Salivary IgG to SARS-CoV-2 after mild COVID-19

A team of researchers based in Stockholm, Sweden, has demonstrated that individuals exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have antibodies for the disease up to nine months after acquiring the disease, even if they displayed only mild symptoms.

Study: Persisting Salivary IgG against SARS-CoV-2 at 9 Months After Mild COVID-19: A Complementary Approach to Population Surveys

Concerns of COVID reinfection

Symptoms of SARS-CoV-2, the underlying agent for coronavirus disease 2019 (COVID-19), vary massively amongst populations of different age groups and health conditions. Most notably, people over the age of 60, and those with underlying health conditions – predominantly lung and autoimmune – tend to suffer worse than younger individuals. Older age groups especially suffer more fatalities and more serious afflictions.

There has been concern that antibody protection from the virus may only last for few months after the infection has passed, meaning that individuals can be reinfected with the disease, allowing the pandemic another avenue to continue spreading and increasing the risk of severe infection or fatality.

Professor Margaret Sällberg Chen and colleagues now present firm evidence to suggest that COVID-19 immunity persists in the saliva of previously infected individuals for nine months after infection. Salivatory antibodies are one of the first defense measures against COVID-19, as the oral and nasal cavity is one of the principal gateways for the virus to enter the human body.

A pre-print version of the research paper is available to read in full on the medRxiv*server.

What did the researchers do?

Sällberg Chen and colleagues used a multiplex bead-based array platform to investigate antibodies specific to SARS-CoV-2. They recruited saliva samples from convalescent patients from 1-9 months after symptomatic infection from SARS-CoV-2, undiagnosed self-reported individuals, and pre-pandemic reference samples.

What did the study find?

The researchers noted four key findings. Previous studies had found evidence that those who suffer milder COVID symptoms lost antibody immunological memory quite quickly. This data finds otherwise. Firstly, and most importantly, SARS-CoV-2 specific salivary antibodies persist in the bloodstream for up to 9 months post-infection, even in mildly affected individuals.

Additionally, after infection, salivary antibodies can recognize viral spikes and nucleocapsid proteins of SARS-CoV-2. They found that the body’s produced these antibodies in undiagnosed individuals who reported COVID disease-like symptoms. Finally, that saliva Immunoglobulin G (IgG) is a stable protein that can tolerate both biosafety require temperature and detergent pre-treatment.

What do the authors suggest?

“All together representing a non-invasive approach suitable for population-based immunity surveys,” says Sällberg Chen and co-authors. “Ideally, if the latter is sampled at home and mailed to the  lab, it can help protect vulnerable persons at risk for severe COVID-19 by sparing the need to visit the laboratory units for blood drawls.”

The authors suggest that self-submitted salivary samples are a far less invasive and safer alternative to submitting immunity surveys, rather than subjecting potentially at-risk peoples to blood tests in laboratories.

Their data also found that saliva samples can safely be inactivated with heat treatments or a commonly used detergent in laboratories. Such treatment causes little to no variation on assay performance.

The authors conclude, “despite waning immunity concerns, the present study shows how our multiplex bead-based immunoassays can detect antibodies against SARS-CoV-2 in saliva collected at 9 months after infection in the majority of mildly symptomatic persons.”

Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Michael Burgess

Michael graduated with a first-class degree in Zoology from the University of Hull, and later received a Masters degree in Palaeobiology from the University of Bristol.