Thread by @DrZoeHyde

(1/8) Important pre-print study (interpret carefully), estimating how long vaccination lasts.

A vaccine with an initial efficacy of 95% might drop to 58% after 250 days, but a vaccine with 70% efficacy could drop to 18%.

BUT: protection from severe disease may last much longer.

https://twitter.com/tricckylab/status/1370200371214254086

(2/8) First up, the authors found a strong association between the amount of neutralising antibodies a vaccine induces, and its efficacy.

Pfizer-BioNTech (BNT162b2), Moderna (mRNA-1273), and Novavax (NVX-CoV2373) are in the top right corner.

(3/8) Based on the limited data for mRNA vaccines available to date, the authors estimated that the half-life for vaccine-induced antibodies (65 days) was similar to those produced by infection (58 days).

(4/8) From this, they could estimate how vaccine efficacy would likely reduce over time.

At 250 days, vaccine efficacy is largely preserved for vaccines with high initial efficacy.

(5/8) The authors then estimated how long it would be until a booster would be required.

Two thresholds are shown in the graph below: time until efficacy is reduced to 70% (red), and time to 50% (blue).

(6/8) The data shown so far are for efficacy against symptomatic infection, which includes mild, moderate, and severe cases.

However, we can expect efficacy against severe disease to be much higher.

(7/8) While a vaccine with an initial efficacy of 95% may fall below 50% after 1 year (for any symptomatic infection), efficacy against severe disease may be sustained around 75% for a couple of years or more.

(8/8) A limitation of these analyses, is that they are based on neutralising antibodies only.

It is possible that other, unmeasured aspects of the immune response (i.e., B cell memory and T-cell responses) could be more long-lasting.