1. For a case to be officially reported as reinfection, the current standard requires obtaining distinct genomic sequences of the virus for the first and second infections.

But genomic sequencing is expensive and therefore is not usually conducted for viral samples.

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2. The percentage of people who have been confirmed as infected is still very low, e.g., about 8M/330M = 2.4% in the US.

Assuming independence of the two instances of infection, the probability that someone in the US has been infected twice is 0.024 Ă— 0.024 = 0.00058.

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3. Many patients did not even get a PCR test during the initial wave. So, we have missed many cases between January 2020 and May 2020.

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4. If the infecting viral load is not too high, many reinfections tend to be milder since the acquired immune response from a first infection seems to last for a few months.

So, many reinfections are either not detected b/c asymptomatic, or not reported & tested b/c mild.

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5. Finally, this virus has been with us for only ~ 10 months. Since there is some degree of innate immunity (due to infection) which may last for a few months, not enough time has passed to allow for many reinfections.

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Why do I believe stating "reinfections are very very rare" without definitive proof is dangerous?

A. It is against the Precautionary Principle.

https://twitter.com/SafaMote/status/1300131603260334081?s=20

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B. It can encourage risky behavior by recovered patients, which might lead to their reinfection.

For example, they might decide not to wear a mask or have close contacts with other infected people, because they believe they cannot be reinfected.

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Even patients who have recovered from a prior infection might become severely sick or die if exposed to a large viral load.

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C. Reinfected patients can infect other susceptible people and fuel the chain of transmission even further.

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But until a safe, effective vaccine becomes available, I strongly recommend wearing a FACE MASK and following Japan's 3 C's rule.

13/end
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