WHO Repeats Warnings Against ‘Herd Immunity’ Assumptions As Countries Lift Lockdowns & Brace For Resurgence
Shoppers line up outside a flower shop on Mother’s Day after Geneva, Switzerland began a phased re-opening in late April.

As countries cautiously begin to lift lockdown measures, WHO Executive Director for Health Emergencies Mike Ryan has again warned that serological studies were presenting increasing evidence that a ‘herd immunity’ approach to mitigating the effects of further waves of infection would not be effective. 

Herd immunity occurs when a large enough proportion of the population becomes immune to a disease, thus forming a protective ring around those who are still susceptible to disease. In the early days of the coronavirus, a number of countries including the UK and the Netherlands had pursued a “herd immunity” strategy, assuming that once enough people had gotten infected with the virus and generated natural immunity, the spread of the virus would naturally peter out.

Early results from a number of sero-epidemiological studies have shown that the proportion of people who were likely infected in the first wave of the pandemic is anywhere between 5-15%, according to WHO COVID-19 Technical Lead Maria Van Kerkhove. 

For example, only 1 in 10 people had developed antibodies against SARS-CoV-2, the virus that causes COVID-19, in Geneva Switzerland three weeks after the peak of the first wave of infections, according to a study posted on 6 May on the preprint server MedRxiv. Children and teens (5-15 years) were infected at about the same rate as adults aged 20-49 years, the study indicated, although the rate of childhood infection still requires further examination. People over the age of 50 were the least infected. 

The study is also significant insofar as Switzerland was one of the countries with the highest rates of reported COVID-19 cases, per million population.

“Assuming that the presence of…antibodies measured in this study is at least in the short-term associated with immunity, these results highlight that the epidemic is far from burning out simply due to herd immunity,” wrote the authors.

COVID-19 May Be More Lethal Than Assumed – Large Proportion of Population Remains Susceptible

Observed Van Kerkhove, “These studies indicate to us that there’s a large proportion of the population that remains susceptible. And that’s important when you think about what may happen in subsequent waves or what may happen in potential resurgences.

“And so we have a long way to go with this virus, because the virus has more people that can be infected.”

The low rates of people with antibodies to the virus also means that it may be more lethal than some experts have claimed – insofar as there isn’t a huge pool of undetected minor or asymptomatic infections. 

In [the herd immunity] narrative, there was an assumption…that we’re really just seeing these [rare] weird cases and difficult cases. Under [this theory] we’ll demonstrate that most people have been infected [with mild or asymptomatic illness] and then this will all be over. We’ll go back to normal business,” said Ryan.

“Well, the preliminary results from epidemiological studies are showing the opposite. It’s showing that the proportion of people with significant clinical illness is actually a higher proportion of all those who’ve been infected  – because the number of people infected in the total population is probably much lower than we expected.

“This idea that maybe countries who have lacked [public health] measures and will all of a sudden magically reach some herd immunity, and we’ll lose a few old people along the way – this is a really dangerous, dangerous calculation, and not one I believe most Member States are willing to make,” added Ryan.

Svet Lustig Vijay, Tsering Lhamo, and Kyra Dupont/Geneva Solutions contributed to this story

Image Credits: HP-Watch/Svet Lustig Vijay.