COVID-19: Collective immunity by vaccination could be delayed by impact of new variants

There are now 5 worrying variants of the coronavirus in the world, according to the World Health Organization. This means that there is evidence that these variants may be more transmissible, produce more severe disease cases, and could significantly reduce neutralization by antibodies generated during a previous infection or vaccination, among others. potential effects. At present, a surveillance for the appearance of variants is carried out, but there is a risk that they interfere in obtaining herd immunity – also called group immunity – through vaccination during this period. year, according to experts in epidemiology and infectology. .

It was calculated that by vaccinating 70% of the world’s population, virus circulation could drop significantly. But new variants may require reaching a higher percentage of the population. The percentage of people who need to be vaccinated depends on the basic reproductive number of each virus, better known as R. It indicates how many new cases are caused by each positive virus.

A year ago, the R for the coronavirus was estimated to be between 2 and 3, and that’s where the target of 70% came from. But now there are more contagious variants and the R can be between 3 and 5. A more communicable disease forces more people to get vaccinated. Maybe now 80% or 90% is needed, according to researcher Quique Bassat, of the Barcelona Institute for Global Health. In contrast, diseases such as measles are even more contagious than newer variants of the coronavirus. It has an R greater than 12 and requires the vaccination of more than 95% of the population to obtain herd immunity.

“The ideal is to vaccinate the entire susceptible population as soon as possible to reduce the circulation of the virus,” he explained to Infobae biologist Alejandra Capozzo, infectious disease researcher at Conicet and the National Institute of Agricultural Technology. “The more it circulates, the more the virus replicates, and the more likely it is to generate genome changes. As well as the current situation of the pandemic in terms of progress of vaccination plans, this year, there would be no collective immunity with vaccination ”, Tenuous.

Para Capozzo, There is a large barrier that could prevent herd immunity from being obtained in 2021 through vaccination. “It was not understood that the pandemic is a global problem. It is under attack at the regional level, and it does not work. Collective immunity can only be obtained by one country, unless travel abroad is absolutely blocked ”. The researcher specifies: “The necessary collective immunity is at the level of the world population. If we don’t think of it this way, variants can emerge that escape the action of current vaccines. For this reason, access to vaccines is essential in all countries ”.

Argentina is going through the second wave of COVID-19 and, despite the movement restrictions, the number of positive cases is worrying. The vaccination plan started in January, but proceeded slowly due to the lack of doses. In recent days, the country had the highest average daily infections, after India, Brazil and the United States, according to the specialist site Our World in Data. If we take the average of the last seven days, according to the daily reports issued by the Ministry of Health of the Nation, between May 10 and May 16, the daily number of infected people reported in Argentina was 22,792, with an average of 457 deaths. In the past week, the country has totaled 159,545 infections; the United States, 232,489; Brazil, 442,453 and India, 2.3 million, according to Our World in Data.

“No one is sure that everyone is not,” has been a phrase that has become popular in recent weeks. Although developed countries are more advanced in vaccination against COVID-19, the protection of their populations could be affected by the traffic that would continue in countries with less coverage.

The concept of collective immunity was described in a classic 1929 book: The principles of bacteriology and immunityby Topley and Wilson. They held that “The English herd is immune to plague and typhus, but only as long as individuals remain in the herd.” For the coronavirus pandemic, various estimates have been made.

The epidemiologist Zoe Hyde, biostatistics from the University of Western Australia calculated in The conversation that for a baseline reproductive number of 2.5, almost 100% of the population should be immunized with a 62% effective vaccine, such as Oxford / AstraZeneca, but 63% coverage might be sufficient if a vaccine is used. , such as Pfizer / BioNTech.

Meanwhile, Kamran Kadkhoda, an immunopathologist at the Cleveland Clinic in the United States, estimated that even with an effective base count as low as 0.99, a group immunity of 60% to 72% is needed to cut the chain. transmission. This estimate implies that 63% to 76% of the population should receive a vaccine with an effectiveness of 95% or 84% to 90%.

In the United States, which has accelerated since February with the vaccination, the possibility of having difficulty achieving the desired collective immunity is also being assessed due – among other things – to the resistance attitudes of some people. who will not apply the corresponding doses. Collective immunity in the event of coronavirus infection is said to be achieved with more than 80% of the population vaccinated in the United States. However, today this percentage is considered almost impossible to achieve by experts in public health and infectology. They even recognize that there is a possibility that the coronavirus will continue to circulate like the flu virus does during winters.

As of last year, the Chief Counsel on COVID-19 of the President of the United States, Anthony Fauci had stressed the interest of vaccination for public health because of the potential it has to reduce the spread. “This is not only good for you, your family and your community, but it will have a very big impact on the dynamics of the epidemic in our country,” he said.

Another problem is the large territory of the northern country. Even if nationally the vaccine coverage for COVID-19 reached 95%, there could be municipalities with a coverage of 70%. These differences could encourage further circulation of the coronavirus in these cities, which in turn could influence the epidemic as they are connected to other cities. Additionally, as a country, the United States also has connectivity with other nations and will increase them as travel restrictions are lowered. For this reason, specialists like Natalie E. Dean, a biostatistician at the University of Florida, stress that attention must be paid to the health of the populations of other countries. Because the new variants that appear could also arrive with travelers in the United States and spread.

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