The Delta variant of Covid-19 is as contagious as chickenpox, probably has more serious effects than its predecessors and infected people seem to transmit it as much whether they are vaccinated or not, according to official US documents.
To discover
Covid-19: what we know about the Delta variant
Read also: Covid-19: is the Delta variant as contagious as smallpox?
These findings, which are based on scientific studies, appear in a presentation circulating internally within the Centers for Disease Prevention and Control (CDC), the main health agency in the United States. Revealed by the Washington Post, these documents, whose authenticity has been confirmed to AFP, are accompanied by a warning to those responsible: "
the war has changed
".
CDC director Rochelle Walenksy relied on the data in the presentation to re-recommend, for two days, indoor masks for people vaccinated in high-risk areas. The presentation is based in particular on an analysis conducted in Provincetown, Massachusetts, where nearly 900 cases of Covid were detected after the July 4 National Day festivities, although three-quarters of the participants in the event have been vaccinated.
However, there was "
no difference
" in the viral load of vaccinated or unvaccinated people, according to the presentation of the CDC, which seems to indicate the same degree of contagiousness regardless of the vaccination status. In contrast, there have been few hospitalizations (seven to date) and no deaths related to this outbreak, according to local news site Masslive.com.
This observation "
is the main factor in the change in the recommendations of the CDC
" on the mask, explains to AFP Céline Gounder, specialist in infectious diseases at New York University: "
It is not to protect vaccinated people who , if they are infected, will have mild symptoms or none at all, but they can be found to infect other people.
"
Vaccination campaign
Jennifer Nuzzo, epidemiologist at Johns Hopkins University, adds that it should be noted that the Provincetown event occurred in a location where community transmission was low;
as such, the new recommendation of the health authorities on the mask would not have been applied.
"
In addition, information on this event suggests that exposure (to the virus) was likely in places like bars or house parties, where wearing a mask would be unlikely,
" she told AFP. In addition, CDC documents show that contaminations of vaccinated people are not as rare as previously thought with "
35,000 symptomatic infections per week out of the 162 million Americans vaccinated
."
Based on international studies, the CDC judge that the Covid was initially about as contagious as the flu, but has become comparable to chickenpox - one person infected with the Delta variant transmitting it to eight others on average - still in below measles.
Data from Canada, Singapore and Scotland suggest it could be more dangerous, with more hospitalizations and deaths.
Read also: Measles, much older than we thought
The effectiveness of vaccines varies, but in their presentation, the CDC estimates that the risk of dying or being seriously ill is divided by ten with a vaccine and the risk of being infected by at least three, which is to say that the vaccines are 90% effective against severe forms and 67% against infections.
For experts, vaccines therefore remain the solution to the health crisis.
The vaccination campaign in the United States had run out of steam, but the White House announced that half a million people received their first injection on Friday, the highest since July 1.
Just under 50% of the total population is now fully vaccinated.