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Coronavirus antibody levels may decline quickly, Chinese study suggests

Researchers said they found antibodies for the coronavirus started to decrease after a couple months. But experts caution it doesn't mean all protection goes away.

A recently published Chinese study suggests that antibody levels in coronavirus patients may decline only months after a person has been infected. However, experts caution that it doesn't necessarily mean a person's immunity disappears that quickly. 

The researchers found both symptomatic and asymptomatic patients' levels of antibodies fell sharply just two to three months after an infection. 

The study comprised a relatively small sample of 74 patients in China, half of whom had tested positive for the virus but didn't show any symptoms. The research was conducted by Chongqing Medical University and published in the Nature Medicine journal on June 18.

Antibodies are proteins made in response to infections, according to the Centers for Disease Control and Prevention. In general, a positive COVID-19 antibody test means that a person has been infected at some point in the past with the virus that causes COVID-19. 

Researchers said they found that after two to three months, antibodies for COVID-19 started to decrease. The study noted this is a much shorter length of time compared to similar viruses like SARS or MERS, where antibodies last for at least a year.

The data also suggested that asymptomatic individuals had a weaker immune response to the new coronavirus infection.

However, the study is relatively small and experts stress that it didn't account for other protections against the virus that is provided by other parts of the immune system like T-cells and memory B cells. Additionally, even low levels of antibodies may offer protection, the New York Times reported

“Most people are generally not aware of T cell immunity, and so much of the conversation has focused on antibody levels,” Angela Rasmussen, a virologist at Columbia University, told the New York Times.

“The finding in this paper doesn’t mean the sky is falling,” Jin Dong-Yan, a virology professor at the University of Hong Kong, told Reuters. He added that the number of patients in this study was small. He told Reuters that some cells remember how to deal with a virus after an infection and can offer protection if another round of infection occurs. 

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Researchers added that their findings support the use of public health interventions including social distancing, hygiene, isolation of high-risk groups and widespread testing.

"The strength and duration of immunity after infection are key issues for ‘shield immunity’ and for informing decisions on how and when to ease physical distancing restrictions," researchers said.

For most people, the new coronavirus causes mild or moderate symptoms. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia and death.

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