Vaccine “efficacy” refers to how well a vaccine prevents illness in the controlled setting of clinical trials. Outside the laboratory, researchers continue to monitor and study vaccine “effectiveness,” which measures how well the vaccine works in less predictable real world environments. The efficacy and effectiveness of the COVID-19 vaccines are impressive, with strong evidence that they protect against infection and prevent serious illness and death from the virus.
‘Breakthrough’ COVID cases are causing confusion. Here’s what you need to know (PBS)
Reports of athletes, lawmakers and others getting the coronavirus despite vaccination may sound alarming but top health experts point to overwhelming evidence that the shots are doing exactly what they are supposed to: dramatically reducing severe illness and death. The best indicator: U.S. hospitalizations and deaths are nearly all among the unvaccinated.
Who Had COVID-19 Vaccine Breakthrough Infections? (New York Times)
Compared with the unvaccinated, fully vaccinated people overall had a much lower chance of testing positive for the virus or dying from it, even through the summer’s Delta surge and the relaxation of pandemic restrictions in many parts of the country. But the data indicates that immunity against infection may be slowly waning for vaccinated people, even as the vaccines continue to be strongly protective against severe illness and death.
Why COVID-19 Vaccines Offer Better Protection Than Infection (Johns Hopkins)
Vaccination offers longer, stronger immunity, says virologist Sabra Klein. Virologist Sabra Klein, PhD ‘98, MS, MA, says an immense amount of data collected in a short time have made clear the safety and effectiveness of vaccines and the limited immunity that comes from being infected with the SARS-CoV-2 virus. In the following Q&A, the Molecular Microbiology and Immunology professor explains the nitty gritty of vaccines, coronavirus infections, and how to best protect yourself.
What is the difference between efficacy and effectiveness? (GAVI)
Efficacy is the degree to which a vaccine prevents disease, and possibly also transmission, under ideal and controlled circumstances – comparing a vaccinated group with a placebo group. Effectiveness meanwhile refers to how well it performs in the real world. Although a vaccine that has high efficacy – such as Moderna’s COVID-19 vaccine with 94.5% efficacy and Pfizer’s with 90% efficacy – would be expected to be highly effective in the real world, it is unlikely to translate into the same effectiveness in practice.
COVID-19 vaccines: What does 95% efficacy actually mean? (Live Science)
One common misunderstanding is that 95% efficacy means that in the Pfizer clinical trial, 5% of vaccinated people got COVID. But that’s not true; the actual percentage of vaccinated people in the Pfizer (and Moderna) trials who got COVID-19 was about a hundred times less than that: 0.04%. What the 95% actually means is that vaccinated people had a 95% lower risk of getting COVID-19 compared with the control group participants, who weren’t vaccinated. In other words, vaccinated people in the Pfizer clinical trial were 20 times less likely than the control group to get COVID-19.