Two new studies provide encouraging evidence that possession of COVID-19 may provide some protection against future infections. The researchers found that people who developed antibodies to the coronavirus were much less likely to be positive for the test again for up to six months, and perhaps longer.
The results suggest vaccines that provoke the immune system to make antibodies – substances that bind to the virus and help remove it.
The researchers found that people with antibodies to natural infections were “at a much lower risk … because of the same kind of protection you would get from an effective vaccine,” to re-infect the virus, said Dr. Ned Sharpless, director of the U.S. National Cancer Institute.
“It’s very, very rare” to get infected again, he said.
The institute’s study had nothing to do with cancer – many federal researchers switched to working on the coronavirus because of the pandemic.
Both studies used two types of tests. One is a blood test for antibodies, which can take many months after infection. The second type of test uses nasal or other samples to detect the virus itself or its fragments, indicating a current or recent infection.
The study, published Wednesday in the New England Journal of Medicine, involved more than 12,500 health workers at Oxford University Hospitals in the UK. Of the 1,265 who initially had antibodies to the coronavirus, only two tested positive for active infection in the next six months, and none developed symptoms.
This is in contrast to the 11,364 workers who initially had no antibodies; 223 of them had a positive infection test in the approximately six months that followed.
The National Cancer Institute study involved more than 3 million people who tested antibodies from two private laboratories in the United States. Only 0.3% of those who initially had antibodies later tested positive for coronavirus, compared with 3% of those who did not lack such antibodies.
“It is very gratifying to see that researchers from Oxford have noticed the same risk reduction – 10 times less likely to have another infection if antibodies are present,” Sharpless said.
The report of his institute is published on a website used by scientists to share research and is under review in a major medical journal.
The findings “are no surprise … 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. John’s Children’s Research Hospital. Jude in Memphis who had no role in any of the studies.
The antibodies themselves may not provide protection, they may just be a sign that other parts of the immune system, such as T cells, are capable of fighting any new exposure to the virus, he said.
“We don’t know how long-lasting this immunity is,” Wolf added. The cases of people who have repeatedly received COVID-19 have been confirmed, so “people still need to protect themselves and others by preventing re-infection.”
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