Studies show that having COVID-19 can protect against reinfection

Two new studies provide encouraging evidence that having COVID-19 can offer some protection against future infections. Researchers found that people who made antibodies to coronavirus were much less likely to test positive again for up to six months and maybe longer.

The results bode well for vaccines that provoke the immune system to make antibodies – substances that bind to a virus and help eliminate it.

Researchers found that people with antibodies from natural infections were “at much lower risk … in the order of the same kind of protection you would get from an effective vaccine,” to get the virus back, said Dr. Ned Sharpless, director of the US National Cancer Institute.

“It is very, very rare” to get infected again, he said.

The institute’s study had nothing to do with cancer – many federal researchers have switched to coronavirus work due to the pandemic.

Both studies used two types of tests. One is a blood test for antibodies, which can linger for many months after infection. The second type of test uses nasal or other specimens to detect the virus itself or bits of it, suggesting current or recent infection.

A study published Wednesday by the New England Journal of Medicine involved more than 12,500 healthcare workers at Oxford University Hospitals in the UK. Among the 1,265 who had coronavirus antibodies from the start, only two had positive results on tests to detect active infection in the following six months, and no symptoms developed.

This is in contrast to the 11,364 workers who originally had no antibodies; 223 of them tested positive for infection in the approximately six months that followed.

The National Cancer Institute study involved more than 3 million people who had antibody tests from two private laboratories in the United States. Only 0.3% of those who originally had antibodies later tested positive for coronavirus compared to 3% of those who lacked such antibodies.

“It is very gratifying” to see that Oxford researchers saw the same risk reduction – 10 times less likely to have another infection if antibodies were present, Sharpless said.

His institute’s report was published on a website that researchers use to share research and is being reviewed in a major medical journal.

The results are “not a surprise … but it’s really reassuring because it tells people that immunity to the virus is common,” said Joshua Wolf, a specialist in infectious diseases at St. Louis. Jude Children’s Research Hospital in Memphis, which had no role in any of the study.

Antibodies themselves may not provide the 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 do not 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.”


The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. AP is solely responsible for all content.