The protection people experience after recovering from COVID-19, known widely as natural immunity, lasts for at least 18 months, according to a recently published study.
Researchers in Italy analyzed the level of antibodies in 36 patients who were documented as contracting COVID-19 in March 2020. About half of the patients went on to get COVID-19 vaccines, but the rest remained unvaccinated. Samples from all but two were tested at timed intervals, ending in September 2021, using assays that have received clearance from the U.S. Food and Drug Administration.
“At 18 months, 97% participants tested positive for anti-NCP, hinting towards the persistence of infection-induced immunity even for the vaccinated individuals,” researchers wrote in the preprint paper, which was published on the medrxiv website.
NCP stands for nucleocapsid, a part of SARS-CoV-2. Antibodies are believed to protect people against against infection from the virus.
Researchers did find that vaccination with Pfizer-BioNTech COVID-19 vaccines gave those with prior infection a significant boost, but that the increase in protection waned relatively quickly.
“Our study findings demonstrate that while double dose vaccination boosted the IgG titers in recovered individuals 161 times, this ‘boost’ was relatively short-lived. The unvaccinated recovered individuals, in contrast, continued to show a steady decline but detectable antibody levels. We do believe that further studies are required to re-evaluate the timing and dose regimen of vaccines for an adequate immune response in recovered individuals,” Dr. Asiya Zaidi, a research fellow at the Associazione Naso Sano and one of the authors, told The Epoch Times in an email.
Limitations of the longitudinal observational study include the small number of patients.
The researchers, who fund their own research, said the limited sample size was due to a lack of funding because repeated serology tests for each patient for 18 months was expensive and because following up with all the patients and reminding them of the testing was difficult.
Its strengths include the remarkable length of time.
“This is the longest observation (March 2020-September 2021) for the presence of antibodies against SARS-CoV-2 in recovered individuals along with the impact of 2 dose-BNT162b2 vaccination on the titers,” the researchers wrote.
SARS-CoV-2, also known as the CCP (Chinese Communist Party) virus, causes COVID-19. BNT162b2 is the trade name for the Pfizer jab.
Previous studies have demonstrated the powerful effect of natural immunity against the virus, including a study published in Nature in mid-January that found that the response of memory B cells, a marker of protection against severe COVID-19, evolved in the months following infection “in a manner that is consistent with antigen persistence.”
Other markers of protection were observed in studies in 2021 to last at least over 7 months, at least 8 months, at least 10 months, at least 11 months, at least 13 months, and at least 14 months. The studies were completed before the emergence of the Omicron virus variant, which early data indicate is better at evading both natural immunity and vaccine-derived protection.