As cold and flu season ramps up, health care experts are once again on high alert for the possibility of a tripledemic, or a surge brought on by the respiratory viruses that cause COVID-19, the flu and respiratory syncytial virus, or RSV. The good news is that this year, health officials have more tools at their disposal to combat them.

Americans ages 6 months and older are eligible to receive the newest COVID-19 vaccine and the annual flu vaccine. In addition, this year the Food and Drug Administration approved the first vaccine against RSV for use in late pregnancy and adults 60 years of age and older.

RSV, COVID-19 and the flu are all contagious respiratory illnesses that have similar symptoms, making it difficult to distinguish between the three viral infections without a lab test. Testing is the only way to know which virus is causing your symptoms. In fact, researchers are working to create one test that can detect COVID-19, RSV and the flu.

As a nursing professor with experience in public health promotion, I am often asked about the differences between these respiratory viruses. This year, I am fielding many questions about the timing of getting the new COVID-19 and RSV vaccines along with the flu shot, and whether they can be given together.

What to know about the symptoms

Symptoms of COVID-19, RSV and the flu can range from mild – or even no noticeable symptoms at all – to severe. Flu symptoms typically come on suddenly, while RSV and COVID-19 often start out mild but can become severe over time. In addition, while a flu infection does not typically affect one’s ability to taste or smell, the loss of taste or smell can be a common COVID-19 symptom.

All three infections can cause fevers and fatigue, while chills and body aches are more common with COVID-19 and the flu. More severe symptoms of these infections include difficulty breathing and subsequent infections like pneumonia.

Timing the shots

With the new RSV vaccine and updated COVID-19 vaccine now available and flu season just around the corner, a natural question is whether there is an optimal schedule for the three shots.

The answer to that question is, if you are eligible, to get these vaccines as soon as possible. It is important to consider that it takes approximately two weeks after vaccination for your body to develop antibodies from both the COVID-19 vaccines and the flu vaccine.

The Centers for Disease Control and Prevention recommends that anyone who is either unvaccinated or has previously received a COVID-19 vaccine before Sept. 12, 2023, to get the updated vaccine. This means now is the time to get the updated COVID-19 vaccine that targets a previously dominant variant of the omicron family.

The original COVID-19 vaccines and booster series have dramatically reduced the number of COVID-19 infections, hospitalizations and death rates from the virus.

While everyone 6 months of age and older is advised to receive both the COVID-19 and flu vaccines, certain populations have a higher risk for severe infection, such as pregnant women, and should be extra vigilant about getting vaccinated.

In addition, among those vaccinated against COVID-19, symptoms during an infection tend to be milder. However, due in part to the quickly evolving nature of the virus, it has become clear that immune protection from COVID-19 vaccination or infection diminishes over time. While studies show that the primary COVID-19 series maintains efficacy against severe disease and death six months after vaccination, protection after vaccination decreases over time. Viruses, such as those that cause COVID-19 and influenza, also continuously mutate and evolve.

The fact that COVID-19 vaccine immunity decreases over time and that viruses evolve are exactly why updated vaccines are so critical. Without a large uptake of updated vaccines in the population, COVID-19 infection rates could surge again.

Timing is also important with the flu vaccine. Flu cases typically begin to rise in October and peak between December and February, but can last through May. Ideally, people should get vaccinated before flu begins to spread, making the month of October the ideal flu vaccination time.

But if you miss that deadline, it is absolutely better to get vaccinated later in the season than not at all. Flu, COVID-19 and RSV vaccines are available at your health care provider’s office, your local health department and most retail pharmacies, although access to the newly updated COVID-19 vaccine is still limited in some areas of the country.

A difficult respiratory virus season ahead

While infections and hospitalizations from COVID-19 declined dramatically in 2023, experts are remaining vigilant against the possibility of new, more-infectious variants causing another fall and winter surge. Adults 65 and older continue to be the highest-risk group for severe infection.

Flu seasons are inherently difficult to predict. Since the emergence of the COVID-19 pandemic, flu cases have been lower than prior to the pandemic. However, the 2022-2023 flu season still caused over 300,000 hospitalizations and up to 98,000 flu-releated deaths, making vaccination an important prevention tool.

To further compound this, flu vaccine rates have been lower during the pandemic, suggesting that Americans may be out of the habit of getting their annual flu shot.

Shots can be given together

Many are also wondering whether they can or should get the updated COVID-19 booster, the new RSV vaccine and the flu shot at the same time. The good news is, the CDC clearly indicates that it is safe for both adults and children who are eligible for the updated COVID-19 vaccine to get this vaccine simultaneously with the annual flu shot.

A 2022 study found that common vaccine side effects, such as pain at the injection site, occurred at slightly higher rates when someone received the flu vaccine and a COVID-19 vaccine at the same time, as opposed to receiving only a COVID-19 booster. However, those reactions, including fatigue and headache, were mild and resolved within a day or two. In addition, a recent study found that the immune response was the same when both vaccines were given together compared to when given separately.

Since the RSV vaccine is new, there is no data yet on receiving all three vaccines at the same time. Instead, those at the highest risk of RSV infection should get this vaccine as soon as they are able.

Community matters too

Getting the COVID-19, RSV and flu vaccines isn’t just about your own health – it’s about family and community health too. Communities with higher vaccination rates have fewer opportunities to spread the virus.

Keep in mind that many people cannot be vaccinated, because they have weakened immune systems or are undergoing treatments. They depend on those around them for protection. While one person may experience mild symptoms if they contract RSV, COVID-19 or the flu, they could spread the virus to others who could become severely ill.

Because it’s impossible to predict how people will react if they get sick, getting the flu and COVID-19 vaccines – and the RSV vaccine if you are eligible – is the best prevention strategy.

This is an updated version of an article that was originally published on Sept. 22, 2022.

Libby Richards has received funding from the National Institutes of Health and the American Nurses Foundation.