New studies are increasing assessments that immunity to COVID-19 lasts at least 6-8 months after recovery from the disease.
Research published in Science Immunology this week looked at 25 patients recovering from the disease. Although antibodies – the immune system proteins that attack viral particles – started falling into blood samples about 20 days after symptoms appeared, the memory B cells that produce antibodies continued to rise in the blood for 150 days and remained high up to the 240-day point. This signals that the subjects’ bodies were ready to fight the virus for about eight months.
Meanwhile, researchers from two other studies found that people who made antibodies to the coronavirus were far less likely to test positive again for up to six months and possibly longer.
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The results bode well for vaccines, which cause the immune system to produce antibodies.
Read: COVID-19 antibodies vanish quickly. This does not mean that mass reinfection is looming
A study published Wednesday in the New England Journal of Medicine involved more than 12,500 healthcare workers at Oxford University hospitals in the UK. Of the 1,265 who had antibodies to the coronavirus at the start, only two had positive tests to detect active infection over the next six months, and neither developed symptoms.
This contrasts with the 11,364 workers who initially did not have antibodies; 223 of them tested positive for infection in the following six months.
A third study by the National Cancer Institute involved more than 3 million people who performed antibody tests from two private laboratories in the United States. Only 0.3% of those who initially had antibodies subsequently tested positive for the coronavirus, compared with 3% of those who did not have such antibodies.
The results showed that people with antibodies to natural infections were “at much lower risk … in the order of the same kind of protection that would get from an effective vaccine,” of contracting the virus again, said Dr Ned Sharpless. , director of the National Cancer Institute of the United States.
“It’s very, very rare” to be reinfected, he said.
The institute’s study has nothing to do with cancer – many federal researchers have switched to coronavirus work due to the pandemic.
“It’s very gratifying” to see that the Oxford researchers saw the same reduction in risk – 10 times less likely to have a second infection if the antibodies were present, Sharpless said.
His institute’s report was posted on a website used by scientists to share research and is under review in a major medical journal.
The findings “are not surprising … but they are really reassuring because they tell people that immunity to the virus is common,” said Joshua Wolf, an infectious disease specialist at St. Jude Children’s Research Hospital in Memphis who does not had no role in any of the studies.
“We don’t know how long this immunity is,” Wolf added. Cases of people receiving COVID-19 more than once have been confirmed, so “people still need to protect themselves and others by preventing reinfection.”