# Immunity freedom day for the Weekend Editrix!

Tagged: COVID

As of today, the esteemed Weekend Editrix is 2 weeks past her 2nd dose of the Pfizer vaccine, and thus as fully immunized as it’s possible to be right now. At 3pm EDT, she is officially out of COVID jail! Well, more or less…

## What it (still!) means once you’re fully vaccinated

Recall that a vaccine efficacy of 95% means that we now have 5% of the probability/unit time of getting COVID-19 as an unvaccinated person in similar exposure circumstances:

$\mbox{efficacy} = 100.0 * \left( 1 - \frac{\Pr(\mbox{infection} | \mbox{vax})}{\Pr(\mbox{infection} | \mbox{non-vax})} \right)$

But… the new variants (especially the British, Brazilian, and South African) are apparently much more contagious. So even if the vaccine is equally efficacious on them, our risk would still be 5% of a larger number. And it appears the vaccines still have efficacy, but it might be lowered. (Though the efficacy at preventing hospitalization & death might still be impressively high.)

## Herd immunity

So the risk isn’t really removed until we reach herd immunity. And, as we’ve seen, there are people diligently working to make sure that cannot possibly be attained.

Also, the virus isn’t exactly sitting still. With each variant, we’re seeing mutations in the receptor binding doman (RBD) that increase affinity to human ACE2. This increases the $R_0$, so ability of the virus to spread goes up. The fraction of the population required to be vaccinated or otherwise immune also goes up:

$p \geq 1 - \frac{1}{R_0}$

Given how we’re struggling to get people to overcome superstitious fear of vaccines already, a higher $R_0$ just raises the bar even higher. Personally, I’m putting it at about 60% probability there will be booster shots required for the variants either in the fall or early next year (2021-Q3 to 2022-Q1, if you want to hold me to it and check).

So we still haven’t booked tickets to my favorite Club Med in the Bahamas. It’s closed until December 2020 anyway. Maybe then?

In the meantime, the Weekend Editrix’s mother in Japan has gotten her first dose of Pfizer. So I foresee a trip to Japan in the summer (at least for the Weekend Editrix, given exhorbitant air travel prices right now!).

## Notes & References

1: Nope, no time for notes today. Out makin’ antibodies & teachin’ stuff to memory B cells.

Written Wed 2021-May-05