5 Things We’ve Learned from COVID in Three Years

Three years ago, on March 11, 2020, Tedros Adhanom Ghebreyesus, director general of the World Health Organization (WHO), announced that the coronavirus that causes COVID was spreading worldwide and that the outbreak was officially a pandemic. At the time, there were more than 118,000 confirmed cases of COVID and 4,291 official deaths.

“In the days and weeks ahead,” Ghebreyesus said in a press conference at the time, “we expect to see the number of cases, the number of deaths and the number of affected countries climb even higher.”

Three years later the WHO has recorded more than 6.8 million COVID deaths, though studies of global excess mortality, or deaths above and beyond the expected amount in a given time, suggest the actual number is more than double that amount. In the U.S., there have been an estimated 1.1 million deaths from COVID, according to the U.S. Centers for Disease Control and Prevention. Long COVID, which occurs when people experience lingering or new symptoms even after recovering from the initial infection, has also emerged as a threat that is still mysterious, though doctors are increasingly honing in on possible causes and treatments.

The most at-risk populations now are individuals with preexisting chronic illnesses whose health is fragile and for whom hospitalization is a regular occurrence, says Jeremy Faust, an emergency medicine physician at Brigham and Women’s Hospital in Boston. COVID is one more factor that can push those individuals toward death. As a result, the pandemic is still causing excess mortality in the U.S. Mortality fluctuates from month to month but was approximately 10 percent higher in November 2022 than it was prepandemic, Faust says.

If March 2020 was like a flood, Faust says, today the world is no longer drowning. But the new normal is just a bit worse than before, he says: “Sea level is just higher,” Faust adds.

There is greater awareness now that a pandemic virus can rock societies, says Amesh Adalja, an infectious disease physician and senior scholar at the Johns Hopkins Center for Health Security. That awareness has not always translated to action, however. “It’s still not highly prioritized by policy makers, and there are really big questions about how the U.S. could respond” to a future pandemic, Adalja says. Public health missteps in the 2022–2023 monkeypox outbreak, ranging from poor access to testing to clumsy vaccine distribution, echoed those early in the COVID pandemic, he says.

“Until [infectious disease] is prioritized in a way that national security is, I don’t think you’re going to see full resilience,” Adalja says. “What you need is a proactive, sustained approach that doesn’t just last an election cycle.”

Despite the challenges of building preparedness, we have learned some hard-won lessons about SARS-CoV-2, the coronavirus that causes COVID, that could inform our approach to future pandemics—and public health in general.

mRNA Vaccines Are Safe, Powerful and Effective

One of the unambiguous successes of the response to the COVID pandemic was the rapid development of effective vaccines.

The pandemic was the first large-scale test for mRNA vaccine technology, which proved safe and effective against severe disease and death even as the virus evolved to form new variants. A recent analysis by the Commonwealth Fund, an independent research group that focuses on health care issues, found that in the two years after vaccines were introduced in the U.S., the shots prevented an estimated 18 million hospitalizations and three million deaths.

Masks Work

Masks and mask mandates became a political flashpoint during the pandemic, but the evidence shows that they slow the spread of COVID and other respiratory illnesses. For instance, according to the CDC, at least 10 studies as of late 2021 found that after local authorities implemented universal masking mandates, infection rates declined.

The best protection comes from high-quality N95 and KN95 masks. An influential publication in February 2022 in the CDC’s Morbidity and Mortality Weekly Report compared people who had tested positive for COVID and people who had not and assessed their mask-wearing habits. Among 534 participants who reported their mask type, a consistent cloth mask usage lowered the odds of testing positive by 56 percent, surgical mask wearing lowered the odds by 66 percent, and N95 or KN95 usage lowered the odds by 83 percent. Masks are most effective when they are sealed well, worn correctly and layered with other precautions.

Indoor Air Quality Matters 

In early 2020 no one knew how the virus spread, and the CDC and other health agencies around the world were sending out mixed messages. Hand sanitizer became a national obsession. People wiped down their groceries or left them overnight in their garage.

But research would soon confirm that the virus primarily spread through the air rather than via surfaces. This realization has triggered an interest in improving indoor air quality through both ventilation (letting outside air in) and filtration (cleaning the air of particles and pathogens). Research has found that continuous high-efficiency particulate air (HEPA) filtration can remove the vast majority of COVID viral particles in the air and dramatically lower exposure. And the effect isn’t limited to COVID: filtration removes other viral particles such as flu from the air, too.

Wastewater Tracking Is Useful for COVID and Other Diseases

The idea to track viral spread through wastewater first arose early in 2020 and has now become a national program. Wastewater has provided up to several weeks’ warning of coming viral surges because people begin to shed SARS-CoV-2 before they feel symptoms or seek medical care. Wastewater tracking is now integrated into other disease surveillance. Scientists have used sewage to track surges of viruses such as RSV and influenza.

Genomic Surveillance Is Key for Tracking Viral Evolution 

SARS-CoV-2 does not remain static. Over the past three years, variants such as Delta, which caused a surge of disease and severe illness in 2021, and the extremely transmissible Omicron, which spread rapidly in late 2021 and is still the dominant variant worldwide, have changed the course of the pandemic. Variants rise and fall in dominance as they outcompete one another to spread through the population, though Omicron subvariants currently make up 99.9% of all cases.

Countries and health agencies around the world have now established genomic surveillance to track novel concerning variants. Strong surveillance is key to responding to new pandemic twists and turns, according to Jarbas Barbosa, director of the Pan American Health Organization, which coordinates a regional genomic surveillance network in the Americas. The challenge is to maintain interest in these efforts even as the acute phase of the pandemic recedes.

“As we learn to live with this virus, countries must … maintain and continue to strengthen surveillance,” Barbosa said a media briefing on March 9. “The risk of new variants is real.”

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