1/16 COVID Epi This Week: The Peril and Promise of Immunity

Covid continues to spread in most of the US at rates too high for effective contact tracing, safe in-person schooling, or economic recovery. Important hints published this week about immunity. https://cnn.it/2QglARk 

2/16 Getting harder to track the virus. Test volumes all over the map are … all over the map. Big increases (Alabama, Arkansas, NY, SC, TX), big decreases (Alaska, FL, LA, MS, WI), some stable (e.g. CA). Haven’t seen any good data on reasons for testing decreases.

3/16 Test positivity, the most important single indicator, falling in many states. But it is measured differently in different places. Patients vs. tests. Exclude outbreaks? Exclude screening? Exclude repeats on the same person? In any case, overall percent: from 6.9% to 6.3%.

4/16 Hospitalizations are falling, which is good news, but important to keep in perspective. Per HHS Protect, approximately 55,000 patients with Covid hospitalized, with more than 10% of beds taken with Covid patients in the south, southwest, other than New Mexico (3.8%), and CA.

5/16 Back of envelope: average hospital stay 1 week, 8,000 new hospitalizations/day. 15% of diagnosed symptomatic cases hospitalized, so about 50,000 diagnosed cases a day. Actual infections at least 2x maybe 9x that number, so 100K to 450K infections/day. That’s a huge number.

6/16 Algorithm estimate a bit higher case rate, but in the same range. https://bit.ly/3eJ51HE . Same algorithm (matching CDC estimates) calculates between 30 and 60 million people in the US have been infected since the outbreak began -- 10-20% of the population.

7/16 Covid now 3rd leading cause of death. Even at “only” half current death rate, Covid would kill
- 4x as many as from suicide, kidney disease
- 3x as many as flu and pneumonia
- 2x as many as diabetes
- More than Alzheimer’s, stroke, lung disease, injury (including opiates)

8/16 Much more to learn about immunity, and no valid reason to be confident about ANYTHING. But there are encouraging developments. Premise: infection protects some people from re-infection for some time. Vaccination, immunity passports, and some herd protection may be possible.

9/16 Intriguing, non-peer-reviewed study found that 3 (?2) people with neutralizing antibodies didn’t get infected when nearly everyone else on their fishing ship did. Infection likely results in protection of at least some people for at least some time. https://bit.ly/3gjsjV7 

10/16 Great study, worth reading. Pre-departure, 6 antibody+ people. 3 were either falsely or weakly positive, and 2 of these people became infected. Of the 3 with neutralizing antibodies, 1 had low levels of PCR positivity, reflecting either reinfection or persistent positivity.

11/16 Meaning: some infections likely lead to some protection in some people. Not enough to bet your life on, but enough to be optimistic. Now to figure out how long immunity lasts, how complete it is, and what proportion of infected people are protected. That’s the premise.

12/16 Now the peril. First, overconfidence in immunity may lead individuals and communities to let their guard down, resulting in more spread and more deaths. Second, developing immunity - from either infection or vaccination - may cause severe illness in some people.

13/16 In the fishing boat outbreak, 3 people had antibodies but not neutralizing antibodies; 2 got infected. No way to know whether these were false positive or weak positive tests, perhaps from mild prior Covid. Antibody positive does NOT mean immune. Overconfidence can kill.

14/16 Don’t count on herd immunity. Foolish academics suggest 20-30% threshold. Explain communities with 50% infection?! False dichotomy: not on/off, but degree. More people with protective antibodies, infection spreads slower. Spread is uneven, so communities remain vulnerable.

15/16 Great antibody test data from @nycHealthy 1. Testing inversely proportional to positivity. Throughout US, those most in need get least care. 2. Positivity correlates with crowding, poverty. 3. One fourth positive, although many undoubtedly false+. https://on.nyc.gov/2Q7Fs9p 

16/16 The promise. Neutralizing antibodies=immunity. Unclear for how long. Vaccination feasible, now must prove effective, safe, trusted. We can get to new normal if we stay apart & work together. Immunity passports may become reality, but immunity is not just around the corner