LurkerJ said:
New data from Israel and the United Kingdom painted a confusing and contradictory picture on Thursday as to the effectiveness of Pfizer’s COVID-19 vaccine in fighting off the Delta variant of the coronavirus. New Health Ministry statistics indicated that, on average, the Pfizer shot — the vaccine given to nearly all Israelis — is now just 39% effective against infection, while being only 41% effective in preventing symptomatic COVID. Previously, the Pfizer-BioNTech vaccine was well over 90% effective against infection. Meanwhile, a new UK study published this week in The New England Journal of Medicine found the same vaccine to be 88% effective in preventing symptomatic COVID — more than twice the rate found in the Israeli data. Israel’s research agreed, at least, that the shot was highly effective in avoiding serious illness, at 91.4% effectiveness. Some analysts have warned that the figures on vaccine effectiveness are prone to major inaccuracies because of a range of factors, including questions over whether there is accurate data on infection levels among the non-vaccinated, which is vital for such stats. Davidovitch added: “It’s still excellent, very good in preventing severe cases and death, but less so in preventing transmission. And this is why we can’t rely on vaccinations alone, but also need Green Passes, testing, masks, and the like.” |
I think part of the problem in Israel could stem from control group issues. But the high efficacy against serious illness indicates that the unvaccinated seropositive aren't mostly to blame for it. Neither are waning IgG antibody levels, which are still higher at 6-9 months for Pfizer than AZ's peak.
I've seen the following hypothesis: you need a decent level of IgA antibodies to have sterilizing immunity against most diseases. Vaccines generate no IgA antibodies whatsoever, but compensate by B-cells rapidly moving to the upper respiratory tract and shedding a lot of IgG antibodies in case you come into contact with the virus. It could be that with time their levels rapidly wane in the blood.
Edit - I was mistaken about the first point: it's possible to have an artificially low eff. against symptomatic disease and high against severe disease if one is being calculated as odds ratio instead of risk reduction compared to overall cases.
Last edited by haxxiy - on 23 July 2021
