Last week, President Joe Biden said his government’s goal is to get the country “closer to normal” by the fourth of July.
Although it appears that the United States is moving in the right direction – most people over 65, for example, have received at least one dose of a vaccine – scientists tracking the pandemic say that, to get a national view, it is fundamental to look separately in each state, even in each city.
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“If you look at this as a type of monolithic event, you will miss out on a lot of details,” said Dr. Thomas Giordano, head of infectious diseases at Baylor College of Medicine in Houston.
Giordano sees the Covid-19 outbreak in the United States as a “series of micropandemics”.
“What is happening in Houston is not the same as what happened in New York City or in Phoenix or LA,” he said. “They had different curves, different mortality rates.”
A variety of metrics can indicate that the country is controlling the pandemic, including the number of new daily cases and the number of deaths. But epidemiologists say that three specific indicators are needed to gain a clear understanding of the country’s overall response: the number of hospitalizations related to Covid-19, the so-called virus reproduction number and the number of vaccinations administered.
Hospitalizations
For months, scientists have relied on the number of positive Covid-19 tests done in a given community – known as “percent positivity” – as an indicator of the severity of the outbreak.
But over time, this metric may lose importance. The percentage of positivity will change based on how many people are tested, said Giordano. The number of tests “will decrease as we vaccinate more people,” he said, “and people will be less inclined to be tested.”
One way around the problem is to focus instead on hospitalizations related to Covid-19.
“The hospitalization rate, for me, is the hardest and fastest number,” said infectious disease specialist Cameron Wolfe, an associate professor of medicine at Duke University School of Medicine.
No matter what we have done in the past year, we have not greatly reduced the chances that a person receiving Covid will need hospital support.
“No matter what we have done in the past year, we have not greatly reduced the chances that a person receiving Covid will need hospital support,” said Wolfe. This means that hospitalizations continue to be a good representation of general cases in any community.
Hospitals also continue to test Covid-19, providing another snapshot of the spread of the community.
“Every hospital in the country is testing every patient who arrives in Covid-19,” no matter what problem brought the patient to the hospital, such as a heart attack, said Dr. Timothy Brewer, an infectious disease specialist and professor of epidemiology at UCLA Fielding School of Public Health.
“People who are sick enough to go to the hospital will, regardless of whether or not they are concerned about Covid,” said Brewer.
Reproduction number
The reproduction number of a virus indicates how many people a single sick person can infect.
Scientists generally calculate the number based on several factors: how many people remain susceptible to a disease, how many people are currently infected and how many have some level of immunity, either through infection or immunization.
The number of reproduction can be calculated in different populations, for example, at state or municipal levels, and can fluctuate over time.
The lower the number, the better – and less than 1 is the best.
A reproduction number above 1 means that a sick person is likely to transmit the virus to at least one other person, said Dr. Richard Medford, associate director of medical informatics at UT Southwestern Medical Center in Dallas. (A reproduction number 2, for example, means that an infected person will transmit the virus to two other people.)
This is a problem, as it indicates that the outbreak will continue to worsen. “If we see the number of reproductions increasing, we will be concerned,” said Medford.
On the other hand, if the number is less than 1, it is an indication that the community is in better shape. This would mean that it is unlikely that a single person will pass the virus on to one or more people.
Vaccines
In the long run, the metric that will most indicate the country’s progress is the number of vaccines administered.
“How many vaccines can we put on guns? This is how I can determine how well we are doing,” said Medford.
On Wednesday, the Centers for Disease Control and Prevention reported that 111 million vaccines were administered across the country. But scientists say it is important to detail the gross number to find out who is actually rolling up their sleeves.
“You cannot really look at overall vaccination rates without making sure that all populations have the same level of vaccination. Otherwise, you may be having small outbreaks,” said Dr. Peter Chin-Hong, a disease specialist. infectious diseases at the University of California, San Francisco.
There may be significant variations in the distribution of the vaccine in different areas of the country, as well as in communities of color. These details will provide a critical context for epidemiologists to interpret vaccination numbers in the coming months.
Medford said he also likes to look at vaccines by age. “When you look at severity in terms of how many people have been hospitalized or how many people have died of this disease, the most important thing is to vaccinate our elderly people,” he said.
And the faster vaccinations are implemented, the more chances the country will be able to stay ahead of emerging variants, especially variant B.1.1.7, which was discovered in the United Kingdom.
“This new variant, which is taking control of the United States, is more transmissible,” said Murphy. “This increases the proportion of people who need to be immune.”
What about the herd’s immunity?
The more people are vaccinated, the closer the United States gets to collective immunity – the point at which enough people are immune to the virus and it can no longer spread. Immunity can come from both vaccinations and previous infections.
But the true number of infections in the United States can be difficult to determine, because many people who were ill have never been tested. As a result, the epidemiologists with whom NBC News spoke preferred to focus on vaccination numbers.
“It’s an absolute number,” said Medford. “I can, without a doubt, say how many people have been vaccinated and I know how effective these vaccines are.”
The jury has not yet decided on the so-called critical vaccination threshold – the percentage of the population that must be vaccinated to protect everyone else – and can be a moving target.
Last year, for example, experts estimated that the United States needed to vaccinate 60% of the population. But, as the virus changes to spread more easily, the percentage should increase.
It is now “close to 80 percent, just because variant B.1.1.7 is more transmissible,” said Bill Hanage, associate professor of epidemiology at the Harvard TH Chan School of Public Health. “You need to have more immune people to stop” the spread.
The evidence has shown that current vaccines are effective against variant B.1.1.7 – even if the vaccines are not perfect.
“We don’t need 100 percent success. We need a solid 50 to 90 percent success,” said Giordano, referring to the effectiveness of the vaccines. “If enough people are 50% successful, the chances of a person getting really sick from Covid are lessened.”
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Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, advised caution about using the term “herd immunity” during a congressional hearing on Wednesday.
“We really need to be careful with this elusive terminology,” said Fauci. “We should focus on vaccinating as many people as possible as soon as possible,” he said, rather than focusing on an “arbitrary percentage”.
Ultimately, no single measure will determine when life can return to “normal”.
“I don’t think there’s a metric that says, ‘Oh, it’s over,'” said Justin Lessler, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, referring to the pandemic.
SARS-CoV-2, the virus that causes Covid-19, is probably here to stay, but is expected to slowly become more like the flu, which requires annual boosters.
That is, instead of an on / off button, the end of the Covid-19 emergency in the USA will be more or less on a dimmer.
“He will become more of an old enemy than the scourge he is today,” said Lessler.
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