HPV vaccine eradicates cervical cancer

There’s one other anti-cancer vaccine that’s been incredibly successful to the extent that it’s nearly wiped out a formerly common disease in a whole generation of young people. It’s the cervical cancer vaccine, which works not by targeting the cancer itself, but by preventing infection with the human papillomavirus - HPV - that causes the majority of cervical cancers to form. It’s one of the biggest success stories in vaccine and cancer medicine the world has seen. And almost twenty years ago to the day, before it was widely known about, one of the scientists who helped to make this vaccine a reality appeared on this programme to explain what would - in the years ahead - be rolled out and how it would work. Now emeritus professor of Pathology at Cambridge University Margaret Stanley is back with a recap on how this vaccine works, how effective it has turned out to be, and why the human papillomavirus causes cancer in the first place…

Margaret - It's because the virus makes different proteins and two of these proteins actually can control cells dividing and they can grow too much and they don't age. It sticks the cell in its early juvenile state and then there are accidents in the DNA and bits of the virus get incorporated into the cellular DNA. They then control what the cell does and that's the start.

Chris - Why are some of these viruses better at doing that and causing cancer than others? Because it's a big family of viruses, the papilloma viruses, and some are linked to this specifically. How is that achieved?

Margaret - You call the viruses a family. Like all families, they have white sheep and black sheep. The black sheep are those that encode proteins that have this capacity to deregulate the cell. Now these proteins are essential for the virus to make its virus DNA and, if they're made at the wrong time, that's when things happen in the cell. It's only a few of the black sheep viruses that have these proteins. It's specific to a group of viruses, even though it's a huge family.

Chris - And before the vaccines came along, what fraction of the population, if I picked a person at random from the population, would be carrying, or infected by, or have had a run in with some of these viruses capable of causing things like cervical cancer?

Margaret - Well actually 80% of us either will have had one of these viruses, are going to get one of these viruses, or have one at the time. But most of us get rid of them. We have great immune systems and the immune system gets rid of the virus. But some of us are unlucky. We're unlucky in our genes and when we get the virus we are unlucky in the age at which we get it. That's when you get a group of things that really increase your risk. It's not necessarily going to happen, but you've got a big risk of it happening.

Chris - And how has the vaccine made a difference to that process?

Margaret - It prevents the virus infecting because the virus has to stick to the outside of the target cell and get inside to start its business. Now, the vaccine causes antibodies and they bind to the surface of the virus and prevent it actually entering the cell. They prevent infection in what's called a sterilising immunity. And because you've prevented infection, you ain't got no virus there, so the sequence of events I've described doesn't happen.

Chris - If one looks at what has happened in the years since we introduced the vaccine in a number of countries, what difference has that made to cervical cancer rates?

Margaret - In the UK we vaccinate school kids, I think it's year seven, year eight. Before Covid we were getting 80 to 90% coverage. After Covid it dropped, but it's starting to come back and everybody's working hard. If you get that high coverage, then I can tell you the number of precancers caused by these viruses has virtually disappeared. In women under 30 invasive cervical cancer has virtually disappeared. It hasn't disappeared in the older women because they haven't been vaccinated, but the women under 30 have been vaccinated. If you've been vaccinated, you will not get the cancers caused by these viruses.

Chris - That's quite a turnaround, isn't it? I remember when I went to medical school, learning about cervical cancer, and more than a thousand women a year in the UK alone were losing their lives to cervical cancer. And you are saying now that if we follow the cohort of people who are about 30 and below, that number will effectively be zero?

Margaret - It will. In the UK we've actually controlled cervix cancer very well. Our screening program, despite all the things shouted about it, works well, but you have to come and participate in it for it to work. Before the vaccine, we had something like 3 to 4,000 cases of cervix cancer a year and about a thousand women died. Now, with the vaccine, we have something like 200 cases of cervix cancer and the mortality has fallen equivalently.

Chris - Really encouraging stuff. In terms of the virus itself, is there a risk that because we vaccinate against certain types of the virus, that some other rarer forms will become more prominent because they're not represented in the vaccine? Or does the vaccine end up suppressing those as well because it is a big family of viruses?

Margaret - I don't think so. This of course is something that the scientific community is taking note of and there are big, big studies all over the Nordic countries where you can follow people very easily. So far there's no evidence of what we call type replacement. The other thing is, these are DNA viruses and they're incredibly stable. In fact, they use our body's own DNA repair mechanisms to repair themselves. So these are viruses that do not mutate. So far it looks as though type replacement is not an issue to worry about.

Chris - Will the viruses disappear in the population, effectively, eventually?

Margaret - That's the idea providing we immunise enough people. The name of the game is vaccine coverage. You've got to be in it to win it. You've got to have your vaccine because then you are protected. If there's hardly any virus, you can't infect anybody: the virus has nowhere to go. It has to move to another person to make more viruses. If that other person is vaccinated, you can't infect them.