Fully vaccinated Cypriots show higher antibody levels than those infected

Preliminary data from an ongoing study in Cyprus show that antibody levels following vaccination with the first and second dose against COVID-19 are at much higher levels than with people who were infected with the disease, the University of Cyprus Biobank announced on Monday.  But the study also showed that antibody levels did drop a few months after the second vaccine dose.

This data has not been included in the publication of the study but is in line with relevant observations made by other scientists studying different populations and puts credence to the view that the decision for a third booster vaccine dose was appropriate, the press release said.

"Our team stresses that vaccination is the best method of protection against COVID-19 at a personal, family and social level," the press release notes.

According to the University of Cyprus Biobank the first results of a study carried out was on the production of circulating immunoglobulin class G (IgG) antibodies against SARS-CoV-2 in individuals in Cyprus with past infection. Τhe conclusions of the study say, among other things, that IgG levels increase in the first three months post-infection and then decrease.  But they still remain detectable more than six months post-infection.

The study included individuals of the general population, with or without previous SARS-CoV-2 infection, who were invited to visit the Biobank at the Center of Excellence in Biobanking and Biomedical Research of the University of Cyprus. Serum IgG antibodies were measured using the SARS-CoV-2 IgG and the SARS-CoV-2 IgG II Quant assays of Abbott Laboratories.

Antibody responses to SARS-CoV-2 were also evaluated against participants’ demographic and clinical data. The median levels of the receptor-binding domain (RBD)-specific IgG in 969 unvaccinated individuals, who were reportedly infected between November 2020 and September 2021, were 432.1 arbitrary units (AI)/mL (interquartile range—IQR: 182.4–1147.3).

According to the study, higher antibody levels were observed in older participants, males, and those who reportedly developed symptoms or were hospitalized. The RBD-specific IgG levels peaked at three months post symptom onset and subsequently decreased up until the 6th month, with a slower decay thereafter. IgG response to the RBD of SARS-CoV-2 is bi-phasic with considerable titer variability. Levels of IgG are significantly associated with several parameters, including age, gender and severity of symptoms.

The scientists note that although much is known about the basics of SARS-CoV-2 epidemiology in Cyprus, there are still unanswered questions concerning the immune response of the Cypriot population to SARS-CoV-2.

"Understanding the development and durability of humoral immune response among residents in Cyprus is an important scientific and public health task. The aim of this work is to describe the antibody response (N-IgG and receptor-binding domain (RBD)-specific IgG) to natural SARS-CoV-2 infection among people living in Cyprus and determine parameters associated with that response", the study says.

In total, 1,898 volunteers were enrolled in the study (19 November 2020–24 September 2021) and were tested for SARS-CoV-2 IgG antibodies. Of these, 1,112 individuals (58.6%) had reportedly been infected with SARS-CoV-2 in the past, while 786 individuals (41.4%) were not aware of a previous SARS-CoV-2 infection.

The median age of the participants was 46 years old (IQR: 35–57), 1,126 (59.3%) were males, and most of them (n = 1,413, 74.5%) were residents of Nicosia, the largest district in the Republic of Cyprus. Individuals who reported a history of vaccination (40% were reportedly partly vaccinated and 36% fully vaccinated against COVID-19) were excluded from the analyses. The final dataset included 1,132 individuals, of whom 969 (85.6%) had a self-reported history of previous SARS-CoV-2 infection and 163 (14.4%) did not.

In the conclusions of the study the authors say that their work examines for the first time the antibody response to natural SARS-CoV-2 infection in the Cypriot population using both qualitative and quantitative antibody measurement methods.

"We demonstrate that IgG levels increase in the first three months post-infection and then decrease but remain detectable more than six months post-infection. Circulating IgG levels show substantial variability, partly explained by differences across convalescent individuals in terms of gender, age, development of symptomatic disease, and the necessity for hospital care. Overall, our work provides information on the immunological response to SARS-CoV-2 infection that could help inform public health measures and interventions in Cyprus", they say.