• When will the UK reach herd immunity?

• Possible best case, April 2021

• Likely moderate case, June 2021

• When will US reach herd immunity? Possible July 2021.

After puzzling over why the speed of vaccination rates are seemingly lower than New York in 1947, I thought I’d look at when the UK could hit herd immunity*. I could not find any models or estimates in a google search - which I found surprising. Why has no one put an estimate out there that we could consider? Could anyone point metoone? In the spirit of thinking if you can do better, then do better, I thought I’d put a simplifying model out. My assumptions are definitely wrong but give you a sense of where we might end up.

Assumptions, useful information and data used:

• 70% of population need antibodies/protection to achieve herd immunity 

• 17% of cases are asymptomatic / not tested

• Antibodies give protection for at least 12 months, reinfection is unlikely (<5% chance)

• 3.2m UK COVID cases reported (as of 14/15 Jan)

• 2.7m vaccinations (as of 14/15 Jan)

• 33m in the UK are groups that would make 99% of deaths

• First dose gives protection

• Assumes no supply issues

• Current run rate = 274,000 vaccines a day (13 Jan)

UK Government targets:

• "Spring" for Priority Groups (33m target)

• 14m target by 15 Feb

Assuming the UK keeps up the current run rate of c. 274,000 vaccines a day, we should broadly achieve immunity by early June 2021 (assumptions below). By mid April all 33m high priority populations could be vaccinated under this run rate - so a March target is viable.  Reaching another 11m by 15 Feb (to hit 14m target), which would need 366K vaccinations a day for 30 days looks like a stretch but the UK might not miss it by far.

Assuming the UK continues to speed up vaccinations and hits 500,000 a day by the month April then herd immunity could come as early as April. Model below. This is a moderate overestimate as infection rates will come down.

Either way COVID deaths should start to fall dramatically by March, and quite possibly much early, say by early Feb if the govt can roll out these vaccines.

A faster roll out will save more lives, and normlacy comes quicker, but the UK should be able to see the light at the end of the tunnel.

Let me know major assumption mistakes or anyone else has a model out there.

Updated for a US model. This is via Youyan Gu, his site and assumptions link here. This puts the US on track for July 2021 herd immunity which looks plausible to me and aligns with my very approx. calculations, though US have to continue to improve its vaccine roll out.

Links:

* Herd Immunity = When most of a population is immune to an infectious disease, this provides indirect protection—or herd immunity (also called herd protection)—to those who are not immune to the disease.

For example, if 80% of a population is immune to a virus, four out of every five people who encounter someone with the disease won’t get sick (and won’t spread the disease any further). In this way, the spread of infectious diseases is kept under control. Depending how contagious an infection is, usually 50% to 90% of a population needs immunity to achieve herd immunity.

Asymptomatic Assumptions =17% https://www.nature.com/articles/d41586-020-03141-3

% Herd immunity assumptions = 70% https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/herd-immunity-and-coronavirus/art-20486808

Reported Data as of Jan 2021 https://ourworldindata.org/coronavirus#coronavirus-country-profiles

https://www.england.nhs.uk/statistics/statistical-work-areas/covid-19-vaccinations/

Priority Group Assessment and vaccine plan https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/951928/uk-covid-19-vaccines-delivery-plan-final.pdf