‘Fighting the pandemic isn’t only about vaccines and drugs. It’s about understanding how viruses mutate and change inside us, and among us...
‘The major change to the immunity of all the hosts SARS-CoV-2 is likely to try to infect will be, of course, vaccination. That’s human ingenuity fighting viral expertise, but it can also exert a kind of direct adaptive pressure on the virus. History has examples of so-called leaky vaccines—those that aren’t effective enough to prevent all infections or all transmission, and allow better-adapted variants of whatever bug they’re trying to squish to live to fight another day.
‘In fact, one group of researchers has a model that suggests that could even happen with the new batch of vaccines against Covid—especially those that require two doses and seem to confer different levels of immunity depending on how far apart they’re administered, or whether someone skips the second one. Here's how: If one extreme is a population totally naive to a new virus, completely vulnerable and with no immunity, and the other extreme is a population with perfect sterilizing immunity, what happens to a population in between? If a vaccine allows infection but no transmission, the virus doesn’t have a chance to evolve.
‘But if a vaccine or vaccination strategy allows some infection and some transmission? “The ones that are the best at getting around the host’s defenses are the ones that are most likely to persist,” says Caroline Wagner, a bioengineer at McGill and one of the people working on the model. If that’s all true, a leaky vaccine or leaky vaccination strategy could actually drive antigenic drift and create even worse variants. Wagner and her colleagues acknowledge that they don’t have enough data to put bounds on their model yet, but they worry about strategies like one proposed in the UK to abandon second doses as a way of speeding the process and husbanding scarce vaccine, or the way some countries are hoarding vaccine while others go without (potentially letting the virus, and variants, circulate and evolve freely).’
Read here (Wired, Mar 1, 2021)
