Since the emergence of the coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in December 2019, researchers have scrambled to determine if those who have recovered have lasting immunity against the virus.
Previously, scientists showed that the body’s immune system produces antibodies against SARS-CoV-2 for an average of three months.
Immunity against SARS-CoV-2
Now, a team of scientists at the Reykjavik-based deCODe Genetics, a subsidiary of the U.S. biotech company Amgen, and several universities and hospitals in Iceland, says that the antibodies developed to fight SARS-CoV-2 last for at least four months and do not fade quickly as previously thought.
In the study, published in the New England Journal of Medicine (NEJM), the researchers tested more than 30,000 people in Iceland, in one of the most extensive works yet on antibodies against the novel coronavirus and the immune system’s response to the virus over time.
The study findings will help in the development of candidate vaccines, showing that if a vaccine can trigger the production of long-lasting antibodies, it provides hope in containing the spread of the virus.
To arrive at the study findings, the research team measured the antibodies in serum samples from 30,576 people in Iceland, using six assays. They determined that the most appropriate measure of seropositivity was a positive result with both Ig assays.
From there, they examined 2,102 samples collected from 1,237 people up to four months after being diagnosed with COVID-19. The team measured antibodies in 4,222 quarantined individuals who were exposed to SARS-CoV-2 and in 23,4523 people who did not know if they had been exposed.
Of the 1,797 people who have recovered from SARS-CoV-2, 1,107 of the 1,215 who had been tested were seropositive. The team also found that antiviral antibody titers increased by two months after being diagnosed and remained constant for the remainder of the study period.
From the people who were quarantined, 2.3 percent were seropositive, and for those who have unknown exposure, 0.3 percent were positive. The researchers estimated that about 0.9 percent of people in Iceland were exposed and infected with SARS-CoV-2, and the infection was fatal in 0.3 percent.
Further, the team estimated that about 56 percent of all infections with SARS-CoV-2 in Iceland had been diagnosed with the quantitative polymerase chain reaction (qPCR), 30 percent happened in persons outside quarantine and not tested with qPCR, while 14 percent happened in quarantined persons who had not received a positive result.
“Our results indicate that antiviral antibodies against SARS-CoV-2 did not decline within 4 months after diagnosis. We estimate that the risk of death from infection was 0.3% and that 44% of persons infected with SARS-CoV-2 in Iceland were not diagnosed by qPCR,” the researchers concluded in the study.
The researchers also noted that not everyone developed antibodies after being infected, suggesting that some people may have weaker immune systems to the virus. However, it is also possible that these people had a false negative result and were not sick with COVID-19 in the first place.
Among those who have recovered, the antibody levels were higher in older people and those who were more severely affected by the virus. Also, women, who tend to not fall as sick as men to the virus, had lower antibody levels.
In smokers they had lower antibody levels against the novel coronavirus. This may be explained because smoking increases the likelihood of severe COVID-19 illness among young adults. Further, smoking may increase the expression of ACE2, the gateway that the virus uses to enter and infect cells.
The team emphasized the importance of the relationship between the humoral immune response to SARS-CoV-2 infection and protection against reinfection by this virus. Based on the results, the team has found that Iceland is at a high risk of a second wave of infection if there is no available vaccine against SARS-CoV-2.
The coronavirus pandemic has now affected 188 countries and territories. The global case toll has topped 25.75 million cases, with more than 857,000 deaths.