With Covid-19 shots in billions of arms by now, evidence is emerging of how well they work in real-world settings. Vaccines have successfully subdued epidemics in nations where at least half of the population is fully immunized. But as more-transmissible variants spread, driving fresh outbreaks and an increase in breakthrough infections, early signs suggest that vaccines lose some potency over time. Health authorities are recommending some immunized individuals wear face-masks indoors to augment the protection, and some are turning to booster shots as well.
In general, the Covid shots are extremely good, though not perfect, at protecting against hospitalization and death. Researchers in Taiwan found that a 10% increase in vaccine coverage is associated with a 7.6% reduction in the case fatality ratio. Most vaccines also provide a very good shield against developing Covid symptoms, and some are able to provide good protection from being infected with the virus that causes Covid, SARS-CoV-2. The latter ability is important because it results in the kind of sterilizing immunity that stops the virus from spreading -- a feat that will bring the world closer to ending the pandemic via so-called herd immunity. In any case, vaccination is associated with a 40%-to-50% reduction in Covid cases among an infected person’s household contacts, and it’s anticipated that newer generation vaccines will be even better at preventing onward transmission.