Why COVID-19 Still Surges in Summer, and What to Watch For

COVID-19 is often associated with winter, but infection rates can peak higher during the summer months, according to Gurinder S. Sidhu, M.D., senior medical director and U.S. antiviral medical lead at Pfizer. Closed indoor environments, increased travel and unexpected symptoms that mimic jet lag or a summer cold can all make it easier for the virus to spread undetected. Sidhu breaks down what symptoms to watch for, and why people don't always realize they've contracted COVID-19 when it doesn't fit the winter-illness expectation.

Sidhu also discusses how COVID-19 can interact with and worsen existing chronic conditions like diabetes, heart disease and asthma, and why the virus's potential to trigger new health issues, from heart problems to kidney complications, makes early action especially important. He explains why waiting to see if symptoms worsen can be risky, and what patients at high risk should know about prescription treatment options and their narrow treatment window.

COVID-19 is often thought of as a winter illness. Why does it also tend to surge in the summer, and what symptoms should people be watching for right now?

Gurinder S. Sidhu, M.D.: Many people are surprised to learn that COVID-19 not only spreads in the winter but can surface in the summer months as well. In fact, infection rates can peak higher in summer months compared with winter.

Closed environments and summer travel allow a virus like COVID-19 to circulate and lead to greater spread and risk of getting sick with the virus, even during warmer months. Warmer temperatures and increasing humidity may lead people to seek relief indoors with the air conditioning on and windows shut much of the time. Additionally, many people also travel more during the summer, where they're exposed to more people.

Because they aren't expecting it, it's easy for people to mistake mild symptoms, such as tiredness, headache or sore throat, for jet lag or simply something else, when they may have actually picked up COVID-19.

The start and end times of when infection rates rise and fall can also vary each year.

Common COVID-19 symptoms include fever, cough, sore throat and loss of taste and smell. But COVID-19 can also cause fatigue, nausea or vomiting, and even diarrhea. The Centers for Disease Control and Prevention also has a full list of potential COVID-19 symptoms on their website.

For someone with an underlying condition like diabetes, heart disease or asthma, how does a COVID-19 infection interact with and potentially worsen what they're already managing?

GS: This is an interesting question. We are seeing a growing body of evidence reinforcing the notion that COVID-19 has the ability to make preexisting medical conditions worse. And, even when an underlying medical condition is being properly managed by the patient, COVID-19 can still lead to serious outcomes.

The Mayo Clinic notes that these underlying medical conditions become more common as people age, but they can affect people of any age. The risk of serious COVID-19 illness is also linked to having one or more underlying medical conditions.

Why is this the case? Well, one explanation is that living with a (or multiple) chronic condition causes the immune system to be less capable of responding to infections, which makes it harder for the body to recover and raises the likelihood of developing serious illness.

I would recommend that anyone at high risk of severe COVID-19 seek care as soon as possible rather than waiting to see whether symptoms get worse, as that can happen very quickly.

That statistic about 1 in 3 adults over 65 developing a new health condition after COVID-19 is striking. Can you walk us through what's happening physiologically that leads to something like heart failure or new-onset diabetes after infection?

GS: Many people may not be aware that it is possible to develop new health issues as a result of an acute COVID-19 infection.

COVID-19 is often thought of as an illness that mainly affects the respiratory system, but what a lot of people don’t know is that it can impact multiple parts of the body. For example, it can lead to heart problems, scarring in the lungs or kidney failure.

In some people with COVID-19, the immune system remains active longer than expected, which can lead to ongoing inflammation that affects different parts of the body. COVID-19 can place stress on organs (such as the heart or lungs) or some of our body systems (such as our circulatory or nervous systems), especially after more severe illness; this added stress could lead to long-term health problems.

Why do you think COVID-19 gets overlooked during the summer months, and what does "early action" look like for someone who starts feeling symptoms?

GS: During summer, many Americans do not expect to get sick with COVID-19 and are unaware of the fact that the virus does spread — sometimes, at levels higher than in winter months — when the weather warms up.

As such, people may think their symptoms are due to things like jet lag or a “summer cold” and continue their daily activities. This can cause them to try to “push through it,” resulting in their symptoms getting progressively worse or unintentionally spreading the virus to others.

That’s why early action is key here. As first steps, I might recommend testing for COVID-19 and reaching out to a doctor ASAP as soon as someone starts to feel sick.

Prescription treatment options exist for COVID-19, but many patients don't bring it up with their doctor. Who's a good candidate for treatment, and what would you want patients to know before that conversation?

GS: For people who are at high risk for progression to severe COVID-19, it is important to seek care as soon as they experience symptoms or test positive for the virus, rather than waiting to see whether they start feeling worse.

While over-the-counter medications may help people feel better in the short term by easing symptoms like congestion or reducing pain like body aches or a sore throat, prescription medication exists to help treat the virus itself and help stop it from multiplying.

Because prescription medications must be started within five to seven days from the start of symptoms, it’s important to be in touch with a doctor as soon as someone starts to feel sick. Together, they can decide on the care plan that works best for the patient.

If someone doesn’t have a regular doctor, there are other options available for care, such as a local urgent care center or telehealth. Whatever option they choose, I recommend ensuring people speak with a reputable, licensed clinician.

This discussion guide might also help jump-start conversations with the provider.