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A study published Thursday suggested that those who have had the COVID-19 virus and produced antibodies to fight it may not enjoy a long-lasting immunity from the virus.

The study found that novel coronavirus antibodies – proteins the body makes in response to a virus – fell to undetectable levels after two or three months for 13% of people who showed symptoms and for 40% of those who did not.

The research looked at the level of antibodies in 74 people in the Wanzhou district of China – 37 who had had the virus, showed symptoms and recovered, and another 37 who tested positive for the virus but displayed no symptoms.

While the study seemed to address the question of whether a person who has recovered from the virus has lasting immunity or if they can be infected a second time, scientists caution that the level of antibodies a person has does not necessarily mean they do not have protection from a second coronavirus infection.

The study did not account for protection against the virus that is provided by other mechanisms in the body such as T-cells and memory B cells. Nor did it address the fact that even if levels of antibodies are low, they still provide some level of protection against the virus.

Dr. Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai, told The New York Times that T-cells and memory B cells are a frontline defense mechanism for the body and can spring into action upon encountering a virus they have seen before.

“If they find the virus again, they remember and start to make antibodies very, very quickly,” said Krammer.

Researchers also point out that while the study showed a decline in antibodies in COVID-19 patients, it addressed only the antibodies that attack a certain viral protein.

Other antibodies that attack the “spike” protein of COVID-19, neutralizing it, were still present, Krammer told the Times.

“The neutralizing antibody is what matters, and that tells a very different story,” Krammer said.

It is believed that for other coronaviruses such as MERS, the Middle East respiratory syndrome virus, and SARS, the severe acute respiratory syndrome, antibody immunity lasts for about a year.

Scientists had hoped that the antibodies to the COVID-19 virus would protect the body for a similar length of time.

The study did seem to find that people who do not show symptoms of COVID-19 but have contracted it – known as asymptomatic carriers — seem to mount a weaker response to the virus than those who develop symptoms.

The new study is the first to characterize the immune response in asymptomatic people.

University Of Washington Medicine Tests Blood Of Recovered COVID-19 Patients For Antibodies

SEATTLE, WA – APRIL 17: A medical laboratory scientist runs a clinical test in the Immunology lab at UW Medicine looking for antibodies against SARS-CoV-2, a virus strain that causes coronavirus disease (COVID-19) on April 17, 2020 in Seattle, Washington. The plasma she is examining came from donors who have recovered from COVID-19, a contagious respiratory illness, and may have the potential to help combat the disease in others.