Throughout 2020, major holidays in the United States were quickly followed by surges in COVID-19 cases, hospitalizations, and eventually deaths.
For example, in the days following Memorial Day in 2020, at least 14 states hit a new record in daily new COVID-19 cases.
This year, things look different.
Approximately 52 percent of the total U.S. population has received at least one dose of a COVID-19 vaccine. On top of that, millions of Americans — more than 33 million— have contracted the coronavirus and likely have some degree of natural immunity.
The current level of immunity in the population — from both vaccination and previous infection — seems to have been enough to stave off a surge following Memorial Day gatherings this year.
This does not mean the pandemic is over or that COVID-19 is not a risk, especially to not vaccinated people.
We will continue to see new COVID-19 cases.
But by vaccinating the most vulnerable people first, we essentially took away the likelihood that COVID-19 will overwhelm our hospitals like it did in 2020.
New data shows that positive COVID-19 tests have fallen to the lowest recorded rate and that hospitalizations and deaths have continued to decline despite holiday gatherings steeply.
Data has consistently found that COVID-19 vaccines are very effective at preventing severe illness.
Preliminary evidence also suggests that natural immunity, or immunity conferred from prior infection, also appears to be long-lasting.
Together, the immunity from vaccines and prior infection have staved off spikes after Memorial Day weekend.
“Both of those factors — natural immunity and vaccine-induced immunity — work together to make it harder for the virus to find new people to infect. The higher those numbers are, in combination, the more obstacles the virus is going to find when it tries to spread from person to person,” said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins University Center for Health Security and an infectious disease expert.
As more people become immune, there will be even less opportunity for COVID-19 to spread and reach unvaccinated people.
Will there be spikes in unvaccinated communities?
Unvaccinated people are still susceptible to contracting the coronavirus and developing COVID-19.
Reports from hospitals show that virtually all people currently hospitalized for COVID-19 are not vaccinated.
Unvaccinated people may benefit if enough people get immunized that the United States can reach herd immunity.
But we’re not there yet.
It’s crucial to get the shot, especially since some coronavirus variants circulating contain mutations that appear to make the virus more transmissible among unvaccinated people.
“We still may see cases increase in places where there is low vaccination and low natural immunity,” Adalja said.
For example, in some counties in Mississippi where only 14 percent of the population has been fully vaccinated.
It’s unknown what the percentage of natural immunity is, but there may be more cases if there isn’t much natural immunity.
If a large portion of Mississippi’s population previously had COVID-19, as the state’s governor recently stated, then there’s hope this may help slow or prevent a new surge.
However, relying on natural immunity can be dicey since reinfection is possible. Additionally, COVID-19 was never so widespread that a majority of the population developed the disease.
Dr. Monica Gandhi, an infectious diseases specialist with the University of California, San Francisco, pointed out that Los Angeles County has a relatively high vaccination rate, with 66 percent of the population getting at least one dose.
In early March, a study from the state health department found that 45 percent of residents had antibodies either from exposure to the virus or through vaccination.
In early March, COVID-19 vaccines were not widely available to people under 65, so a significant portion of the antibodies was likely from exposure to the virus.
When you look at the high vaccination rate in Los Angeles County and then “add in the fact that 45 percent of county residents have been exposed before the rollout of the vaccine in the general population, you have natural immunity plus vaccine immunity in that county — and no, they did not and are not going to surge after Memorial Day,” Gandhi said.
We don’t have the seroprevalence studiesTrusted Source, or percentage of people who have coronavirus antibodies, to determine what natural immunity may be like across the United States, so it’s difficult to predict exactly how susceptible any state or county is.
While there is no way for us to calculate that as of now, but it is likely that states that had large surges — such as Texas — have more natural immunity, said Gandhi.
Adalja focuses more on hospitalizations and deaths rather than cases.
“Cases are less important. The goal of the vaccines… was to remove the ability of the virus to cause severe disease, hospitalization, and death,” Adalja said.
After Memorial Day weekend in 2020, new cases were followed by a spike in hospitalizations, which pushed some hospitals to the brink.
That’s no longer an issue this year in the United States. The group at the highest risk of COVID-19 is people over the age of 65.
That population has the highest rate of vaccination, with nearly 87 percent at least partially vaccinated.
As a result, we’re less likely to see hospitals reach their capacity after holiday weekends in 2021.
Experts say we will still see some new cases because the virus is still circulating. Still, natural immunity and vaccine-induced immunity have essentially prevented COVID-19 from being able to threaten hospitals again.
But cases, even if there are slight increases in certain areas, are “not going to necessarily translate to what happened in the past because of the way the vaccine has been rolled out to those high-risk populations,” Adalja said.
Throughout 2020, major holidays in the United States, such as Memorial Day weekend, were quickly followed by surges in COVID-19 cases, hospitalizations, and eventually deaths.
This year, we didn’t see a surge following Memorial Day weekend, thanks to the high level of vaccine-induced immunity and natural immunity across the U.S. population.
Though we will continue to see cases, health experts say that we have removed COVID-19’s ability to push our hospitals to full capacity by vaccinating people at risk of hospitalization and death.
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