An epidemic of viral pink eye, or conjunctivitis, is plaguing hundreds of thousands in Vietnam, India, and Pakistan.

For months amid summer heatwaves and record rainfall, the contagion has been building, as health officials in several nations struggle to curb a highly contagious pathogen that seems to thrive in high humidity.

By September, tens of thousands of schools in Vietnam, India, and Pakistan were briefly closed in an emergency attempt to stop the virus in its tracks.

In a single September day in Punjab, health officials in India tallied 13,000 new cases of pink eye. In that whole month, the city recorded more than 86,000 cases.

"At least five to six affected students were present in every class of the school," said the Caretaker Chief Minister of Punjab, Mohsin Naqvi, in a recorded statement.

In Pakistan, the number of afflicted has reached nearly 400,000 nationwide.

Officials in Vietnam say they recorded over 63,000 cases of viral conjunctivitis from January to September – an increase of over 15 percent from the same period the year before.

While pink eye can be caused by bacteria or viruses, the virus version is especially contagious. Some can live on surfaces for 30 days, spreading easily after just one fleeting rub of the eye with a contaminated hand.

"Many different types of viruses can cause viral conjunctivitis (including the COVID-19 virus)," Isabelle Jalbert, an optometrist and vision scientist at the University of New South Wales in Australia told Newsweek.

"However, the majority, up to 75 percent, of infectious conjunctivitis are caused by adenovirus. It appears that the outbreak in Pakistan involves a highly contagious form of the virus."

Patients with conjunctivitis usually present with either one or two afflicted eyes. Symptoms include redness, eye pain, swollen eyelids, blurred vision, sensitivity to light, and watery discharge.

Apart from repeated hand washing and disinfection of surfaces, there is little else that can be done to prevent the virus' spread.

There is no cure for pink eye, which means patients must simply wait it out for two weeks or more until their immune system fights off the virus. Staying at home during this time is essential to avoid wider community spread.

In the most severe cases, the eye's cornea can become chronically inflamed, leading to longer-term vision problems.

While these cases are rare, in Vietnam, hospital officials say that 20 percent of the cases they have seen in children involve severe complications.

Recurrent conjunctivitis epidemics are experienced worldwide, but because this illness tends to follow a seasonal cycle, it's possible that future outbreaks will be susceptible to climate changes, although research in this area is notably lacking.

Today, only a few studies have found that elevated temperatures are a risk factor for cases of local conjunctivitis.

In 2023, research in China found that elevated humidity increases the risk of conjunctivitis outpatient visits, although low relative humidity compared to temperature can also increase risk by causing dryness and irritation.

Air pollution likely plays a role, too.

In a rapidly changing world, it's more important than ever that governments prepare themselves for viral outbreaks of conjunctivitis.

Educating the public on what symptoms to look out for and how to isolate will be vital going forward.

Following a 2022 outbreak of conjunctivitis in India amid heavy monsoons, experts wrote a letter to the Indian Journal of Ophthalmology calling for improved disease awareness and extensive telephone-based healthcare services to assist rural and remote communities.

"It is imperative to remember that the laxity of the government, health authorities, and lack of awareness among the general public during the "preventable" conjunctivitis outbreak not only impacts the well-being of the patients and their caretakers but also poses a high socio-economic burden and prevents accomplishing universal health coverage," the authors write.

A few months after the letter was published, India's next pink eye epidemic began.