Posted on 30 September 2021

​This week in the UK, isolation rules changed for those who are double jabbed and received two doses of any of the approved coronavirus vaccines in the United Kingdom. The change, set out on 16th August, also applies to anyone under the age of 18, those enrolled in coronavirus vaccine trials, or those ineligible for vaccination due to medical reasons. This change means that those who are a close contact of someone who tests positive do not need to isolate for ten days but are rather advised to take a PCR test. The foundation of coronavirus policy both globally and in the British Isles has been around isolation if in contact with a positive case, something which undoubtedly served to reduce further transmission and prevent exponential spread of the epidemic. However, with no sterilising vaccine currently in development or approved, is it now safe to do away with isolation for vaccinated individuals?

Other vaccines such as measles (MMR), are sterilising vaccines which means they prevent transmission of disease onto other individuals and protects the vaccinated individual from infection. With the current vaccines employed around the world for Covid-19, it appears the efficacy lies more with prevention of severe disease and death, as transmission is still possible. There is debate as to how much transmission still occurs, with figures ranging from 40-60% reductions reported for the Pfizer and Oxford vaccines respectively (source: GAVI). However, there have been numerous reports of breakthrough cases around the world with the surge of the Delta variant, which has tenuous evidence of vaccine escape. In the US, between January 2021 and April 2021, approximately 10,000 breakthrough cases occurred in a sample of over 50 million people with double vaccination. However, the CDC changed their counting of breakthrough infections to only those hospitalised, meaning data is sparse. The 10,000 number is almost certainly an artefact of behaviour and can be expected to be much higher, as those double vaccinated may neglect to test regularly or come forward with mild illness.

One thing is certain, and that is that coronavirus vaccines definitively and reliably protect against severe illness and death, with the efficacy percentages in the high 90s for nearly all vaccines that have been made available in the United Kingdom. Early in the year though, it was reported that many people vaccinated with just one dose were liable to illness and hospitalisation, but the number was vanishingly small for those who have both jabs. Between February and July 2021 in the UK, 12% of new coronavirus infections occurred in people who had been fully vaccinated. There are numerous factors at play here, not least individual differences in immune response, something which cannot be controlled. There is a subset of individuals who may gain little benefit from vaccination, but again this is a minority. Clearly, there is some protection from transmission, but with the ONS yesterday reporting 94% of people in the UK having protection through vaccination or infection and 30,000 cases per day, Delta seems to be gaining ground.

When vaccines and treatments are introduced, a type of selection-pressure is exerted inadvertently on the pathogen. For example, bacteria introduced to an organism who later receives small doses of antibiotic mostly perish, but some (with chance mutations) survive to be passed on. A similar analogy is fitting here for singular vaccination, or a wider implication of building vaccines based on the spike protein of the SARS-CoV-2 virus. With the Delta variant, research published today (19/08/2021) reveals that viral load may be similar in vaccinated or unvaccinated people, particularly from nose and throat swabs whereby there are limited immune functions. By exerting a pressure on the virus, new variants will emerge which can and will gain advantageous mutations to ‘divert’ around the protection we have. For example, the novel MRNA vaccines built around viral RNA which produces the spike protein are ground-breaking, but do not convey as much specific protection to other potential entry mechanisms on the viral protein. For example, a future variant may mutate to enter cells through a different mechanism, rendering our spike-protein specific vaccines much less effective. This is why future booster programmes may serve to ‘mix and match’ vaccine manufacturers, to gain more immunity than sticking with one drug.

With the Alpha coronavirus present at the beginning of this year, the epidemic was controlled through the urgent vaccination programme set out by the UK government. With open borders, less mask wearing and changes to contact rules, the Delta variant took hold and has found a niche in vaccinated and unvaccinated people. The key way to prevent future variants is to reduce transmission through prophylaxis – masks, distancing and isolation. If breakthrough cases increase or even exist at a small level (<15%), and coupled with high transmission, there remains an enormous risk of a variant which is ‘familiar’ to vaccines but can evade immunity. SAGE, the scientific group advising the government, recently designated the risk of a variant completely bypassing the vaccines as ‘certain’, with a moderate to severe impact factor. Thus, being double vaccinated and not having to isolate if you are a contact of a positive case could actually serve to set us back in the progress we have made with coronavirus.

A benefit of the increased awareness is around testing, and the government recommendation to get a test if an individual is a contact is smart. But with nuance around isolation and what you can and can’t do, a breakthrough case may neglect to get tested and still spread on the virus to vaccinated and unvaccinated people. With society looking anxiously towards the return of schools, where isolation rules have also changed, we could go into a shaky autumn with high transmission in the community which is currently the case (30k cases a day). Should a variant emerge through international travel or high community transmission which is even more effective than Delta at evading immunity, we may live to regret the policies which have hastily been put in place to facilitate the opening of society. With vaccines currently reducing transmission to around 40-60%, one variant emerging with slightly more efficacy at increasing that transmission could drop the number to 20, to 10, and ultimately, to 0%. It will remain an individual decision as to whether to isolate as a contact, but in a pandemic still roaring around the world, a conservative and safety-based approach seems necessary.

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