Reasons to be cautiously optimistic about vaccinations

Published 10 November 2020


Pfizer has released news that their soon to be available vaccination has 90% effectiveness. This is much higher than many expected and great news.


A vaccine delivers two significant public health benefits. Firstly it stops vulnerable people from getting ill and dying, and secondly, when enough people have had the vaccine, it helps create herd immunity and slows the spread of the virus. (Arguably there is a third benefit of reducing the adverse effects of Covid and lockdown on other health needs like cancer.)*


Vaccinating the vulnerable will be the priority. Then people who are in contact with vulnerable people (e.g. health workers). With 90% effectiveness, mortality will drop substantially and should remove the need for any more lockdowns, but masks would likely still be needed and won't rush to get back on the tube.


Creating herd immunity in the general population will then be the goal. At 90% effectiveness and assuming an R of 2.5, herd immunity can be achieved once 66% of the population is immune from vaccination or having caught the disease - this will reduce R below 1, and the virus will effectively die out. This could be lower still if people remain a bit socially distant (masks, etc.), and the effective reproduction rate is lower than 2.5. 


The size of the population that needs to be vaccinated is larger if the effectiveness is lower or effective R higher. For example, if efficacy is less than the stated 90% (e.g. 80%) and R higher (e.g. 3) then up to 83% of the population would need the vaccine (less as some will have immunity from having caught the disease already) - see chart below.

This does, of course, raise the challenge of making sure that enough people get the vaccine. Logistic challenges of immunising ~44 million people (including how people who have been vaccinated are recorded in Excel) are inevitable as are supply constraints, but do we also need to worry about people's willingness to take the vaccine? 


The results of a survey shared today from Deltapoll suggests that 23% of people are "very unlikely" to want to get vaccinated. This would be fine if the vaccine is 90% effective, but it does not leave much room for error. Of course, some of these people may have already had Covid (so have some immunity), or may eventually catch it after not getting vaccinated. 


How likely would you be to take the vaccine knowing what you know now? Please do anonymously let me know in this three-question survey: https://www.smartsurvey.co.uk/s/vaccine/.  


Attitudes to the vaccine will likely improve over time - assuming it works well and does not have nasty side effects. Until that point, the impact of the vaccine would be to reduce mortality, lessen the impact on NHS critical care beds, and slow the spread of the disease - all great things! Sadly we will not see this benefit until 2021. 


* There are of course many many other benefits to society

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