By Eyal Shahar at Brownstone dot org.

Everyone is familiar with the results of the Pfizer Covid vaccine trial, published back in December 2020. The endpoint was "confirmed Covid," defined as at least one symptom coupled with a positive PCR test.

Not very many know, however, that the famous trial had another key endpoint - asymptomatic infection. It appears in a long document titled "Final Full Clinical Study Report."

Between one-third and one-half of SARS-CoV-2 infections were asymptomatic, and asymptomatic transmission was believed to have played a key role in the pandemic (it didn't). That was the official explanation for imposing lockdowns (though not necessarily the true one). And that's why asymptomatic infection was deemed an important endpoint in the trial.

The results are found in several places in the Pfizer document. One representative table is shown below. We find similar results in other tables.

The number of people was almost identical in the two arms, but the time at risk was only about half for placebo recipients because most of them eventually received the vaccine (crossover after unblinding). Since the number of asymptomatic infections was similar (644 versus 625), the rate ratio is about 0.5, which means 50% effectiveness. Exact computation below:

Not as good as 90% to 95% effectiveness against symptomatic infection - if you believe in miracles - but still, the risk was cut by half.

Was it?

We'll find out shortly.

A footnote explains who was included in the analysis:

Negative N-binding antibody result at visit 1

Negative PCR at visits 1 and 2

Negative PCR at any other time, when measured for suspected symptoms

A case was identified by detecting N-binding antibodies sometime after the second injection.

The N-binding antibody blood test is not as widely known as the PCR test. This test identifies antibodies that target the nucleocapsid (N) protein. They are markers of past infection.

For reasons that are not completely understood, vaccination is associated with a lower anti-N-antibody response to a subsequent infection, and the test misses many more infections in the vaccinated than in the unvaccinated. In technical terms, the sensitivity of the test is lower in the former. This observation was reported by three groups.

Allen et al. found that anti-N antibodies were detected in only 26% of cases of post-vaccination infection (6/23), which was confirmed by PCR and anti-S (spike) antibodies. The frequency was 82% in all documented previous infections (663/812). Evidently, the test underperformed in the vaccinated, and the correction factor is 3.1 (82/26). It was the Pfizer vaccine.

Follman et al. examined the same issue in recipients of the Moderna vaccine. Among participants with PCR-confirmed Covid during the blinded phase of the trial, seroconversion to anti-N antibodies was found in 40% of vaccine recipients (21/52) versus 93% of placebo recipients (605/648). Again, the test underperformed in the vaccinated, and the correction factor is 2.3 (93/40).

Dhakal et al. corroborated the findings in a series of graphs, showing persistently lower anti-N antibody response over time in post-vaccination infection. They did not provide similar percentages.

A valid comparison of the two arms of the Pfizer trial requires correcting the number of asymptomatic infections in the vaccine arm to account for underdetection by the test. It was a lot more than 644 cases. Based on the studies I cited, we should multiply that count by 2 to 3.

If we double the number (a correction factor of 2), the true effectiveness was about zero. If we multiply by 2.5, we are entering the range of negative effectiveness.

The Pfizer vaccine was useless or worse against asymptomatic infection.

My search of PubMed did not find any articles on the mRNA vaccine and asymptomatic infection in the Pfizer trial. I wonder why. Were they reluctant to publicize 50% effectiveness, or were they worried that a post like mine might show up as a letter to th...