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Wearing a mask can help stop transmission of SARS-CoV-2 that causes COVID-19. Matej Kastelic/EyeEm/Getty Images
  • The number of COVID-19 cases is decreasing, but experts aren’t sure why.
  • About 12 percent of people in the United States have had at least one vaccine dose, but that alone wouldn’t explain why cases have dropped so drastically.
  • The end of holiday get-togethers may be one reason why cases have continued to drop to their lowest levels since October in the United States.

Recent data shows that COVID-19 cases are finally decreasing after a winter surge that claimed thousands of lives and overwhelmed intensive care units across the United States.

Experts aren’t sure why the number of cases is dropping, but there are likely several contributing factors behind the recent dip.

Vaccinations in the most at-risk groups could be helping, and many of the people who engage in behaviors that make them susceptible to COVID-19 may have already been exposed to the virus.

If they got COVID-19 during one of the previous waves, they may have some degree of immunity.

Mostly, though, experts suspect the holiday season contributed to uncontrolled transmission. And now that the seasonal gatherings are behind us, COVID-19 isn’t spreading quite as rapidly.

“If we’re not having these big family gatherings, no holidays, anything like that, I think the opportunity to spread has decreased from that societal part as well as the biological part of people having immunity from the few people who have been vaccinated and the large amount of people who have actually caught coronavirus,” said Chris Thompson, an associate professor of biology at Loyola University Maryland’s Department of Biology.

The recent dip doesn’t mean we are in the clear. Cases could pick back up anytime, especially as new variants take hold.

According to a new report released by the Centers for Disease Control and Prevention (CDC) on Wednesday, Feb. 17, the emerging variants — like the B.1.1.7 lineage identified in the United Kingdom — could lead to a rapid rise in cases.

With all three waves that have occurred during the pandemic, we’ve seen a massive increase in cases that eventually, after a couple months of rapid spread, declined.

The latest surge picked up in October, around Halloween, when families started to gather indoors. Cases increased during Thanksgiving and then skyrocketed after Christmas and New Year’s.

Now that the seasonal gatherings are behind us, COVID-19 cases have started to drop off again.

Dr. Elizabeth Beatriz, an epidemiologist with the Massachusetts Department of Public Health and a COVID-19 adviser at Parenting Pod, said it’s important to note that cases are still high.

“The case rate is still high — even though we have had a significant decline in the past month, it is still higher than it was in the height of the pandemic last spring,” Beatriz said.

Beatriz suspects we’re now seeing the effects of people resuming safety precautions like mask wearing, physical distancing, and not attending as many gatherings with others.

Estimates suggest close to 28 million people in the United States have been diagnosed with COVID-19, and because so many asymptomatic and mild cases go undetected, that number is likely much higher.

Thompson said he thinks a lot of people who engage in behaviors that make them susceptible to COVID-19 have already recovered from the infection.

“A lot of those people were involved in the previous surges that we saw and so they may have immunity right now,” Thompson said.

Early evidence finds that immunity to COVID-19 may last for at least 3 months after infection.

More recent studies find immunity could last longer, persisting for 8 months if not longer.

While new coronavirus variants are on the rise, virologists think the antibodies produced against the original coronavirus will confer some degree of protection against emerging variants.

People who have worn high quality masks and remained at home are probably still adhering to precautions, which is keeping them protected, Thompson predicts.

“I think we may have kind of exposed most of the people who are going to get exposed,” Thompson said.

This doesn’t mean the country is close to naturally reaching herd immunity.

Rather, the people who are at greater risk due to behavior or the nature of their job have likely been exposed to the virus. If they were exposed and developed antibodies, this means they’re less likely to transmit the virus now.

This growing level of population immunity may be helping reduce transmission.

The vaccines are probably helping in reducing the number of COVID-19 cases, but not in a significant way at this point, according to health experts.

As of mid-February, approximately 12 percent of the U.S. population has had at least one vaccine dose, including those who are most at risk for COVID-19.

“Of the people who have been vaccinated, we are seeing a drastic decrease in the number of infections,” Thompson said.

However, Thompson said, if we look at cases across the entire population, there haven’t been enough vaccinations “to see that same trend extend globally.”

Thompson suspects the Biden administration has also shifted the way we think and talk about the pandemic.

The message has transformed from “this will go away” to “this can go away if we take certain precautions,” Thompson said.

Under Biden’s administration, there’s also been a big push to wear masks.

People are now required to wear masks while traveling, and double masking has been recommendation by the CDC.

The shift in national conversations could be encouraging people to be stricter with the mitigation practices used to prevent COVID-19.

Some infectious disease experts have suggested that, similar to the flu, COVID-19 could be a seasonal illness.

But flu season usually peaks around February or March, so seasonality probably wouldn’t make an impact until the weather warmed up.

“Influenza tends to peak right around Christmas time, so we’re still in prime influenza season and that’s very much a seasonal virus that we’re accustomed to,” Thompson said.

If the coronavirus were to be seasonal like the flu, we likely wouldn’t see a meaningful decline until next month.

Whatever the causes may be, this decline in reported cases doesn’t mean COVID-19 is fizzling out.

“It is possible, even likely, that as we ramp up vaccinations, resources and efforts are being shifted from testing to vaccinations,” Beatriz said.

Experts say it’s crucial to continue wearing a mask and practice physical distancing because there could be another spring surge, especially as emerging variants gain traction.

“As long as we can social distance, wear our masks appropriately, wash our hands, and stay home when we’re sick, we have a chance to mitigate this,” Thompson said.

Experts think the biggest factor for the drop in the number of COVID-19 cases is that people aren’t attending as many inside gatherings as they did during the holiday season.

Vaccinations in at-risk groups is probably helping a bit along with increasing population immunity amongst those who’ve already had COVID-19.

Still, experts say we could see another surge in the spring, and recommend that people continue to adhere to the safety measures known to effectively prevent COVID-19.