- Coronavirus herd immunity may be closer than we thought, according to some scientists. They have adapted their mathematical models to take into account real-life factors that impact the spread of the virus in a community.
- Some told The New York Times that herd immunity could be achieved once 50% of a community is immune to infection via exposure or vaccination — others believe the number could be significantly lower than that.
- Of note, none of these figures can be proven and there’s no study to demonstrate that herd immunity had been reached in any country, city, or community.
Nearly eight months into the pandemic and more than 22 million infections later, there is a combination of overlapping factors that make the illness challenging to contain. The world could have flattened the curve, but only some regions managed to cut the transmission rate successfully. And even some of those countries are experiencing new outbreaks as the virus circulates freely inside communities, especially in places where people do not respect the simple COVID-19 guidelines that could reduce the spread. Dr. Anthony Fauci said in a recent interview he expects life to return to normal in late 2021, and that a combination of public health measures and vaccines would be needed to control America’s COVID-19 epidemic. A few days earlier, Bill Gates said he expects developed nations to contain the illness by late 2021 as well, once vaccines are widely available.
What vaccines will do, assuming they’re effective and safe, is to hasten the herd immunity phenomenon that would significantly reduce the infection rate while preventing the emergence of massive outbreaks that are hard to manage. We could get to herd immunity the difficult and painful way, by letting the virus roam free and infect a large percentage of the population. Sweden went that route and found that you’d have to pay a heavy toll. Many more people would have to die for communities to reach herd immunity via infection. That said, it turns out that herd immunity might be a lot easier to attain for COVID-19 than initially believed, which could be the great news the world needs right now.
A series of distinct studies, some of which have yet to be peer-reviewed, indicate that COVID-19 immunity is a lot better than we thought. Even in the absence of antibodies, which are almost undetectable in asymptomatic and mild COVID-19 survivors, the body does elicit a robust immune response that could deal with subsequent exposure to the virus. While researchers can’t say how long the immunity lasts, there have been no cases of confirmed reinfection in the eight months since it all started in Wuhan.
Herd immunity works when a large enough percentage of the population is protected against an infectious disease via direct exposure or vaccines. Some say that COVID-19 herd immunity will be achieved once more than 60% or 70% of the population is immune. Unfortunately, those milestones are extremely difficult to achieve. But a new study says that percentage may turn out to be much lower than initially believed, as scientists have started observing herd immunity in communities that were hit hard in the early months of the pandemic.
The New York Times reports that more than a dozen scientists say the threshold might really be around 50%, or maybe even less than that. If that turns out to be accurate, then the pandemic might be easier to contain, especially once vaccines can be deployed widely. The estimates are based on “complicated statistical modeling of the pandemic” that take divergent approaches and offer “inconsistent estimates.” Therefore, herd immunity can’t yet be proven for any community. The Times explains that parts of New York, London, and Mumbai already have “substantial immunity” to the virus. They’re all large, densely-populated cities.
These scientists realized that the original 60%-70% calculation for herd immunity doesn’t take real-life events into account. That figure is said to have assumed that each community member has the same susceptibility to the virus, which isn’t the case.
“Herd immunity could vary from group to group, and subpopulation to subpopulation,” Yale Institute for Global Health Dr. Saad Omer said. It could vary by postal codes. A neighborhood of older people might have little contact with other people, but they’d be more likely to die. Teenagers may contact dozens of others, but they’d stay healthy. The researchers also observed that the virus rushes through densely populated cities, but it’s slower to infect suburban and rural areas.
Once these factors are accounted for in herd immunity studies, the herd immunity percentages fall. Some researchers say the figure could go as low as 10% to 20%, but those estimates come from a minority of researchers who talked to The Times.
If the first coronavirus wave infects the most susceptible people, immunity could be achieved even more efficiently than with a vaccination campaign, said Stockholm University mathematician Tom Britton. His model says that 43% is enough for herd immunity.
The average infection rate for New York is 21%, but it can go as high as 80% in clinics. Random surveys found rates to fall between those estimates, Columbia University’s Mailman School of Public Health Wan Yan told the paper. Scientists from Mumbai conducted a random household survey where they tested every fourth or fifth home for antibodies. They found that between 51% and 58% of residents in poor areas had antibodies, but that figure dropped to between 11% and 17% in other places in the city.
While researches are far from declaring herd immunity for these cities or neighborhoods, these locations have not seen additional surges in cases since the first wave.
It’s still unclear how immunity lasts or how a subsequent reinfection would impact an individual once immunity wanes. Also, regardless of the model chosen to map herd immunity, there’s one huge thing that’s not exactly addressed in any of the experiments The Times mentioned. Not all patients who recover from COVID-19 have high levels of neutralizing antibodies in their bloodstreams, and they might get false negatives in antibody surveys. This would directly impact herd immunity conclusions, but in a good way. The number of infected people in a community could be much higher than what researchers can prove with existing antibody tests.
Still, if any of these new estimates prove to be accurate, health officials may be able to implement new guidelines for future waves of infections. Also, immunization campaigns could use validated data from these studies to target specific groups of people and prevent future outbreaks.
On a related note, if COVID-19 herd immunity is reached at a lower percentage than initially believed, then even a vaccine that’s just 50% effective might be good enough for public use in the first immunization stages. Dr. Antohony Fauci said he hopes vaccine efficacy will surpass 75% while cautioning that we won’t know the figure until Phase 3 trials are complete.
The Times’ full report on COVID-19 herd immunity is worth a read, and it’s available at this link.