Two new studies provide encouraging evidence that Covid-19 offers some protection against future infections. The researchers found that people who made antibodies to the coronavirus were much less likely to test positive again for up to six months and possibly longer.
The results are a good sign of vaccines, which stimulate the immune system to make antibodies – substances that attach to a virus and help clear it.
The researchers found that people with antibodies to natural infections “have a much lower risk … on the order of the same protection you would get from an effective vaccine” of getting the virus again, said Dr. Ned Sharpless, director of the US 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 coronavirus work because of the pandemic.
Both studies used two types of tests. One is a blood test for antibodies, which can go on for many months after infection. The other type of test uses nasal or other samples to detect the virus itself or parts of it, which suggests a current or recent infection.
A study published Wednesday by the New England Journal of Medicine included more than 12,500 health workers at Oxford University hospitals in the UK. Of the 1,265 who initially had coronavirus antibodies, only two had positive results on tests to detect active infection in the following six months and developed no symptoms.
This is in contrast to the 11,364 workers who initially had no antibodies; 223 of them tested positive for infections in the following six months.
The National Cancer Institute study enrolled more than 3 million people who had antibody tests from two private laboratories in the United States. Only 0.3% of those who initially had antibodies later tested positive for the coronavirus, compared to 3% of those who lacked such antibodies.
“It’s very gratifying” to see that the Oxford researchers saw the same risk reduction – ten times less likely to have a second infection if antibodies are present, Sharpless said.
His institute’s report was posted on a website where scientists share research and is currently being reviewed in a major medical journal.
The results are “no surprise … but it’s really comforting because it tells 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 is also study played no role.
Antibodies themselves may not offer protection, they could just be a sign that other parts of the immune system, such as T cells, are able to fight off new exposures to the virus, he said.
“We don’t know how long this immunity will last,” added Wolf. Cases where people have received Covid-19 more than once have been confirmed. “People must continue to protect themselves and others by preventing re-infection.”
(This story was posted by a wire agency feed with no changes to the text.)
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