SARS-CoV-2 infection generates protective antibodies that are maintained beyond one year

Understanding the functioning and unraveling the duration of natural immunity against SARS-CoV-2 has been a major goal since the onset of the COVID-19 pandemic. Now, with the emergence of new SARS-CoV-2 variants capable of evading the immune system, it is even more necessary. Expanding on previous studies, researchers from IrsiCaixa –a center jointly promoted by the "la Caixa" Foundation and the Department of Health of the Generalitat de Catalunya–, in collaboration with the Animal Health Research Center (CReSA) of the Institute of Agrifood Research and Technology (IRTA) and the Barcelona Supercomputing Center (BSC) demonstrates in a new study that most people who have recovered from COVID-19, regardless of the severity of symptoms, have neutralizing antibodies –that is, with protective effect– beyond one year after infection. The scientific team has observed that, although in the case of hospitalized patients the production of antibodies is higher, their capacity to block new SARS-CoV-2 variants is more compromised compared to that of asymptomatic or mildly symptomatic patients, who generate fewer but more protective antibodies. However, vaccination has implied in all individuals in the study an increase in their antibody levels, reaching very similar amounts among all of them.

"This is one of the longest follow-ups done so far in people who have overcome COVID-19," explains Julià Blanco, IGTP researcher at IrsiCaixa. "Over a year, we have analyzed the protective capacity of antibodies in a group of people with very heterogeneous symptomatology and we have seen that the severity of the disease determines the magnitude and effectiveness of the immune response against SARS-CoV-2", he adds.

Different quantity and quality of antibodies depending on the severity of COVID-19

The study has been conducted in a total of 332 individuals who have undergone COVID-19, both asymptomatic and mild (~60%) and severe (~40%), and have been followed up on the neutralizing immune response for 15 months. Thus, researchers can confirm that, in most cases, antibody levels are maintained for more than one year and confer protection against SARS-CoV-2.

"What we have seen over the course of this year is that, in hospitalized patients, the amount of protective antibodies reach their maximum level few days after presenting the first symptoms and then decline sharply, until they stabilize, remaining elevated over time", says Edwards Pradenas, predoctoral researcher at IrsiCaixa and co-author of the study along with Benjamin Trinité, postdoctoral researcher at IrsiCaixa. "In the case of people who have undergone COVID-19 asymptomatically or mildly, the levels of protective antibodies, although also sustained over time, remain lower", he adds. This behaviour has been observed in infected people throughout different waves of the pandemic. In parallel, scientists have determined that, in the case of hospitalized patients, the quality of the antibodies is lower. In fact, the study shows that the protective capacity of antibodies against the Beta variant, first described in South Africa, is lost more markedly in hospitalized patients than in people who have undergone COVID-19 asymptomatically or mildly. Thus, a severe infection seems to generate more antibodies, but of poorer quality. "Having a good immune response is key, especially now with the emergence of new variants that can compromise the effectiveness of our defences. Recent data suggest that, in the absence of the vaccine, 50% of the study participants could suffer reinfection by the Beta variant of the virus, the most resistant to antibodies described so far, and this percentage would drop to 30% in the case of the original virus", says Blanco.

Achieving maximum levels of protection with vaccination

Thanks to the administration of the vaccine, the antibody levels of the people participating in the study, of different magnitude depending on the symptomatology, have reached comparable values.

"Although not all the people we have followed up have received the full course of the vaccine, we can say that, in all of them, their immune response against the virus has been boosted, demonstrating, once again, the clear benefits of vaccination", celebrates Bonaventura Clotet, director of IrsiCaixa. "However, we must continue to monitor the immunity of the population in the long term in order to know how long it lasts and whether it remains effective against new variants. Only then will we be able to design optimal prevention strategies to combat the current pandemic", he concludes.