re-infection for five to eight months or more.

“There was a lot of concern originally that this virus might not induce much memory. Instead, the immune memory looks quite good,” Shane Crotty, PhD, Professor at the Center for Infectious Disease and Vaccine Research at the La Jolla Institute (LJI) for Immunology in California and coauthor of the study, told MIT Review. LJI has an official affiliation agreement with UC San Diego Health System and the UC San Diego School of Medicine.

Retaining Protection from SARS-CoV-2 Reinfection

The LJI research team analyzed blood samples from 188 COVID-19 patients, 7% of whom had been hospitalized. They measured not only virus-specific antibodies in the blood stream, but also memory B cell infections, T helper cells, and cytotoxic (killer) T cells.

While antibodies eventually disappear from the blood stream, T cells and B cells appear to remain to fight future reinfection.

“As far as we know, this is the largest study ever for any acute infection that has measured all four of those components of immune memory,” Crotty said in a La Jolla Institute news release.

The LJI researchers found that virus-specific antibodies remained in the blood stream months after infection while spike-specific memory B cells—which could trigger an accelerated and robust antibody-mediated immune response in the event of reinfection—actually increased in the body after six months. In addition, COVID-19 survivors had an army of T cells ready to halt reinfection.

“Our data show immune memory in at least three immunological compartments was measurable in ~95% of subjects five to eight months post symptom onset, indicating that durable immunity against secondary COVID-19 disease is a possibility in most individuals,” the study concludes. The small percentage of the population found not to have long-lasting immunity following COVID-19 infection could be vaccinated in an effort to stop reinfection from occurring on the way to achieving herd immunity, the LJI researchers maintained.

Do COVID-19 Vaccines Create Equal Immunity Against Reinfection?

Whether COVID-19 vaccinations will provide the same immune response as an active infection has yet to be determined, but indications are protection may be equally strong.

“It is possible that immune memory will be similarly long lasting similar following vaccination, but we will have to wait until the data come in to be able to tell for sure,”

LJI Research Professor Daniela Weiskopf, PhD, said in the LJI statement. “Several months ago, our studies showed that natural infection induced a strong response, and this study now shows that the response lasts. The vaccine studies are at the initial stages, and so far, have been associated with strong protection. We are hopeful that a similar pattern of responses lasting over time will also emerge for the vaccine-induced responses.”

The study’s authors cautioned that people previously diagnosed with COVID-19 should not assume they have protective immunity from reinfection, the Washington Post noted. In fact, according to the LJI news release, researchers saw a “100-fold range in the magnitude of immune memory.”

Alessandro Sette, Doctor of Biological Sciences an Italian immunologist in a blue sweater
Alessandro Sette, Doctor of Biological Sciences (above), an Italian immunologist, Professor at the Center for Autoimmunity and Inflammation/Center for Infectious Disease and Vaccine Research at La Jolla Institute for Immunology, and co-author of the study, told the Washington Post that people should act responsibly. “If I had COVID, I would still not throw away my masks, I would not go to rave parties … It’s like driving a car where you know you have 90% probability that the brakes work.” (Photo copyright: La Jolla Institute for Immunology.)

Previous Studies Found Little Natural Immunity Against SARS-CoV-2 Reinfection

The Scientist reported that several widely publicized previous studies raised concerns that immunity from natural infection was fleeting, perhaps dwindling in weeks or months. And a United Kingdom study published in Nature Microbiology found that COVID-19 generated “only a transient neutralizing antibody response that rapidly wanes” in patients who exhibited milder infection.

Daniel M. Davis, PhD, Professor of Immunology at the University of Manchester, says more research is needed before scientists can know for certain how long COVID-19 immunity lasts after natural infection.

“Overall, these results are interesting and provocative, but more research is needed, following large numbers of people over time. Only then, will we clearly know how many people produce antibodies when infected with coronavirus, and for how long,” Davis told Newsweek.

While additional peer-reviewed studies on the body’s immune response to COVID-19 will be needed, this latest study from the La Jolla Institute for Immunity may help guide clinical laboratories and in vitro diagnostic companies that are developing serological antibody tests for COVID-19 and lead to more definitive answers as to how long antibodies confer protective immunity.

—Andrea Downing Peck

Related Information:

Immunological Memory to SARS-CoV-2 Assessed for up to 8 Months After Infection

Protective Immunity Against SARS-Cov-2 Could Last Eight Months or More

Covid-19 Immunity Likely Lasts for Years

Longitudinal Observation and Decline of Neutralizing Antibody Responses in the Three Months Following SARS-CoV-2 Infection in Humans

Studies Report Rapid Loss of COVID-19 Antibodies

10 Percent of Wuhan Study Patients Lose Coronavirus Antibodies Within Weeks