If you're pinning your hopes on a Covid vaccine, here's a dose of realism | The Guardian - David Salisbury:
October 21, 2020 - "Much has been said about how the world will return to normal when a vaccine is widely available. But that really won’t be true. It is important that we are realistic about what vaccines can and can’t do.
"Vaccines protect individuals against disease and hopefully also against infection, but no vaccine is 100% effective. To know what proportion of a community would be immune after a vaccination programme is a numbers game – we must multiply the proportion of a population vaccinated by how effective the vaccine is.
"The UK currently has among the highest national coverage of flu vaccine in the world, vaccinating around 75% of the over-65s against flu every year; most countries either do worse or have no vaccination programmes for older people. It is reasonable to expect that this level of coverage could be achieved for a Covid-19 vaccine in that age group in the UK. Therefore, if the Covid-19 vaccine is 75% effective – meaning that 75% of those vaccinated become immune – then we would actually only protect 56% of that target population (75% of 75%). This would not be enough to stop the virus circulating. Almost half of our highest risk group would remain susceptible, and we won’t know who they are....
"Now let’s look at people younger than 65 in medical risk groups. In a good year, the UK vaccinates 50% of them against flu. That means just over a third of them are going to be protected (50% of 75%). Just to make matters worse, regulators such as the US Food and Drug Administration and the European Medicines Agency have said that they would accept a 50% lower level for efficacy for candidate Covid-19 vaccines. If that efficacy level is fulfilled, we have to multiply coverage by 50% efficacy, not 75%, and suddenly it all gets more concerning....
"If we want to see population protection from a Covid-19 vaccination, we are going to need high levels of protection (coverage x efficacy) across all ages – vaccinating not just the at-risk groups, as is being planned. To stop transmission, we must vaccinate anyone who can transmit infection. Anything less means that our goal is only individual protection and not the interruption of transmission. A recent announcement from the head of the UK vaccine taskforce, that the strategy will be targeted vaccination, makes it abundantly clear that the UK vaccine strategy at the moment is not to try to interrupt transmission....
"Even if countries do decide to switch from a personal-protection policy to a transmission-interruption strategy, obstacles remain. Much will depend on the successful vaccination (probably with two doses) of people who have not previously seen themselves to be at elevated risk. The challenge will be persuading the young, for example, to be vaccinated, not for their own benefit, but for the benefit of others.
"Adherence to recommendations for any Covid-19 interventions – social distancing, lockdowns, home working, cancelled holidays or vaccinations – depend on trust. If politicians are telling us that the present impositions on our lives are only going to last until we have vaccines, then the reality is that a false hope is being promulgated.... While hope and optimism are much needed in these dark times, it is important to be transparent. We need to communicate the clear message that although targeted vaccination may offer some protection, it will not simply deliver “life as we used to know it”.
• David Salisbury is a former director of immunisation at the Department of Health and associate fellow of Chatham House’s Global Health Programme
Read more: https://www.theguardian.com/commentisfree/2020/oct/21/covid-vaccine-immunisation-protection
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