Thread by @ChrisMasterjohn

Flu vaccines are not tested according to their ability to make you not get sick or get less sick.

They are tested for their ability to generate a negative PCR test among people who are equally sick.

Don’t ask me, ask @mlipsitch who reviewed the topic here:

ncbi.nlm.nih.gov/pmc/articles/P…

@mlipsitch 90% of all vaccine efficacy studies since 2011 have been test-negative case control studies, first pioneered in 1980 for the pneumococcal vaccine.

@mlipsitch Vaccine trials are based on this approach. They should be called test-negative RCTs.

@mlipsitch In the test-negative design EVERYONE INCLUDES is a “clinical case.”

This means everyone included is equally sick.

A PCR test is then used to differentiate those who test positive or negative for the pathogen of interest.

This means it is NOT POSSIBLE for these studies to show ANY reduction in the severity or incidence of illness.

Rather, the vaccine generates a NEGATIVE TEST among fully sick people.

See table 2 in the above paper.

143 flu studies showed efficacy as a negative test among people with influenza-like illness.

In 47 flu studies, everyone included had acute respiratory illness.

In 9 studies everyone had “severe acute respiratory illness.”

In 4 everyone was equally sick with pneumonia.

In 4, everyone equally had febrile respiratory illness.

In 40, the inclusion criteria was a mix of the above.

In 6, everyone was equally sick with “unspecified” illnesses.

So no, the flu vaccine is not 40-60% effective at making you not get sick.

It is 40-60% effective at making you test negative for the flu strain that was targeted that season after you are just as sick with a respiratory illness.