A Speculation: Has the UK reached herd immunity and what does it mean for Australia?

What happens in the UK in the next 2-4 weeks will be very instructive for Australian Pandemic policy.

Over the last couple of months the Delta strain has wreaked havoc in the UK with COVID cases rapidly rising despite high vaccination rates. High hospitalisation rates and rising deaths have followed. Last week 5,322 people were hospitalised with COVID in the UK and on July 22nd 699 people were on ventilators as a result (source of data and following image: https://coronavirus.data.gov.uk/)

In the last few days a peculiar trend has emerged in the case numbers as can be seen in the following picture:

The number of people testing positive has sharply reversed direction. This is very unusual. The normal pattern would be an initial slowing of the growth rates, a plateau and then a fall.

I can only see two explanations for this:

1/ Firstly fewer people who are getting infected are getting tested. We are already seeing a fall off in overall testing numbers as cases were rising (see picture above) but not a sharp enough fall to match the fall in the number of positive cases. On the other hand we are also seeing reports that people may be deleting or turning off the NHS tracing app because they are being pinged to isolate if they come into contact with a positive case and people do not want to do that. If that is the case it is also unlikely those people are getting tested, for the same reasons.


2/ The UK has actually reached herd immunity of a sort. Vaccination rates are high in the UK with almost 70% of the adult population double vaccinated and 87.9% having had a single vaccination. On top of this over 5.6 million people have had a positive test over the last 18 months although some of them are not adults. We can assume that the actual number of cases are significantly higher than this. Even if we just take the reported number and reduce it a bit for the younger people tested positive that is a further 10% of the adult population (which is 53 million based on the UK data). We have to discount for the fact that some people who have been vaccinated have subsequently tested positive. Also some people who have been infected will have got a vaccine subsequent to their infection . If we take as a rough guestimate that this balances out certain under-reporting of positive cases then over 90% of the adult population has some level of immunity and probably close to 80% of the adult population have immunity from double vaccination or being infected.

The next 2-4 weeks will show which of these explanations are true. Hospitalisations and deaths are lagging indicators so they will keep rising for a while because they reflect historical infections. Of course the removal of restrictions on so called “Freedom Day” will feed into higher transmission rates than would otherwise have been the case.

If we assume that herd immunity has been reached then what are the implications for Australia?

Before I outline those I want to clearly state that I am not a supporter of the UK government policy over the last 18 months. Leadership there has been abysmal and in my view borders on the criminal. Lots of people have needlessly suffered and died due to incompetence and negligence by their political leadership. If they have reached herd immunity that result in no way justifies the path they have taken to get there.

In my view it has been irresponsible to let the case numbers run as high as they have in the UK over the last two months. Even though raw vaccination numbers have been falling the UK still had 317,000 people getting their first vaccination in the week ending July 19th and over 1.2 million people getting a second vaccination. That is over 1.5 million people better protected than they were a week ago. Maintaining some public health measures while those numbers continue to rise seems the least that could be done.

In Australia we are currently in a situation with low vaccination rates. According to Our World in Data 12.5% of Australians have been double vaccinated and 30% have had at least one vaccination (note that this is of total population, not adult population, using the same data source the UK has 54% fully vaccinated and 68.5% with at least one vaccination. If we add people with immunity from infection on top of that the numbers are probably more like 62% and 75% respectively). We also have very low total case numbers so immunity from infection is very low. As of July 24th Australia only has 32,565 confirmed cases for the whole of the Pandemic. Even if the real number is triple the reported number it is still only 0.4% of the population. So we can ignore immunity from infection as a major source of protection.

The current outbreak in NSW appears to be on a knife edge with cases rising despite restrictions being in place:

source: ABC

and a major lockdown protest with thousands of people posing the risk of a superspreader event.

We are well away from any level of immunity that would create general protection. 62% of the total population with double vaccination is 16 million people. Currently it is 3.2 million people. According to the ABS there were 6,271,624 people in Australia aged 19 and under as of December 2020. This leaves 19,426,469 people above that age. If we want to achieve 62% of the total population double vaccinated and it is only those aged 20 and above then we need to double vaccinate 82% of the that population. If we want at least 75% of the total population vaccinated at least once and only vaccinate 20 yr olds and above that is 100% of them. if we drop the age to 15 and above then it becomes 92.5% of people.

The vaccination rates are clearly accelerating with 181,842 doses administered on Friday . Vaccinating 19 million people takes 38 million doses. With 11 million doses already administered, a run rate of 181,000 a day will take us another 21 weeks although we know that daily rates will fall off in the later stages so it will take longer than that.

The real world experience of the UK will be just as important as any of the modelling that we are able to do here in Australia.

My view from all of this is that:

  • We may need levels of vaccination at 90% of 15 years old and above if we are to attain stability and protection.

  • That will be very hard to obtain and even if we can achieve it, then it is at least 7 months away.

  • If the current outbreak is not contained in NSW then it is very dangerous to their citizens and for the entire country If that situation arises it is likely that very hard borders to the other states will remain for months.

  • We must wait longer than the UK to be in a situation where we remove restrictions in the face of community transmission.

  • We must consider vaccination as a requirement for doing certain things in the community as France has done. I do not believe that we should enforce mandatory vaccination, and I doubt the political will is there to do so but we can say that people do not have the right to make the decision to remain unvaccinated and endanger others in situations that would cause spread.

Paul Higgins

If you want to see more of what I do or contact me then go to: Emergent Futures

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P.S. I do not have any medical qualifications but I have experience as a large animal veterinarian in large scale disease outbreaks in animals. I also have experience in preparing for exotic disease outbreaks in animals in my previous role as a director of Animal Health Australia.