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curl-6 on 12 November 2020
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SvennoJ said:
curl-6 said:

A vaccine from Canada-based Medicago starts combined Phase 2/3 trials: https://www.gsk.com/en-gb/media/press-releases/medicago-and-gsk-announce-start-of-phase-23-clinical-trials-of-adjuvanted-covid-19-vaccine-candidate/

vivster said:

There are a number of factors why we're seeing very few cases of reinfection.

1. The majority of covid cases have happened very recently

2. covid survivors are more likely to take measures to prevent another infection

3. a second infection may be less likely to have strong symptoms

4. some new infections may already be reinfections but are impossible to detect as such

There would still be way more verified cases of reinfection than there have been if it didn't confer any real immunity.

Would it really?

Take Italy, they had found some 250K cases from the first wave. There are a bit over 60 million people in Italy. Chance to have been found positive from the first wave was about 0.4%.  Based on that, the chance to catch it twice is 0.0017%.

By now Italy has found another 750K cases, 0.4% or about 3,000 people could have been reported with Covid during the first wave. So yes, maybe we should have heard more about re-infections now.

Actually we did
https://www.the-scientist.com/news-opinion/more-sars-cov-2-reinfections-reported-but-still-a-rare-event-68089

In his team’s analysis of hospital records of 100,432 individuals infected with SARS-CoV-2 between March and July 2020, only 285 (0.26 percent) presented signs that they’d contracted the virus twice.

Rare, yet the first wave was not that long ago and during the first wave most of the people that were tested already had severe symptoms triggering a bigger immune response. Plus the waves aren't necessarily hitting the same area twice.

As long as the vaccines last long enough to stop the circulation we should be good.

It is still a rare event though, and we know from looking at the blood of people who've been infected that the body doesn't just retain antibodies for several months after infection but also shows Memory B and T Cells which are key components of long lasting immunity.

Not everyone will gain an immunity, but that applies to most vaccines anyway, you don't need 100% immunity within a population to achieve herd immunity.

For example, the Herd Immunity Threshold, (HIT) or the percentage of the population that needs to be immune to prevent spread, is 80-86% for Smallpox and Polio.

The HIT for COVID-19 is not yet known, but one study suggests it could be as low as 43% to 60%, so vaccinating just two thirds of the population could be sufficient to prevents its spread. https://www.sciencedaily.com/releases/2020/06/200623111329.htm

Last edited by curl-6 - on 12 November 2020