The coronavirus disease (COVID-19) has spread rapidly across the globe, with more than 13 million people infected. Of these, an estimated 7 million have recovered from the viral infection. However, it was unclear whether being exposed to the virus would provide long-lasting immunity. Now, a new study says that SARS-CoV-2 immunity may only last for months.
A team of researchers at King’s College London has found steep drops in recovered patients’ antibody levels against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The findings suggest that the virus could re-infect people repeatedly, just like the common cold.
Published on the preprint server medRXiv*, and not yet peer-reviewed, the study findings highlight the importance of a vaccine to protect from the infection.
Antibodies attacking SARS-CoV-2 virus, the conceptual 3D illustration for COVID-19 treatment. Image Credit: Kateryna Kon / Shutterstock
Antibodies against the novel coronavirus
The body’s immune system plays a pivotal role in providing protection against foreign invaders, including pathogens or disease-causing microorganisms. Included in the pathogens are bacteria, viruses, and parasites, among others.
The immune system contains B cells that produced antibodies or immunoglobulins, which are Y-shaped proteins in response to exposure to antigens. Just like every lock has a single key, an antibody has a single antigen key. When the key is inserted into the lock, the antibody activates, tagging, or neutralizing its target. The production of antibodies is the primary function of the humoral immune system.
Antibody testing or serology testing is performed after full recovery from COVID-19. As many countries re-open businesses and ease lockdown measures to help their economies recover, some officials believe that antibody testing is the key to a return to normalcy safely. However, this new study shows that immunity to the virus may be short-lived.
The coronavirus pandemic started in Wuhan City in China, and from there, it has spread to 188 countries and territories. Since the emergence of the virus, many countries have reported cases of re-infection.
In the study, the researchers analyzed the immune responses of 90 patients at a London Hospital and found that 60 percent of the patients developed an initially strong antibody response to infection. Only 17 percent retained that potency three months later. In fact, the antibody levels dropped as much as 23-fold in the period, and in some cases, the antibodies were undetectable.
With declining antibody levels, re-infection can occur even in those who have fully recovered from COVID-19. This means that the infection may become seasonal, with people getting it often just like common colds.
Since there seems to be a short-lived immunity against the novel coronavirus, scientists need to develop a vaccine that can effectively protect the body against infection.
“This study has important implications when considering widespread serological testing, Ab protection against re-infection with SARS-CoV-2 and the durability of vaccine protection,” the researchers wrote in the study.
In summing up, the researchers say, “In summary, using sequential samples from SARS-CoV-2 infected individuals collected up to 94 days POS, we demonstrate declining nAb titers in the majority of individuals. For those with a low nAb response, titers can return to the baseline over a relatively short period. Further studies using sequential samples from these individuals are required to determine the longevity of the nAb response fully, and studies determining the nAb threshold for protection from re-infection are needed.”
Vaccine development is underway as candidate vaccines are now being tested for their safety and efficacy. Some of the potential vaccines have entered the phase III clinical trial stage, which will determine if the vaccine can protect against the virus in a large number of people from different regions in the world.
As the current study shows that antibody levels drop over a few months after recovery, it is important that government officials and employees do not use antibody testing as a ticket to immunity.
Many countries have seen antibody testing as a way to determine the extent and magnitude of the pandemic. However, case numbers recorded in the official tally sheet may not be actual, since there are many people who do not manifest any symptoms of the infection.
The global death toll has now climbed to more than 571,000 people. The United States reports the highest number of infections, with a staggering 3.36 million confirmed cases and more than 135,000 deaths.
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.