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Illustration: Eniola Odetunde/Axios

How sick a person gets from a virus can depend on how much of the pathogen that person was exposed to and how much virus is replicating in their body — questions that are still open for the novel coronavirus.

Why it matters: As people try to balance resuming parts of their daily lives with controlling their risk of COVID-19, understanding the role of viral load could help tailor public health measures and patient care.

Driving the news: An analysis of 5,000 genomic sequences of the coronavirus from patients found those infected with a now-dominant strain with a specific mutation "had higher loads of virus in their upper respiratory tracts, a potential factor in making the strain spread more effectively," the Washington Post reports.

  • Viruses typically mutate as they spread through a population, and the mutation that is accumulating wasn't linked to the virus becoming deadlier, according to the study, which hasn't yet been peer-reviewed.
  • But the research underscores open questions about COVID-19: How does the amount of virus in someone affect transmission to others, and the severity of the disease?

How it works: Viral dose is how much virus someone is exposed to when they are infected. Viral load is the amount of virus produced in someone's body after they are infected.

  • A higher infectious dose of a virus and a higher viral load are linked to more severe disease from influenza, poxviruses and other viruses.

For SARS-CoV-2, the virus that causes COVID-19, "there's accumulating data on both sides of the equation," Monica Gandhi, a professor of medicine and an infectious disease doctor at UCSF, tells Axios.

  • In a study of Syrian hamsters, for example, those infected with a higher dose of SARS-CoV-2 had worse outcomes than those with smaller amounts, supporting an earlier study on hamsters checking if "masks" helped prevent transmission, she points out.
  • Outbreak investigations show that where there's universal masking of a population, the severity of disease goes down.
  • Some researchers suggest a decline in death rate and the rise in asymptomatic cases in the U.S. this summer — both coming at a time when mask-wearing became more common — indicate reducing the dose of the virus may reduce the severity of disease.

"It's very interesting that it seems like it's correlating with masking, this lower rate of severe illness," says Gandhi, adding that the hypothesis remains unproven but has some growing evidence behind it.

  • She co-authored a perspective piece in the NEJM this week that says universal adoption of masks could reduce infections and severity until an effective vaccine is distributed.
  • Last week, CDC director Robert Redfield suggested face masks are "more guaranteed" to offer protection against the coronavirus than a potential vaccine.

What's happening: Evidence is emerging about the link between viral load and how severe COVID-19 is for a patient.

  • In a study of more than 3,000 patients in three New York City hospitals, nearly 40% who tested positive for COVID-19 and had a high viral load died in the hospital.
  • But the risk of dying was lower — dropping to about 15% — for patients with a low viral load, Michael Satlin, an infectious disease specialist at Weill Cornell Medicine and NewYork-Presbyterian, and colleagues reported last week in the journal Cancer Cell.
  • Of note: The study was done at the height of the city's outbreak in the spring, and Satlin says that given improvements in caring for patients with COVID-19, he wouldn't expect to see such high mortality rates today.
  • And the amount of virus the patients were exposed to or their viral load when symptoms started wasn't known — connecting those dots will require more testing, he adds.

Yes, but: Other studies have also found some people without symptoms can have viral loads similar to those with symptoms. And children, who tend to be spared severe COVID-19 complications, can carry as much or more of the virus in their upper respiratory tract.

  • "Viral load is a part of the picture, but it's not the full picture," infectious disease specialist Ravina Kullar told MedPage Today, adding that disease severity depends on a person's immune system.

What to watch: Knowing a patient's viral load could be helpful to providers in determining how therapies should be directed.

  • Viral load information is in the PCR tests done to confirm SARS-CoV-2 infection but the tests aren't approved by the FDA for that quantitative information, Satlin says.
  • If it could be released to clinicians, "it could be very useful" for determining care for people who are hospitalized, he adds.

Go deeper: Where the science stands on using face masks against coronavirus

Go deeper

Updated 5 hours ago - Politics & Policy

Omicron dashboard

Illustration: Shoshana Gordon/Axios

  1. Health: Contact tracing fizzles across America — New clues emerge on long COVID — Omicron is finally burning out — It's very difficult to get access to antiviral COVID treatments — Axios-Ipsos poll: Omicron's big numbersAnother wave of death — FDA limits use of Regeneron and Lilly antibody treatments.
  2. Vaccines: Pfizer begins clinical trial for Omicron-specific vaccine — The shifting definition of fully vaccinated.
  3. Politics: Virginia AG says public colleges can't mandate COVID vaccines —Alaska governor joins Texas lawsuit over National Guard vaccine mandate — Navy discharges 45 sailors for refusing vaccine — Spotify to remove Neil Young's music after his Joe Rogan ultimatum.
  4. World: U.K. to lift travel testing requirement for fully vaccinated — Beijing Olympic Committee lowers testing threshold ahead of Games.
  5. Variant tracker
Updated 15 mins ago - Energy & Environment

Bomb cyclone prompts blizzard warnings from Virginia to Maine

Computer model projection showing the intense storm off of Cape Cod on Jan 29, 2022, with heavy snow and strong winds lashing the coastline. (Weatherbell.com)

Blizzard warnings are in effect for 11 million people from coastal Virginia to eastern Maine as a potentially historic winter storm is set to slam the Mid-Atlantic and Northeast beginning Friday.

Why it matters: The storm will bring hazards ranging from zero visibility amid hurricane force wind gusts and heavy snow, to coastal flooding that will erode vulnerable beaches and threaten property from the Jersey shore to coastal Massachusetts.

Updated 4 hours ago - Politics & Policy

Swastikas found outside Union Station in D.C.

People walk through Union Station on Jan. 16 in Washington, D.C. Photo: Spencer Platt/Getty Images

Drawings of swastikas appeared etched around the entrance to Union Station in Washington, D.C., on Friday morning.

Driving the news: "An investigation is underway with Amtrak Police and the Metropolitan Police Department after swastikas were reported on the exterior of Washington Union Station on Friday," Amtrak spokesperson Kimberly Woods said in a statement to Axios.