Saturday, August 15, 2020

CDC Clarifies: Recovered COVID-19 Cases Are Not Necessarily Immune To Reinfection


Yesterday a number of media outlets reported that the CDC had suggested - in guidance released earlier this month - that recovered COVID-19 cases were likely `immune' to reinfection for at least 90 days.  Typical of the reporting is this from NBC News.

CDC suggests recovered COVID-19 patients have protection for 3 months

The update lines up with previous guidance that people who have recovered don't need to be retested for 90 days.

Given recent uncertainties expressed over the amount (and duration) of post-infection immunity one might expect to acquire, this story quickly made the rounds of major media.  

The source material comes from a short passage in the CDC's `WHEN TO QUARANTINE' guidance (below, underlining mine).

Who needs to quarantine?

People who have been in close contact with someone who has COVID-19—excluding people who have had COVID-19 within the past 3 months.

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. People who develop symptoms again within 3 months of their first bout of COVID-19 may need to be tested again if there is no other cause identified for their symptoms.

Quite honestly, I wouldn't have been quick to interpret this as a tacit acknowledgment of a 90-day grace period on re-infection, but I can see how some might have come away with that impression. 

While the CDC's messaging was a little kludgy, I would assume that if they had evidence of a minimum post-infection period of immunity - they'd call a press conference - not slip it quietly into a guidance doc that took 10 days for anyone to notice. 

Late last night, the CDC clarified matters in the following media statement.

Updated Isolation Guidance Does Not Imply Immunity to COVID-19

Media Statement

For Immediate Release: Friday, August 14, 2020

Contact: Media Relations

(404) 639-3286

On August 3, 2020, CDC updated its isolation guidance based on the latest science about COVID-19 showing that people can continue to test positive for up to 3 months after diagnosis and not be infectious to others. Contrary to media reporting today, this science does not imply a person is immune to reinfection with SARS-CoV-2, the virus that causes COVID-19, in the 3 months following infection. The latest data simply suggests that retesting someone in the 3 months following initial infection is not necessary unless that person is exhibiting the symptoms of COVID-19 and the symptoms cannot be associated with another illness.

People with COVID-19 should be isolated for at least 10 days after symptom onset and until 24 hours after their fever subsides without the use of fever-reducing medications.

There have been more than 15 international and U.S.-based studies recently published looking at length of infection, duration of viral shed, asymptomatic spread and risk of spread among various patient groups. Researchers have found that the amount of live virus in the nose and throat drops significantly soon after COVID-19 symptoms develop. Additionally, the duration of infectiousness in most people with COVID-19 is no longer than 10 days after symptoms begin and no longer than 20 days in people with severe illness or those who are severely immunocompromised.

CDC will continue to closely monitor the evolving science for information that would warrant reconsideration of these recommendations.

I can attest that writing clearly and concisely about a pandemic virus that we don't completely understand - without interjecting dozens of caveats or incorporating `weasel words' like `may', `might', or `could' at every turn - is a daunting task.   

And one I'm sure that - as a blogger - I've botched more than once along the way.  

As far as post-infection (or post-vaccination) immunity to SARS-CoV-2 is concerned, the jury is still out, and I suspect ultimately, the answers will be messy, and probably won't apply across the board.  

Some people will likely mount a robust (and hopefully long-lasting) immune response, and others won't.

The limited evidence we have suggests those who have mild or moderate COVID illness are likely to develop less of an immune response. And if the COVID vaccine ends up working anything like the flu vaccine, those who need the most protection (the elderly, immunocompromised, etc.) will likely derive the least benefit. 

These are all topics we've covered repeatedly over the past few months.   Some related blogs, if you missed them, include:

Imperial College London: (REACT) SARS-CoV-2 Antibody Prevalence Study - England

China: Jingzhou City Reports COVID-19 Positive Test In A Woman 6 Months After Recovery

`Forward Looking' & `Aspirational' Vaccine Press Releases

Eurosurveillance: 2 More SARS-COV-2 Seroprevalence Studies To Ponder

Kings College: Longitudinal Evaluation & Decline of Antibody Responses in SARS-CoV-2 infection