Vaccinated people in Israel are less likely to test positive for SARS-CoV-2, but a population-wide effect will take time to become clear.
As countries worldwide roll out COVID-19 vaccines, researchers are eagerly watching for early signs that they are having an impact on the pandemic. Last week, researchers in Israel reported preliminary figures suggesting that people vaccinated there were about one-third less likely to test positive for SARS-CoV-2 than people who had not received a shot. But scientists say that population-wide effects of immunization will take time to become clear.
Many factors will determine how soon scientists can detect the impact of vaccines on the pandemic. Among them are the extent of vaccine coverage, the effectiveness of shots at preventing disease and infection, and the rate of viral transmission.