By Denise Chow-NBC News
[The United States this Friday reached
100 million doses
of the coronavirus vaccine administered during the term of President Joe Biden, who promised to reach that figure in his first 100 days in the White House.
He did it a month before the deadline.
This Friday,
Biden told reporters that his government could "double" the 100 million figure in the first 100 days, which is equivalent to 200 million
injections before April 29.
It is hoped that with increased supplies, the figure can be reached.
However, infections are beginning to rebound, and immunization efforts have become a race to life or death against the rise of new, more contagious and dangerous variants of the virus].
The key to winning the race, experts say, is not only that vaccines play an important role in preventing serious illness from COVID-19, but also that they
can prevent people from spreading the virus even when they don't know they are there. ill.
"The ideal vaccine would work in two ways: One prevents a person from going to the hospital, ending up in the ICU and losing their life," said Peter Hotez, co-director of the Vaccine Development Center at Texas Children's Hospital.
"But if the vaccine also stops the asymptomatic spread, then it could potentially be vaccinated to get out of the epidemic," he added.
The first signs have been promising so far.
The effect of vaccines on asymptomatic infections was a big unknown, but scientists say it will be crucial to ending the pandemic.
[Follow our coverage on the coronavirus pandemic]
Asymptomatic cases
, involving people infected with COVID-19 but who have no symptoms,
are estimated to
account for more than half of all virus transmissions,
according to a recent study published in the JAMA Network Open journal by researchers from the Centers for Disease Control and Prevention (CDC).
If vaccines can block asymptomatic infections, they could also significantly reduce overall transmission, offering hope that the virus can be contained soon.
Vaccines can protect against transmission by
lowering a person's viral load
, that is, the amount of virus present in the body, said Becky Smith, a professor of medicine at Duke University.
"In theory, reducing viral load should impede the ability to transmit to others," he said, "and even if it does not totally prevent transmission, it should reduce it significantly."
The attention to vaccines and transmission comes at an important time in the pandemic.
Although cases worldwide have declined for several weeks, some European countries are on the rise.
Spikes are also taking place in some parts of the United States, a worrying development given that many states have recently relaxed restrictions.
FEMA Announces It Will Pay Funeral Expenses For Pandemic Victims
March 18, 202100: 28
Concerns also persist about variants of the coronavirus, including strains that may be most contagious.
The government's top infectious disease expert, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said Thursday that the United States needs to vaccinate as many people as possible to prevent further outbreaks.
Part of that strategy depends on the effect the vaccine may have in reducing transmission.
Last week, new data from Israel, where nearly 60% of the country's nine million residents have received at least one dose of the vaccine, suggested that
the Pfizer and BioNTech vaccine is 94% effective in preventing asymptomatic infections.
Another study by researchers at the University of Cambridge in the UK revealed that a single dose of Pfizer's vaccine can reduce asymptomatic infections by
75%
.
The results, which have not yet been peer-reviewed, come from an analysis of some 4,400 tests performed on vaccinated healthcare workers in Cambridge over a two-week period in January.
In
Johnson & Johnson
trials
, the company's vaccine was found to be
74% effective
against asymptomatic infections.
And according to a report released in December by the Food and Drug Administration (FDA), early data suggests
Moderna's
vaccine
may also protect against asymptomatic infections,
but the company has said more research is needed.
More than 10 states in the country register a rise in COVID-19 cases despite the advance in vaccination
March 19, 202100: 30
Angela Rasmussen, a virologist at Georgetown University's Center for Global Health Science and Security, said the first results are "very promising."
However, he added that there are still some big unanswered questions.
"Based on the real-world data that we have so far, it appears that vaccines have an impact on asymptomatic infection," he said, "the real question, however, is how broad this will be."
And because vaccines are not 100% effective, it is possible for a small number of vaccinated people to become infected with the virus.
If that occurs and a vaccinated individual is asymptomatic, it is not yet known whether the person could spread COVID-19 to others, according to Rasmussen.
In a new comment published Thursday in the journal Science, Rasmussen and Saskia Popescu, an infectious disease epidemiologist at George Mason University in Virginia, detail why controlling "asymptomatic transmission" is critical to ending the pandemic.
Asymptomatic transmission includes both people who do not have symptoms and those who are presymptomatic, but who later develop symptoms.
"As more people get vaccinated, that will have a population-wide effect on transmission, but while most people at this time are not vaccinated, we have to be aware of the problem of asymptomatic and presymptomatic transmission," he said. Rasmussen.
[The United States plans to ship 2.5 million doses of AstraZeneca vaccine to Mexico]
Most scientists agree that
there are two main avenues out of the pandemic.
One of them is to reach a threshold known as
herd immunity
, that is, that enough people have developed antibodies as a result of being infected naturally or from vaccines, so that future outbreaks are unlikely.
The other requires
stopping the spread of the virus
to the point that even unvaccinated sections of the population run little risk of becoming infected.
The world's first baby with COVID-19 antibodies is born: her mother had been vaccinated
March 17, 202101: 56
If vaccines can protect against asymptomatic infection, they could help in the latter, but the two strategies should not be mutually exclusive, according to the expert.
"It's really a set of interventions," he said, "we have to think of ways to reduce transmission overall, and not rely solely on vaccines."
One of the ways to reduce transmission in general is to take into account the public health measures that have been applied throughout the pandemic, such as
social distancing
, the use of
masks
and
avoiding meetings
with unvaccinated people.
If the virus can be adequately contained, aspects of life could return to normal even though part of the population remains unvaccinated, Rasmussen said.
"We don't need to be at the threshold of herd immunity to relax restrictions," he said.
"If we can make the virus so rare in the population, there will be no risk that people will be exposed to it, whether or not they are vaccinated," he concluded.