The new coronavirus has raised questions on how patients fight it and what that could mean for building immunity. A new study that looked at recovered patients offers some clues. 

Researchers have found that patients fought off the virus differently because their bodies used different strategies. They also found that the antibodies that attack the virus last only for two weeks. 

Further, these findings could inform vaccine design. We do not know a lot about how the protective immune system responds to the new coronavirus. Addressing this gap in knowledge may accelerate the development of an effective vaccine, says co-senior study author Cheng-Feng Qin of the Academy of Military Medical Sciences in Beijing, China.

"Our work has provided a basis for further analysis of protective immunity and for understanding the mechanism underlying the development of Covid-19, especially in severe cases," says co-senior study author Chen Dong of Tsinghua University. 

In this study, the Chinese researchers studied 14 recovered patients who were discharged from a hospital. Eight of the patients were recently discharged, and the remaining left the hospital two weeks earlier.

The team collected blood samples from two groups: the 14 recovered participants and six others who did not have the infection, the control group. They then analyzed blood samples to look for antibodies and compared them.

They found the two protective human cells -- B and T cells -- in the blood samples of recovered patients. "These findings suggest both B and T cells participate in immune-mediated protection against the viral infection," explains Chen.

During the beginning stages of Covid-19 infection, the B cells make an antibody named IgM. After a couple of days, the cells produce the second type called IgG.

Recovered patients had higher levels of both the antibodies when compared to the control group. The team could detect them for two weeks after discharge.

Further, five of the six recently discharged patients also had high levels of another kind of antibody known to defend human cells from an invading pathogen. These five participants also had higher levels of  T cells. These cells secrete a molecule that helps strengthen the defenses.

The researchers saw that these patients developed protective cells that had different targets. In other words, they charged against different parts of the new coronavirus.

These findings suggested that our bodies fight the infection by targeting different parts of the virus -- but they do not understand the reason behind it. 

These different parts of the virus are vulnerable to an attack, they explain. Using this information, scientists can develop vaccines that strike these parts.

The findings suggest that vaccines targeting a particular coronavirus part -- called spike protein-- could work the best. Without this protein, the virus cannot infect human cells. “Our results suggest that spike protein is a promising target for SARS-CoV-2 vaccines,” the researchers explain.

The authors acknowledge one limitation: their study was small. Data from more recovered patients can help researchers gain more insights into the topic, they add.

The study has been published in Immunity.