As the coronavirus disease (COVID-19) pandemic ripples across the globe, more information emerges about neutralizing antibodies developed after being exposed to the virus. With now more than 22 million reported infections worldwide, it is essential to know if those who have recovered will develop immunity against the deadly disease.
The coronavirus disease is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is a virus akin to those that caused the earlier severe acute respiratory syndrome (SARS) outbreak in 2002-2004 and the Middle East respiratory syndrome (MERS) outbreak in 2012.
Knowing whether the virus induces an immune response and neutralizing antibodies in the human body is vital for the development of vaccines.
Now, a team of researchers at the University of Washington School of Medicine has found evidence that SARS-CoV-2 neutralizing antibodies can prevent infection in people, as they conducted a study before and after a COVID-19 outbreak on a fishing vessel.
Fishing vessel outbreak
In the study, which has not yet been peer-reviewed and appeared on medRxiv*, the researchers investigated an outbreak aboard a fishing vessel that sailed from Seattle in May. Before the departure of the ship, 122 men and women were tested to determine if they are infected with SARS-CoV-2.
Apart from this, blood samples were obtained to determine if they had antibodies against the virus, hinting at previous exposure to SARS-CoV-2. All the crew members tested negative, but three of them had antibodies indicating they had previously been infected.
A SARS-CoV-2 outbreak emerged on the fishing vessel, and the crew members who had significant levels of antibodies against the virus were protected against re-infection. Further, these crew members were later found to have antibodies that neutralized the virus and prevented infection in animals, targeting proteins the virus uses to bind and invade human cells, called the SARS-CoV-2 spike protein.
Meanwhile, three other crew members initially tested positive for antibodies against one protein, the nucleocapsid protein, of SARS-CoV-2, but subsequent analysis of their blood samples found low anti-spike antibody activity. All three became infected during the shipboard outbreak.
Colorized scanning electron micrograph of a cell (blue) heavily infected with SARS-CoV-2 virus particles (red), isolated from a patient sample. Image captured at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland. Credit: NIAID
Anti-spike antibody and neutralization assays
To further understand the outbreak in the fishing vessel, the researchers performed anti-spike antibody and neutralization assays on the blood extracted from the vessel when the crew members returned to the port.
The tests conducted showed that 104 of the 122 crew members had been exposed and infected with COVID-19 while they were in the fishing vessel. The outbreak had a high attack rate of more than 85 percent, but none of the three crew members who had antibodies were infected.
“Nonetheless, with an overall attack rate of >85%, the lack of infection in the three individuals with neutralizing antibodies was statistically significant compared to the rest of the boat’s crew. Overall, our results provide the first direct evidence anti-SARS-CoV-2 neutralizing antibodies are protective against SARS-CoV-2 infection in humans,” the researchers concluded.
A characterizing feature of SARS-CoV-2 is the protein spikes that cover its surface, which is used by the virus to attach and enter human cells. The spike of the virus contains the infectivity machinery, allowing it to enter and infect human cells. The anti-spike antibodies developed when exposed to the virus in the past, interfere with the spike protein virus protein mechanism.
The study findings highlight the importance of designing vaccines to generate similar antibodies, known as neutralizing antibodies, which can prevent infection in people. More than a hundred candidate vaccines are now underway, with six of the vaccines are in their last phases of clinical trials. Currently, the only proof that such vaccines can protect against the coronavirus comes from animal studies.
“We’re honing in on the immunological responses we need to prevent SARS-CoV-2 infection. We can’t wait to get this virus behind us,” Dr. Alex Greninger, an assistant professor of laboratory medicine and pathology at the UW School of Medicine, said.
The global case number of COVID-19 has topped 22.1 million, and more than 780,000 have succumbed to the infection. The United States is the country with the highest number of cases, with more than 5.48 million infected. Brazil and India follow with a staggering 3.40 million and 2.76 million cases, respectively.
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.