BBC Future – There’s no evidence that any of the current Covid-19 vaccines can completely stop people from being infected – and this has implications for our prospects of achieving herd immunity – “…In fact, most vaccines don’t fully protect against infection, even if they can block symptoms from appearing. As a result, vaccinated people can unknowingly carry and spread pathogens. Occasionally, they can even start epidemics.  “Effective” or “sterilising” immunity – There are two main types of immunity you can achieve with vaccines. One is so-called “effective” immunity, which can prevent a pathogen from causing serious disease, but can’t stop it from entering the body or making more copies of itself. The other is “sterilising immunity”, which can thwart infections entirely, and even prevent asymptomatic cases. The latter is the aspiration of all vaccine research, but surprisingly rarely achieved…”

However, most scientists aren’t expecting to eliminate the virus entirely. For the moment, the goal is to reduce its transmission as much as possible. “Even if you vaccinate, you’ve still got a fairly large number of susceptible people there,” says Head [Michael Head, a senior research fellow in global health at the University of Southampton]. “So, we will still see outbreaks happen. I think they would be fairly localised, but they would still cause concern and cause a burden of disease”…