For the past two weeks, the trend has been clear: new cases of coronavirus and hospitalizations are falling in the United States, even though the total number of daily positive cases is much higher than in the summer.
According to experts, the reasons for this improvement range from respecting barrier gestures (wearing a mask, physical distancing) to the fact that the holiday season, favorable to gatherings, is far away.
And, at least in some states of the country, the virus has already infected a good part of the population. But the situation remains precarious and too rapid easing of restrictions could upset the current balance, and trigger a new peak in the epidemic which has already killed more than 430,000 people in the United States, scientists worry.
The post-vacation peak is over
After a lull during the summer, the contamination rate soared again in the United States in the fall when, with the drop in the thermometer, people gathered in closed places, where they began to drop. the guard.
Then came the holiday season – Thanksgiving, Christmas, New Years – and family and friends reunions, which sparked a new wave of coronavirus.
In mid-January, the United States recorded an average of more than 250,000 positive cases and more than 130,000 hospitalizations per day, according to data from the Covid Tracking Project.
There are still currently more than 3,000 deaths per day, due to the delay between hospitalizations and deaths, but the curves are pointing in the right direction.
“The travel period that the virus has exploited is almost over,” Amesh Adalja of the Johns Hopkins Center for Health Security told AFP.
More careful people
The spread of epidemics is linked to human behavior.
Biostatistician Natalie Dean, an infectious disease specialist at the University of Florida, told AFP that she noted “a feedback mechanism in the population, which takes action when numbers rise in her area.”
She cites Florida, Texas and Arizona, three very lax prevention states where infections slowed after exploding during the summer, thanks to “political measures or several small changes in attitude.”
Brandon Brown, a public health specialist at the University of California, also points to “the decline in disinformation” about the epidemic because “it is difficult to deny the reality of the more than 400,000 dead.”
But if the population is becoming more cautious with the rise in cases, the reverse is also true, warn experts.
Immunity still to be done
The United States has so far recorded around 25 million confirmed cases of the coronavirus, an underestimated figure that could actually be between 100 and 125 million, according to Jay Bhattacharya, professor of medicine at Stanford.
It is proven that infected people have a high degree of immunity for some time. In addition, around 21 million people currently enjoy partial immunity after receiving at least one dose of the vaccine.
In total, this could represent some 40% of the 330 million inhabitants, but we are still far from the goal of 85% to achieve real collective immunity.
The vaccination campaign in nursing homes has likely contributed to the drop in hospitalizations and deaths from Covid-19, says Dr Adalja.
Some sparsely populated states are also approaching this immunity. Jeffrey Shaman, an epidemiologist at Columbia University, has modeled the impact of the coronavirus and estimates that “50 to 70% of the population of North Dakota has been infected.”
An extreme case, but Dr Shaman explains that between the rise in immunity in the population and the current adherence to health measures, the epidemic “should be containing itself by now.”
Like Dr Bhattacharya, Jeffrey Shaman is worried about a drop in precautionary measures in the spring, when population movements will resume and could upset this fragile balance.
There are also mutations in the virus. The more transmissible British, Brazilian and South African variants could increase the level needed to ensure herd immunity and, in the case of the South African variant, pose a more serious threat of reinfection.