Covid: why mass immunity can be ‘utopia’ with variants, according to experts

The term “collective immunity” appeared in the first months of the Covid-19 pandemic in 2020.

It is achieved when a sufficiently large number of people have already had a certain disease and developed antibodies or when a significant percentage of the population has been vaccinated.

Under these conditions, the probability that an infectious agent continues to circulate in the population decreases considerably, leading to the extinction of possible outbreaks (or pandemics).

The exact numbers vary by microorganism. Some diseases require a higher percentage of immunity—naturally acquired or gained through vaccines—than others.

Covid-19 has proven to be one of these more complex cases. Even with ongoing vaccination programs, the Sars-CoV-2 virus continues to circulate in some regions.

It cannot be said that so-called “herd immunity” has been achieved and, according to experts consulted by BBC News Mundo, the BBC’s Spanish-language service, there are several factors that make it unlikely.

Regardless of the future scenario, however, experts point out that vaccination and control measures remain powerful tools for advancing the fight against Covid-19.

Below are some of the reasons cited by experts who believe that collective immunity against Covid-19 can be a “utopia”.

The evolution of the virus

In the two years of the pandemic, Sars-CoV-2 evolved into variants that, in some cases, allowed the virus to become more contagious and a little more resistant to vaccines.

The clearest example is the delta variant, which has been shown to be at least twice as transmissible as the original virus.

As for the omicron, the first studies show that it may have a greater capacity to escape immunity.

To date, vaccines have been shown to be effective in significantly reducing the risk of developing a severe form of the disease and the risk of death.

Vaccinated people, however, can contract the virus and pass it on to others, albeit to a lesser degree than unvaccinated people.

This is the first complicating factor.

“With the vaccines we have, even if they reduce transmission, the concept of herd immunity doesn’t make sense”, says Salvador Peiró, a doctor specializing in public health and a researcher in pharmacoepidemiology at Fisabio, a Spanish organization that promotes research.

With the transmission rates seen with the omicron, he adds, the idea makes even less sense. Thus, although vaccines save lives, they cannot stop the virus from continuing to circulate, even if on a smaller scale.

And the fact that the virus continues to circulate creates a second complication: as it continues to transmit, there is the possibility of new, more contagious variants emerging, producing more severe symptoms or circumventing the effect of vaccines.

“Any place with a large number of infections, whether vaccinated or not, is a potential source of new variants”, points out Caroline Colijn, researcher in epidemiology and evolution of pathogens at Simon Fraser University in Vancouver, Canada.

Colijn recalls that Sars-CoV-2 also infects animals — so other species can act as a “reserve” for the virus until, at some point, it is reintroduced into humans.

decreasing protection

Another relevant factor is the fact that immunity acquired with the vaccine or after contact with the virus decreases over time, as indicated by the US Centers for Disease Control, the CDC.

According to Shabir A. Madhi, dean of the Faculty of Health Sciences at the University of the Witwatersrand in South Africa, the immune response after an infection or vaccination lasts between six and nine months.

But that period may change with the emergence of new variants — that’s why booster doses are being applied in several countries.

Uneven vaccination

And then there is the issue of uneven distribution of vaccines.

In countries like the United States and the United Kingdom, around 70% of the population is already vaccinated with two doses. Globally, however, just over half of the population received at least one dose.

In the lowest-income countries, only 6.3% received a dose, according to information from the Our World in Data platform.

This increases the risk that the virus will continue to spread and that potentially dangerous new variants will emerge.

“We’re not going to get over that by vaccinating rich countries every 6 months,” says Colijn.

“It is extremely important to take a global view and ensure that vaccines are available and used in all parts of the world.”

In essence, it is useless for a country to be fully protected while other regions of the world remain vulnerable, because the virus does not respect borders.

Utopia

“Hed immunity for Covid-19 is a utopia,” says Mauricio Rodríguez, a professor at the Faculty of Medicine at the National Autonomous University of Mexico (Unam).

According to him, collective immunity applies to small or delimited groups.

“The problem with covid is that it is present in all age groups, in all populations, in all places, all the time”, he adds.

What is the exit?

According to specialists consulted by the article, instead of aspiring to the total suppression of the virus, efforts should be directed towards making the world get used to living with the virus, without it representing a serious threat to humanity.

The goal is for it to become an endemic virus, that is, to continue circulating in the population, but at a level considered manageable.

Reaching this point is what Peiró calls “having functional control over the pandemic”.

“It is not about eliminating all cases, what we hope is to have a framework with very few serious cases”, says the specialist.

“It’s not that people aren’t infected, it’s that hospitals aren’t filled with serious cases.”

Peiró says the idea is for covid to look more and more like a cold.

“The pandemic’s success is seeing hospitals empty of covid cases.”

Immunity in practice

Colijn, for his part, agrees that collective immunity is unlikely to be achieved, but says that it is possible to obtain “collective immunity in practice”.

This means that if vaccines are applied massively and equitably, near-normal levels of activity can be achieved without the need for more radical measures such as lockdowns.

“We have to think about what measures we are willing to keep forever, maybe some of those measures are the use of masks or rapid tests.”

“Stopping seeing our friends or family is probably not one of those measures, we can’t do this forever.”

To achieve this “herd immunity in practice” and “functional control of the pandemic”, experts agree that it is important to prioritize the most vulnerable groups in vaccination campaigns.

The idea is to ensure that as many people as possible are protected from serious illnesses.

“Vaccines allowed us to fight the pandemic almost without restrictions”, says Peiró. “In other circumstances, we would all be locked up, with more deaths and more hospitalizations. But we are facing the delta with everything open, thanks to the vaccines.”

This scenario of combination of massive vaccination and equitable maintenance of care is approaching the stage the pandemic appears to be entering.

“We are in a transitional phase, going from an emergency stage to an endemic stage, which is when the virus will be circulating more regularly,” says Rodríguez.

“We must not panic, we must learn to live with the virus.”