Vaccine effectiveness

Over the past two weeks, there have been quite a few studies which have shown that the vaccines work as expected. For example, see:

  • The Economist — “the Pfizer-BioNTech vaccine reduced the hospitalisation rate among inoculated Scots by 85% four weeks after their first dose; the AstraZeneca-Oxford vaccine lowered hospitalisations by 94%. (The variation between the effectiveness of the vaccines may be down to age differences among the recipients rather than the vaccines themselves.)”
  • @eran_segal showing data which showed that vaccinating young people (16-18 year olds in the general public and 19-21 year olds in the army) reduced infections: “these groups dropped >50% in cases, compared to <30% drop in 13-15 y/o and 22-24 y/o who were not vaxed”
  • @ariehkovler showing data from the Israeli Health Ministry showing 98.9% effectiveness of Pfizer of preventing hospitalization or death.
  • The New York Times: “The first studies of Britain’s mass inoculation program showed strong evidence on Monday that the coronavirus vaccines were working as intended, offering among the clearest signs yet that the vaccines slash the rate of Covid-19 hospital admissions and may be reducing transmission of the virus.”

There have also been a few studies which have shown that the mRNA vaccines reduce asymptomatic cases by about 70-90%. (The Phase 3 trials looked at how much the vaccines reduced symptomatic cases.) For example, see:

Note that these are observational studies, which are not as rigorous as randomized clinical trials, but it’s not really ethical to do a randomized clinical trial by withholding a known-good vaccine. However, the studies are good studies with lots of people, and the accumulation of observational studies does give a pretty strong signal that the vaccines usually prevent asymptomatic cases.

Note that the vaccines do not prevent all asymptomatic cases, which is a strong argument for continuing to keep your mask on, keep your distance from people, etc. It is polite to not kill your friends with your asymptomatic cases.