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.
“Antibodies against nucleocapsid will be present only in recovered individuals and not vaccinated,” Dr. Asiya Zaidi, a research fellow at the Associazione Naso Sano and one of the authors, told The Epoch Times in an email.
That means even the people who got vaccinated received protection from natural immunity.
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,” Zaidi said.
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.
