CDC: Still No Definitive Evidence on Coronavirus Reinfection

The US Centers for Disease Control and Prevention (CDC) has been stuck in a back and forth with media for several days after misleading reporting on immunity related to COVID-19. Contradictory optimistic and pessimistic reporting on immunity has led to very little new information reaching the public.

An update provided August 16 offers some clarity, pumping the brakes on the latest coronavirus culture war by pointing out that “currently, 6 months after the emergence of SARS-CoV-2, there have been no confirmed cases of SARS-CoV-2 reinfection.”

Over the weekend, outlets pushed conflicting narratives of antibody-based immunity lasting for 3 months, waning at 3 months, and more. Reporting largely glossed over findings published in Cell on robust T cell immunity in patients who have recovered from COVID-19, treating antibody immunity as the only potential measure.

The misunderstandings started from a simple CDC guideline.

“People who have tested positive for COVID-19 do not need to quarantine or get tested again for up to 3 months as long as they do not develop symptoms again,” initial guidelines read.

The CDC guideline does not make a categorical statement about COVID-19 immunity, or reinfection, but instead outlines testing priorities based on the emerging evidence that reinfection (at least with the currently circulating strains of SARS-CoV-2) is very rare.

Much remains to be seen about antibody and other immunity when it comes to COVID-19, hence the instruction to test again if symptoms are noticed, but the recommendation from CDC is clearly now for a symptom-based strategy. How does this square with the possible SARS-CoV-2 transmission dynamic of significant mild, pre-symptomatic, and asymptomatic infections?

“Data to date show that a person who has had and recovered from COVID-19 may have low levels of virus in their bodies for up to 3 months after diagnosis,” CDC statement authors explained.

“This means that if the person who has recovered from COVID-19 is retested within 3 months of initial infection, they may continue to have a positive test result, even though they are not spreading COVID-19.”

Citing their own internal data, CDC authors also said that “for patients with mild to moderate COVID-19, replication-competent virus has not been recovered after 10 days following symptom onset.”

For severe cases, results are surprisingly similar.

“Recovery of replication-competent virus between 10 and 20 days after symptom onset has been documented in some persons with severe COVID-19…However, in this series of patients, it was estimated that 88% and 95% of their specimens no longer yielded replication-competent virus after 10 and 15 days, respectively, following symptom onset.”

While antibody testing receives the most news coverage, it is worth noting as well that antibody testing is not the only way of measuring immunity. Evidence is accumulating that cellular immunity to SARS-CoV-2 may be another, more long term development.

While the evidence is still emerging, and T cell immunity is in some ways still as shrouded in mystery and politicking as antibody immunity, there are possible implications for improving the coronavirus response strategy.

As CDC cautions, SARS-CoV-2 reinfection should not be ruled out for future patients who appear to be presenting with it. In more seasonal viruses, the annual circulating strain is especially relevant to antibody responses.

As the pandemic continues, scientific information will continue to be refined. Reports of best or worse case scenarios, as the weekend’s antibody tussle shows, are likely to be reductionist.