Opinion: collective immunity is a fantasy


During ABC’s public meeting with voters on Tuesday, President Donald Trump said the coronavirus would “go away” even without a vaccine. “You will develop – you will develop a herd – like a herd mentality. It’s going to be – it’s going to be developed by the flock, and it’s going to happen. All of this will happen, ”he said.

It seems Trump meant herd immunity, rather than the ‘herd mentality’, but whatever – the line of thinking he was apparently trying to invoke goes like this: if Americans let SARS-CoV- 2, the virus that causes Covid-19, run amok, so eventually enough people will be immune (around 70-90%) that the virus no longer poses a threat to the population.

I have written before about the recklessness and ineffectiveness of this line of thinking, and many experts have agreed. The strategy would result in a catastrophic number of deaths in the United States. And Sweden, which has taken a lax approach to coronavirus restrictions, is still a long way from the collective immunity threshold. Thanks to researchers using genomic sequencing techniques, we now know that people can be re-infected with Covid-19 – a fact that should be the last nail in the coffin of any ill-conceived hope for herd immunity.

Human coronaviruses in general are not known to cause herd immunity. They infected us like clockwork for decades – many of us multiple times in our lifetimes. Until recently, it was not known whether this would be the case for SARS-CoV-2. Scientific case studies of two patients re-infected with Covid-19 – one in Hong Kong and the other in the United States (which is still subject to peer review) – have since answered this question. . The only one that’s left is how often the reinfection occurs.

What might shed light on this question is a multi-year collaborative study by researchers from the Netherlands and Kenya on the human coronavirus NL63 (HCoV-NL63), a member of the coronavirus family that is not fatal but is endemic to people around the world. . Like other non-lethal human coronaviruses, which probably infect us all at least once in our lifetime, HCoV-NL63 causes what we would call a cold. Three key findings from this study, which was published in 2018, may help us better understand the Covid-19 SARS-CoV-2 virus and its ability to re-infect us.

The study was conducted in homes and hospitals in Kilifi County, Kenya, where researchers followed the circulation of several coronaviruses in the community over a six-year period. The first relevant result is that some patients were not re-infected once, but twice. One person has even contracted the virus four times. This tells us that immunity to HCoV-NL63 was short-lived – so much so that some were re-infected in as little as three months.

The second significant finding was that a surprising number of patients had higher viral loads during reinfection than during primary infection. For most people, the amount of the virus in their body and the severity of their symptoms decrease from infection to infection. But for some patients in the NL63 study, the reverse was true. This appears to be the case for the 25-year-old man from Nevada who was re-infected with Covid-19.

In fact, researchers in the NL63 study postulated that the elevated levels of antibodies in some Kenyan patients increases the likelihood of infection rather than preventing or mitigating it – a finding that defies the more general expectation that a strong immune response would mean greater protection against reinfection. These cases suggest that no one who contracts a coronavirus, regardless of the nature of their primary infection, is completely immune from reinfection.

The third significant finding is that in six years, herd immunity to HCoV-NL63 was never acquired and the virus continued to persist for the duration of the study. Granted, endemic human coronaviruses are not as contagious as SARS-CoV-2, but they have been infecting people all over the world for decades and still manage to come back. Even if SARS-CoV-2 becomes an endemic human coronavirus like HCoV-NL63, we will not be rid of the dangers it presents to vulnerable populations – unless we have a widely used vaccine that can help us. give the protection of our natural immune response can not.

It is in our best interests to recognize the risk of reinfection – rather than hoping for herd immunity – when thinking about the scientific and public health interventions we will need in the months and years to come. We must devote most of our efforts to the development and equitable distribution of a vaccine that is not only safe and effective, but which takes into account the possibility of re-infection. We need to redouble our efforts to organize evidence-based public health interventions until a vaccine is available. Otherwise, it will be a long time before we see the last Covid-19 – and not long at all before we are once again defeated by another deadly coronavirus.


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