Thread by @drmusanordin

In influenza, hemagglutination inhibition (HAI) titer of 1:40 is thought to provide 50% protection from infection
This assay is used to predict Vaccine Efficacy (VE) and to assist in the annual reformulation of seasonal influenza vaccines.
 ema.europa.eu/en/documents/s…

https://twitter.com/dominicabyc/status/1416259993192439810

Neutralizing antibody levels is highly predictive of protection in COVID
This apart from T cell responses or B cell memory responses as additional potential correlates of protection.

nature.com/articles/s4159…

Analysis of the relationship bet in-vitro neutralization levels & clinical protection suggested:
Neutralization level for 50% CLINICAL protection = 20.2% of mean convalescent level (14.4–28.4%)
For 50% protection from SEVERE infection = 3% of mean convalescent level (0.7–13%)

In vitro studies have shown that neutralization titers against VOC are reduced compared with titers against wild-type virus.
eg the neutralization titer(NT) against the B.1.351 variant in vaccinated individuals is 7.6X - 9X lower compared with the early Wuhan-related UK variant.

The model can predict the difference in VE against wild-type & variant viruses from the difference in neutralization level.
The dashed line indicates equal protection against wild-type and variant strains.

It predicts that a lower NT against a VOC will have a larger effect on vaccines for which VE against the wild-type virus was lower.
eg 5X lower NT is predicted to reduce VE from 95% to 77% in a high efficacy vaccine, but from 70% to 32% for a vaccine with lower initial VE

The 3X lower NT in Sinovac (VE 50% against original strain) would reduce it’s VE much more than it would for Pfizer (VE 95%)
In the press release it did not mention the drop in VE.
Obviously for Sinovac it would be below the 50% VE threshold set by the WHO
reuters.com/world/china/ar…

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