Herd immunity for COVID-19 may not be so far off after all, new model shows

NOTTINGHAM, England — Herd immunity, or the idea that if enough people become infected with COVID-19 it will lead to immunity on a wide scale, is often mentioned as a possible solution to this pandemic. That said, it’s usually waved off an unrealistic possibility. Now, a new study from Nottingham and Stockholm Universities suggests that herd immunity may not be as far off as we’ve been led to believe.

According to their new mathematical model, far less people need to be infected with COVID-19 in order to reach herd immunity levels.

That model, which was specially designed just for this study, categorizes people into different groups based on age and social activity levels. Once those factors are incorporated into herd immunity projections, the percentage of a population that would have to become immune drops from 60% to 43%.

However, the study’s authors caution their calculations are not exact; that 43% number should not be looked at as an exact value, or even the best possible estimate.

The authors also note that people who are more socially active are more likely to be infected with COVID-19. Similarly, they are more likely to pass the virus on to others.

Achieving herd immunity without vaccine

As mentioned earlier, herd immunity refers to a large percentage of people in a given area contracting an infectious disease and becoming immune to it. This, in turn, breaks the disease’s “chain of transmission” altogether. The term “herd immunity level” means the percentage of a given population that would have to develop immunity to an infectious disease, such as COVID-19, in order for the disease to stop spreading once safety measures (social distancing, face masks) are relaxed.


Generally, 60% has been proclaimed as the herd immunity level needed among populations to stop COVID-19. That percentage was agreed upon because it is the usually accepted percentage of a population that must be vaccinated against an infectious disease to stop an outbreak from occurring.

So, that 60% figure is based on the assumption that every member of a community is equally likely to be vaccinated and therefore immune. Of course, that’s clearly not what would happen regarding COVID-19 herd immunity, since there’s no vaccine. Instead, herd immunity for the virus would have to happen due to the virus spreading throughout a population.

“By taking this new mathematical approach to estimating the level for herd immunity to be achieved we found it could potentially be reduced to 43% and that this reduction is mainly due to activity level rather than age structure,” comments professor Frank Bell in a release. “The more socially active individuals are then the more likely they are to get infected than less socially active ones, and they are also more likely to infect people if they become infected. Consequently, the herd immunity level is lower when immunity is caused by disease spreading than when immunity comes from vaccination.

“Our findings have potential consequences for the current COVID-19 pandemic and the release of lockdown and suggests that individual variation (e.g. in activity level) is an important feature to include in models that guide policy,” professor Bell concludes.

The study is published in Science.

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