Once the virus enters the home, being vaccinated helps, but it could matter less than you might think. So, say your kid gets the virus—that could still mean that your family is going to have to worry a bit about getting sick as a whole.

Both a Dutch study and a U.K. study, recently posted as preprints, came to similar conclusions: In teens and adults, vaccination lowers an infected person’s chances of spreading delta to housemates by at least 50 percent. Being vaccinated (with Pfizer) reduced the chance of catching it from a housemate by 67 percent, according to the U.K. study. Pretty good—but there’s a big caveat. Those percentages were almost halved just three months post-vaccine. Another smaller but more detailed household contact tracing study paints an even starker picture. About a quarter of all household members ended up with an infection whether or not the originally infected person was fully vaccinated. On the receiving end, vaccination reduced a household member’s risk of catching the virus from 38 percent to 25 percent, but this trend didn’t reach statistical significance.

Sure sounds like you are saying that the vaccine doesn’t really prevent spread!

No, that’s not what I am trying to say. First, all studies above find some evidence that the vaccine is protective against household spread—just not as much as we’d hoped. Second, epidemiological data show that, overall, vaccinated people have much lower rates of COVID. That is, a vaccinated person is just less likely to get the virus in the first place. So yes, if the virus gets into your house, you have a decent chance of getting infected. However, vaccination means it’s less likely the virus will ever arrive on your doorstep.