Dödligt virus från Kina orsakar panik (SARS-CoV-2, COVID-19)

Researchers looked at more than 3 million people who had an antibody test for SARS-CoV-2. SARS-CoV-2 is the virus that causes COVID-19.

They found that about 11% of people had SARS-CoV-2 antibodies. More than 88% had a negative test. And less than 1% of tests were inconclusive.

The scientists looked at who came down with COVID-19 after the test. They analyzed up to 30 days, 31–60 days, 61–90 days, and more than 90 days after.

About 3% to 4% of people with negative antibody tests got COVID-19 in each time period. But those who had antibodies were less likely to have COVID-19 as time went on. Only 0.3% of the people with antibodies had a positive COVID-19 test more than 90 days after. Those without antibodies were 10 times more likely to get the disease.

The findings suggest that people who have a positive result from an antibody test may be at lower risk for future infection with SARS-CoV-2

The cohort of 75 149 was predominantly Hispanic (49 648/75 149, 66.1%) and included slightly more females than males (39 736, 52.9%)

Conclusions
Reinfection with SARS-CoV-2 is uncommon, with suspected reinfections more likely in women, adults, immunocompromised subjects, and those previously hospitalized for coronavirus 2019 (COVID-19). This suggests a need for continued precautions and vaccination in patients with COVID-19 to prevent reinfection.

The researchers analyzed data from Denmark’s national COVID-19 testing program, which has offered free PCR testing to roughly 4 million people living in the country. Overall, they found that a very small percentage of the population — 0.65% — experienced reinfection.

For those 65 and under, getting the coronavirus once provided roughly 80% protection against reinfection. But for people 65 and older, it provided only about 47% protection against getting COVID-19 again, further highlighting how dangerous this disease can be for older adults.

A vaccine study in South Africa — where a variant is circulating that experts fear is more contagious and may make the current vaccines less effective — found new infections in 2% of people who’d previously been infected with a different variant of the coronavirus.

Cases of reinfection with COVID-19 have been reported, but remain rare​.​