Today Moderna announced that its COVID-19 vaccine is 94.5 percent effective. As with the Pfizer announcement earlier, it’s hard to tell exactly what that means. But, based on the article cited just above, it appears to be 95% effective in preventing disease severe enough that the infected person sought medical treatment and was tested and found to have COVID-19.
This is based on a total of five COVID-19 cases diagnosed among persons vaccinated, versus 90 among the placebo (non-vaccinated) group in their clinical trial.
Up to now, no information suggested that the Moderna vaccine would be this effective. And, certainly, their lack of track record (at ever having produced a successful vaccine) did not bode well for success. Accordingly, I had assumed that Moderna’s COVID-19 vaccine would be just as (un) successful as all their prior attempts at making a vaccine.
I was wrong.
That said, I am still puzzling over an event that occurred two months ago.
Two months ago, we got news that (some) vaccine sponsored by the US had just 70% immunogenicity. See Post #815, dated September 16, 2020. That is, just 70% of persons treated with the vaccine produced the appropriate antibodies against COVID-19. That would have set an upper limit on effectiveness of no more than 70%, and set a likely effectiveness of (perhaps) 55%.
This was the episode in which the director of the CDC talked, on camera, about masks providing better protection against COVID-19 than a vaccine. That was when he announced the 70% immunogenicity of (whatever) vaccine he was referring to.
The common assumption was that this was the Moderna vaccine. I.e., both the Johnson and Johnson and Pfizer vaccines had published their immunogenicity data months earlier, per Post #827, and showed virtually 100% immunogenicity.)
Now that I look a little harder, I have no clue what the CDC director could possibly have been talking about. By the date of that news conference, Moderna had also published its immungenicity data and showed high immunogenicity of its vaccine.
In any event, these results are not coming from the manufacturers, but from the Federal panel chosen to oversee the clinical trials. So, absent some wacky conspiracy theory, we have to take them at face value. Whatever-it-was that the CDC director was discussing two months ago is now just an odd and unexplained footnote. As was the fairly common expectation among infectious disease professionals that the COVID-19 vaccines would be far less effective than the Pfizer and Moderna vaccines appear to be.
As a final footnote, you cannot compare the effectiveness of these vaccines, as stated, with the effectiveness of the seasonal flu vaccine. The COVID-19 research is using a different measure than the flu vaccine research. For flu, they count as failures all persons with any evidence of infection with flu at any point, based on antibodies found in their blood. The “ineffective” flu cases include a significant fraction of individuals who were never sick with flu, and were only known after-the-fact to have been infected with flu, based on a blood test. By contrast, the COVID-19 results appears to be based on counts of individuals who had symptoms severe enough to prompt them to seek medical treatment, and then to get tested for COVID-19. Asymptomatic infections are never counted. Because of that, the effectiveness measures for the COVID-19 vaccines will appear higher than the effectiveness numbers for the seasonal flu vaccine.