The experience in the Brazilian city of Manaus reveals how mistaken, and dangerous, the herd-immunity-by-infection theory really is. 

As families around the world mourn more than two million people dead from Covid-19, the Plan B academics and their PR industry collaborator continue to argue that the New Zealand government should stop focusing on our managed isolation and quarantine system and instead protect the elderly so that they can reopen the border and allow everyone else to get on with their lives. 

Like their friends over at the Great Barrington Declaration, the Plan B’ers are arguing that the pandemic is manageable by the herd-immunity-by-infection route. They are even hosting another online symposium in February where some of the architects of the Great Barrington Declaration will get the chance to impress their astonishing views of the pandemic on 500 people who are willing to donate to Plan B’s cause. 

Should you need any further convincing, Brazil’s experience with Covid-19 shows it is past time to put Plan B and the Great Barrington Declaration to bed. Once and for all. 

Herd immunity by infection 

Briefly, then, how is herd immunity by infection supposed to work? The theory is that if enough young healthy people get infected, when they recover and are immune, it will be difficult for the virus to find new susceptible hosts and the pandemic will fizzle out. That’s why the Plan B’ers want almost everyone to be able to get on with their lives, free to get infected, while the vulnerable isolate until it’s safe for them to come out again. 

So how many people need to get infected to reach this nirvana? You might hear this referred to as the herd immunity threshold. One of the Great Barrington Declaration’s leaders is Oxford University’s Professor Sunetra Gupta who describes herself a theoretical epidemiologist. She’s done some modelling that suggested if we assume lots of people are naturally resistant to getting infected (there is no strong evidence for this), then the herd immunity threshold could be as low as 25%. As in, if a quarter of the community get infected and recover that’ll be enough for herd immunity. Others have estimated it at about 40%. To put those numbers in context, the herd immunity threshold for polio and mumps is about 80% and for measles 92-95%. 

Back in July, Gupta said that cities such as London and New York that were hard hit early in the pandemic have probably reached herd immunity and so shouldn’t experience a second surge. A couple of days ago London’s mayor Sadiq Khan stated that the city was in crisis, with hospitals treating 46% more patients compared to their first surge.

The lesson from Manaus, Brazil

Manaus is the capital of Amazonas state in northern Brazil. It’s the largest city in the Amazon, with a population of more than 2 million. In many ways, Manaus is the ideal case study for the herd-immunity-by-infection theory propagated by Plan B and the Great Barrington Declaration. The city’s population is mostly young and at reduced risk of dying from Covid-19. The first case of Covid-19 was confirmed there on March 13 2020. Its outbreak went largely uncontrolled, peaking in early May.

A study of blood donors suggests that by October, more than 70% of the population of Manaus had had Covid-19. That’s well above the predictions for the herd immunity threshold, so if the Plan B/Great Barrington Declaration lot are to be believed, the people of Manaus should be protected now, right? Before I get to that, let’s look at the cost they paid to get there. By May, the city had experienced four and a half times more deaths than they had the year before. Hospitals were overwhelmed. Mass graves had to be dug. Over 6,000 people died. 

Fast forward to January 2021 and Manaus and the Amazonas state are in the grips of a second surge of Covid-19. So much for herd immunity. There have been more than 24,000 new cases over the last two weeks. Hospitals are filling up and running out of oxygen. Meanwhile, President Jair Bolsonaro, a far-right former army captain and Covid-sceptic, has tweeted that people should seek early treatment with the anti-malarial drug hydroxychloroquine, a post that Twitter labelled as promoting misleading and potentially harmful information about Covid-19. 

A new Covid variant emerges

The Japanese ministry of health recently reported that it had detected a new SARS-CoV-2 variant in four travellers who arrived in Japan from Amazonas state at the beginning of January. Now a new study has looked at the genomes of 31 viral samples collected from patients in Manaus between December 15 and 23. Thirteen of the genomes belonged to this new variant, which they’ve called P.1. It’s a bit like the new strains recently identified in the UK and South Africa in that it has quite a lot of mutations including those that in combination may increase how infectious it is. 

So, is the new wave of cases in Manaus because infection doesn’t lead to long lasting immunity? Or because new variants of the virus are emerging that can evade the immune system? Or might it be a combination of both? That is what scientists are now trying to find out.

But let me be clear. These new viral variants are what we get when we allow uncontrolled community transmission of Covid-19 to happen. The same uncontrolled community transmission that groups like Plan B and the Great Barrington Declaration continue to advocate. Far from letting everyone get back to life as normal, we get overwhelmed hospitals and unnecessary deaths. All while providing the perfect conditions for the virus to evolve. 

Lots of countries around the world, including New Zealand, are showing that following an elimination strategy is best both for people’s health and for the economy. It’s time for the Plan B and Great Barrington Declaration proponents to follow the evidence and get on board.