TUESDAY, Oct. 13, 2020 — After a serious case of COVID-19 you may have long-lasting immunity, a new study finds.

The finding is reassuring to patients because the immune system makes antibodies in response to SARS-CoV-2, the virus that causes COVID-19, the researchers said.

“But there is a big knowledge gap in terms of how long these antibody responses last,” said researcher Dr. Richelle Charles of the division of infectious diseases at Massachusetts General Hospital in Boston.

Her team looked at more than 300 blood samples from COVID-19 patients, most of whom had severe cases. The samples were taken up to four months after symptoms appeared.

The researchers found that measuring an antibody called immunoglobulin G (IgG) was highly accurate in identifying infected patients who had symptoms for at least 14 days. The levels of antibodies remained high for four months and were linked with high levels of other protective antibodies, which didn’t decrease over time.

“That means that people are very likely protected for that period of time,” Charles said in a hospital news release. “We showed that key antibody responses to COVID-19 do persist.”

The researchers also found that COVID-19 patients had immunoglobulin A (IgA) and immunoglobulin M (IgM) responses that dropped to low levels within 2.5 months.

“We can say now that if a patient has IgA and IgM responses, they were likely infected with the virus within the last two months,” Charles said.

Knowing how long an immune response lasts can help get more accurate data about the spread of SARS-CoV-2, said study co-author Dr. Jason Harris, a pediatric infectious disease specialist at Mass General.

“Knowing how long antibody responses last is essential before we can use antibody testing to track the spread of COVID-19 and identify ‘hot spots’ of the disease,” Harris added.

The findings were published online Oct. 8 in the journal Science Immunology.

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