How covid19 vaccines are effective?

There is growing evidence that people who have received COVID-19 vaccines are less likely to become infected with the virus that causes this disease.

One studyTrusted Source, for example, showed that 95% of people who received both doses of the Pfizer-BioNTech or Oxford-AstraZeneca COVID-19 vaccine had a weaker immune response to the delta variant than to previous strains.

The Health Ministry of Israel also released a statement saying that the effectiveness of the Pfizer-BioNTech vaccine in preventing symptomatic COVID-19 fell to just 64% at 6 months post-vaccination. It noted, however, that two doses of Pfizer are still able to prevent serious illness in 93% of cases.