The delta variant and your eyes: What we know

  • As of August 10, 2021, the delta variant had been detected in 142 countries worldwide.

  • As of late July 2021, nearly all COVID-19 cases in the U.K. and the U.S. were caused by a new strain of the coronavirus known as the delta variant.

  • Like other variants of the coronavirus, delta may be able to cause certain eye-related symptoms, but we don't know for sure yet.

  • Vaccines are less effective against delta, but they're still your best form of protection.

  • An eye test may soon be able to help detect cases of long-haul COVID.

The current spike in COVID infections could be the second-worst — or worst — upturn since the start of the pandemic. It comes at the hands of the delta variant, which spreads as easily as chickenpox among people who are unprotected.

Delta cases were first documented in India in October 2020 before being spotted in the U.K. and U.S. in February 2021. Globally, 142 countries had cases of the delta variant by August 10. Of those, delta accounted for over half of all COVID-19 cases in approximately 45 countries and over 80% of cases in 37 countries.  

The CDC estimates more than 97% of new COVID cases in America are currently caused by delta infections, as of August 7. About 83% of total cases are caused by the original delta variant, while 14% are caused by a handful of subtypes known as delta plus

There were early concerns about delta plus overtaking the original delta strain. But as the rate of delta plus infections level off, delta plus may not be any more of a threat than delta itself.

The three most widely available COVID-19 vaccines — Pfizer, Moderna and Johnson & Johnson — will still protect you against the delta variant, but not as effectively as they did against previous strains. Fortunately, these "breakthrough cases" appear to be much less common and more mild, on average.

Can the delta variant cause eye symptoms?

We don't know for sure — yet. Previous strains of COVID could cause eye-related symptoms, but there isn't enough scientific data available right now to say with certainty that delta does the same.

Although not nearly as common as symptoms like cough and fever, other strains of the coronavirus were capable of causing:

It isn't a stretch to think that some delta infections are capable of causing similar eye symptoms, but, like other aspects of delta, we need to wait for more information.

While each infection is different, delta seems to be causing slightly different symptoms overall than earlier forms of COVID.

"It seems like cough and loss of smell are less common," said Dr. Inci Yildirim, a  pediatric infectious disease specialist at Yale Medicine, in an article about the delta variant. "And headache, sore throat, runny nose and fever are present based on the most recent surveys in the U.K., where more than 90% of the cases are due to the Delta strain."

If a set of symptoms that includes runny nose, sore throat and headache sounds familiar, it's because many delta infection symptoms resemble a bad case of seasonal allergies.

This is where eye-related symptoms could get even more confusing.

If you have bad seasonal allergies, you probably know how much allergies can affect your eyes. Red, bloodshot eyes are a hallmark symptom; itchiness, watering and even blurry vision are also common.

And while "classic" COVID symptoms are becoming less common, they can still show up. Cough, loss of taste or smell, and certain gastrointestinal symptoms still occur, but they're becoming less likely.

MIS-C: A rare but growing concern in children

As delta finds ways to infect more young people than earlier strains, a rare but serious complication of COVID is also expected to be on the rise.

MIS-Cmultisystem inflammatory syndrome in children — can cause vital organs and other parts of the body to become inflamed. It shares similarities with Kawasaki disease, a condition uncovered earlier in the pandemic.

We don't currently know why MIS-C happens to some children.

Symptoms of MIS-C can vary. It can also cause red, bloodshot eyes, but like COVID-19, it's unlikely that would be the only symptom. Additional symptoms occur alongside a fever, according to the CDC.

In addition to a fever, MIS-C symptoms can include:

  • Bloodshot eyes

  • Headache

  • Abdominal pain

  • Chest pain or tightness

  • Diarrhea

  • Fatigue

  • Neck pain

  • Low blood pressure

  • Rash

  • Vomiting

As of July 31, there have been 4,400 verified cases of MIS-C, with others under investigation. Thirty-seven children have died from the complication.

While rare, the CDC recommends seeking emergency care if you notice symptoms such as difficulty breathing, chest pain or pressure, pale skin or any other severe symptoms.

The eyes could offer insight into long COVID cases

There's a lot we still don't know about long COVID, the symptoms that linger for weeks or months after the initial infection clears up. Sometimes, symptoms seem to continue indefinitely, significantly impacting a person’s quality of life.

Also known as "long-haul COVID" or "post-acute COVID," long COVID can show up as one or more of a multitude of symptoms. In addition to many others, ongoing symptoms can include:

  • Fatigue

  • Changes in taste or smell

  • Difficulty breathing

  • Brain fog

  • Cough

  • Chest pain

  • Joint pain

  • Heart palpitations

  • Worsening symptoms after physical activity

We don't yet know how often long COVID occurs after a delta infection, or among vaccinated people. One February study found that roughly 30% of people were still experiencing symptoms between three and nine months after having COVID.

About one in 12 participants reported that symptoms affected their ability to complete at least one "activity of daily living," with household chores being the most common.

Long COVID is a developing issue that will continue to affect millions of people for the foreseeable future. Standardized treatment options may not be available yet, but clues to diagnosis could lie in — of all places — the eyes.

Corneal nerve fibers in a healthy person (A), a COVID-19 patient without long COVID (B) and one with long COVID (C). [Image courtesy: British Journal of Ophthalmology]

There may be a connection between long COVID and damage to microscopic nerve fibers in the cornea, the clear layer in front of the pupil, according to a study published in July.

Ophthalmologists used a painless, noninvasive test called a corneal confocal microscopy, a procedure used to diagnose several other conditions that affect the cornea.

While the study acknowledged that more research is needed, the discovery could eventually be a stepping stone toward recovery for people affected by ongoing symptoms, especially neurological.

Getting help from a medical professional

COVID-19's symptoms can be unpredictable, and, like other illnesses, it's important not to self-diagnose. People who experience symptoms are advised to follow the latest guidance from the World Health Organization (WHO) and from the NHC.

If you think that you or someone you know has COVID-19 or long-haul COVID, speak with a medical professional.

If you notice emergency symptoms such as difficulty breathing, chest pain or pressure, confusion or skin discoloration, seek medical attention as soon as possible.

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Expert reaction to cases of variant B.1.617 (the ‘Indian variant’) being investigated in the UK. Science Media Centre. April 2021.

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Tracking of variants. GISAID. Accessed August 2021.

CDC COVID data tracker. Centers for Disease Control and Prevention. August 2021.

Coronavirus pandemic (COVID-19): Which vaccines have been administered in each country? Our World in Data. August 2021.

About variants of the virus that causes COVID-19​​. Centers for Disease Control and Prevention. August 2021.

Sore eyes as the most significant ocular symptom experienced by people with COVID-19. BMJ Open Ophthalmology. November 2020.

5 things to know about the delta variant. Yale Medicine. August 2021.

Symptoms of the delta variant vs. previous COVID-19 strains. Baton Rouge General. July 2021.

Is It COVID-19 or allergies? American Academy of Ophthalmology. January 2021.

When you’ve been fully vaccinated. Centers for Disease Control and Prevention. Accessed 6 August 2021.

Health department-reported cases of multisystem inflammatory syndrome in children (MIS-C) in the United States. Centers for Disease Control and Prevention. Accessed 16 August 2021.

For parents: Multisystem inflammatory syndrome in children (MIS-C) associated with COVID-19. Centers for Disease Control and Prevention. Accessed 16 August 2021.

MIS-C and COVID-19: Rare inflammatory syndrome in kids and teens. Johns Hopkins Medicine. July 2021.

Post-COVID conditions. Centers for Disease Control and Prevention. Accessed 6 August 2021.

Sequelae in adults at 6 months after COVID-19 infection. JAMA Network Open. February 2021.

A pandemic that endures for COVID long-haulers. The Harvard Gazette. April 2021.

Corneal confocal microscopy identifies corneal nerve fibre loss and increased dendritic cells in patients with long COVID. British Journal of Ophthalmology. July 2021.

Clinical applications of corneal confocal microscopy. Clinical Ophthalmology. June 2008.

Coronavirus. Prevention. World Health Organization. Accessed August 2021.

Symptoms of COVID-19. Centers for Disease Control and Prevention. Accessed 6 August 2021.

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