A general view of the headquarters of the Centers for Disease Control and Prevention (CDC) in Atlanta.
Tami Chappell | Reuters
A new CDC study found that some elderly people who appeared to have recovered from the coronavirus later had a second, even worse case – suggesting that asymptomatic or mild cases may not offer much protection against re-infection with Covid- 19 offer.
The study, published Thursday in the Centers for Disease Control and Prevention’s Weekly Report on Morbidity and Mortality, looked at two separate outbreaks that occurred three months apart in a qualified care facility in Kentucky. According to the study, 20 residents and five health care workers tested positive for the virus between mid-July and mid-August.
The second outbreak between late October and early December was worse: 85 residents and 43 health care workers tested positive for the virus. Among residents who tested positive during the first outbreak and were still living at the facility, five tested positive a second time more than 90 days after their first positive test.
Although Covid-19 reinfections do occur, they are generally rare.
With frequent monitoring after the initial outbreak, all five residents had at least four negative tests between outbreaks, suggesting that they may have been re-infected with the virus later. Reinfection means that a person who had Covid-19 recovered and then got it again, according to the CDC.
“The history of exposure, including when the roommate infections occurred and symptoms recurred during the second outbreak, suggests that the second positive RT-PCR results represented new infections after the patients appeared to clear the first infection,” wrote Alyson Cavanaugh , one of the researchers who led the study.
While only two of the five residents showed mild symptoms during the first outbreak, all five potentially reinfected residents showed signs of illness the second time. The two residents who reported symptoms during the first outbreak “experienced more severe symptoms during the second infectious episode, according to the study.” One resident was hospitalized and subsequently died.
According to the study’s researchers, this was “noteworthy” as it suggests the possibility that people who show mild to no symptoms from their first infections “are not generating a sufficiently robust immune response to prevent re-infection”. The results “suggest the possibility that the disease may be more severe during a second infection.”
“The results of this study highlight the importance of maintaining mitigation and public health strategies that reduce the risk of transmission, even in those with a history of COVID-19 infection,” wrote Cavanaugh.
Some limitations were noted in the study. Because the samples were not stored, the researchers were unable to perform genome sequencing, a laboratory technique that breaks down the virus’ genetic code to confirm re-infection. “There are no additional test results to prove the initial test result is really positive,” they said during the initial outbreak.
It is believed that the risk of re-infection for the general population is still low, but nursing home residents may be particularly at risk due to their coexistence and the high number of exposures, according to the study.
“Qualified care facilities should employ strategies to reduce the risk of SARS-CoV-2 transmission in all residents, including those previously diagnosed with COVID-19,” Cavanaugh wrote.