Swedish study reveals duration of immunity after mild COVID

The world’s public health is more dire than ever as a result of the ongoing pandemic of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and its associated disease, Coronavirus Disease 2019 (COVID-19). It has become.

As a result of SARS-CoV-2 infection, antibodies are produced against a variety of viral antigens, including spikes and nucleocapsid proteins. There is evidence that antibodies to the spike S1 protein, more specifically the receptor binding domain, can neutralize the virus. Studies have shown that people with severe infections remain protected from the virus for months. However, little is known about the duration of immunity after mild infection.

A study led by Asa Bjorndal of the Swedish Public Health Service investigated the antibody response of people after mild symptoms. The survey results are Spike protein It was stable after 8 months. However, antibodies targeting the SARS-CoV-2 nucleocapsid protein declined over time.

The research team wrote:

“The well-characterized panel of serum samples presented here is valuable for diagnostic performance and quality evaluation of current and new serological assays.”

A study of “stable IgG antibody levels in patients with mild SARS-CoV-2 infection” medRxiv* server.

How they did it

Online advertising promoting the survey helped recruit participants from three counties in Sweden. Potential participants completed an online survey as a pre-screening to see if they could provide antibody-positive or negative serum samples and other demographic information. Participants did not have vaccine-induced antibodies because the vaccination campaign has not yet started in Sweden.

Patient characteristics

From October 30th to December 8th, 2020, a total of 469 participants donated serum and were included in the study. About 145 people were positive for previous COVID-19 infections. Initial sampling and follow-up showed no cases of reinfection.

Based on a follow-up visit on April 12, 2021, 28 of the 324 people who previously reported no infection were SARS-CoV-2 positive.

Approximately 85% of SARS-CoV-2 positive patients reported mild infections, with influenza-like symptoms being the most common. People who had never been infected with COVID-19 reported lung problems and believed that 17% were infected with COVID-19 in 2020.

Serum positive and antibody test

Approximately 95% of people who recovered from COVID-19 showed evidence of IgG antibodies specific for SARS-CoV-2 nucleocapsids and peplomers. The four samples, which were seronegative for IgG antibodies, showed evidence of other antibodies targeting nucleocapsids or peplomers.

Age and gender did not affect seropositive or antibody levels.

4% of self-reported non-infected individuals were found to be seropositive for antibodies targeting SARS-CoV-2. Of the 55 cases reported uninfected but suspected of being infected with COVID-19, 10 were seropositive.

People who reported moderate to severe illness had higher antibody levels to peplomer and nucleocapsids than those who reported mild symptoms.

Antibody tests showed no difference over time in IgG levels for peplomers. However, antibody levels against nucleocapsid proteins were reduced in patients diagnosed in the spring compared to when they were retested in the fall.

The results suggest that some antibodies obtained after recovery from mild infection may decrease over time. Still, researchers note that it was difficult to obtain a true negative serum sample. This is the limit of research.

One of the strengths of this study was the extensive collection of samples from the general population that showed recovery from mild COVID-19 disease, but could be sampling bias from online recruitment. Due to the non-random selection of participants, they suggest that the study results are likely to underestimate the amount of undiagnosed COVID-19 cases.

*Important Notices

medRxiv Publish preliminary scientific reports that should not be considered definitive as they are not peer-reviewed, guide clinical practice / health-related behaviors, and should not be treated as established information.