This does not happen with the injected vaccine, which contains a form of the virus that is essentially dead and unable to replicate at all. That’s why many countries have switched to injected polio vaccines—the UK moved away from oral polio vaccination in 2004, for example. The injected vaccine is delivered in four or five doses, the first at two months of age.
How did it get here?
So why is the virus in London’s wastewater? The transmission chain probably started with a child—someone who had recently been vaccinated with the oral vaccine in another country, says Stonehouse. “That child may be absolutely fine, and may have stopped producing vaccine-derived polio by now,” she says. “But they may have passed it on to somebody else, who has passed it on to somebody else.” The virus appears to have spread through a small, but unknown, number of people in London.
I say London because that’s where the virus has been spotted. Sewage is routinely screened for a range of viruses at a couple of sites there and one in Scotland, says Stonehouse. But many virologists think the virus could be spreading more widely in the UK and beyond—it’s just that we haven’t looked.
Why now? Stonehouse puts it down to “bad luck.” It’s possible that this kind of spread has happened before and we just didn’t notice. That’s no reason to be blasé, though. “The virus spreads so easily that any indication of transmission is really worrying,” she says.
Just how worried should we be? Adults can develop severe disease, but it’s rare, and they should still be protected by any vaccinations they received in childhood. I’m feeling grateful for the vaccine-dosed sugar lump I was fed when I was a child.
It’s children under five who are at greatest risk of polio and its complications, so it’s important to make sure children are up to date with their routine vaccinations. My daughter should be protected already—she’s already had the three doses recommended for a child her age.
Children are more likely to become infected with and spread the poliovirus than adults are, and they can do so even if they’ve received the injected vaccine. A statement from the UK’s Joint Committee on Vaccination and Immunization (JCVI) mentions unpublished evidence that the whooping cough vaccine given to pregnant women can lower their babies’ immune response to their first vaccinations, suggesting that those vaccines might not be as protective in early life. That is partly why even vaccinated children like mine are being offered the vaccine now. And because the vaccine is so safe, “even if you’re fully covered, it won’t hurt to get another one,” says Stonehouse.
Polio can’t be cured, but it can be prevented. Which is why I packed my daughter, along with toddler-friendly cookies and a ready-loaded YouTube Cocomelon video on my phone, off to our local doctor on a sunny Thursday afternoon.
My eldest daughter has not been invited for a booster dose—vaccines aren’t being offered to children who have received their preschool shot (at three years and four months) within the last year. But she’ll be eligible in a couple of months’ time. I’m hoping we won’t need one by then.