Long lines for COVID-19 vaccines have become commonplace in the U.S. Michael M. Santiago/Getty Images
  • Though the coronavirus vaccinesTrusted Source and flu shotsTrusted Source use distinctly different technologies against two unique viruses, they still have the same job of teaching our immune system how to recognize and attack a virus.
  • The COVID-19 shots appear to be even more effective at preventing severe disease, along with hospitalization and death.
  • Experts suspect the vaccine technologies developed during the pandemic will be used to improve existing vaccines such as the flu shot.

As of Feb. 8, more than 42 millionTrusted Source doses of the Pfizer and Moderna COVID-19 vaccines have been administered in the United States.

The shots are safe, highly effective, and in most cases, cause mild reactions similar to the flu shot.

But, comparing the coronavirus vaccines to the flu shot is like comparing apples to oranges.

For one, the technologies used in the flu and coronavirus shots are significantly different. The viruses also have different attack rates and behavioral patterns.

And though both viruses mutate, the flu virus does so much more frequently, making it difficult to design and distribute a shot that can work perfectly against the leading flu strains each year.

Even so, both sets of shots are proficient at preventing severe illness and death.

Here’s how the COVID-19 shots stack up against the flu shot:

The shots are very different but have the same goal

Though the coronavirus vaccinesTrusted Source and flu shotsTrusted Source use distinctly different technologies against two unique viruses, they still, on a basic level, have the same job.

The shots “provide an opportunity for the immune response to recognize a foreign protein or antigen,” explained Litjen Tan, PhD, the chief strategy officer of the Immunization Action Coalition.

These vaccines’ goal is to give the immune system a way to recognize a foreign pathogen and develop a memory response. If and when the body is exposed to the virus, the immune response can be activated faster.

This quick activation of the immune system can either prevent illness or reduce the severity of the disease to varying degrees.

“How you give the opportunity to the immune response to look at this foreign antigen varies [with each type of vaccine],” Tan said.

The side effects seem to be more intense with COVID-19 vaccines

New data on the Moderna and Pfizer novel coronavirus shots show that most people experience mild reactions after being vaccinated, particularly after the second dose.

These reactions commonly include pain at the injection site and fatigue, headache, myalgia, and chills.

The flu shot is also known to trigger similar side effects — sore arm, a low-grade fever, headache, fatigue, and muscle aches.

According to Tan, the reactions are the same, but the effects reported after the coronavirus vaccines seem more intense.

“The side effects from COVID-19 vaccines are a little bit stronger. It’s a more reactive vaccine than flu vaccine,” he said.

In both cases, the side effects are a result of the immune system revving up and learning how to fight an infection.

How effective the shots are at preventing disease

The flu shots’ effectiveness fluctuates every year depending on how precisely the shots match the circulating strains, but health experts estimate it ranges from 40 to 60 percent, depending on the season.

Tan says researchers don’t conduct clinical trials on the flu shots anymore, so any recent evidence on the flu shot’s efficacy comes from looking at flu activity trends in the population.

That data suggests that “influenza vaccine not only prevents 40 to 60 against primary disease, but it’s also around that same level in terms of preventing hospitalization and severe illness in both kids and adults,” Tan said.

study published in Pediatrics in 2017 found that the flu vaccine cuts the risk of death in healthy children by about two-thirds, or 65 percent.

And according to the Centers for Disease Control and Prevention (CDC)Trusted Source, a person hospitalized with influenza is 2 to 5 timesTrusted Source more likely to die if they’re unvaccinated.

Even when the flu vaccine isn’t a strong match against the circulating strains, it still confers some degree of protection.

“The greatest benefit is probably reducing the likelihood of someone getting severe influenza, reducing duration of flu symptoms, and limiting spread to others,” said Dr. David Hirschwerk, an attending infectious diseases physician at Northwell Health in Manhasset, New York.

The coronavirus vaccines range from about 66 to 95 percent effective at preventing symptomatic disease. All of the vaccines appear to be 100 percent effective at protecting people against hospitalization and death.

“The COVID vaccines, so far, have turned out to be more effective than the flu vaccine, not only in actually preventing COVID but notably in limiting cases of severe COVID,” Hirschwerk said.

Emerging evidence suggests efficacy may wane against certain variants.

“We already know that the variant from the UK is a bit less responsive to the vaccine, but it remains very likely that severe COVID can still be mitigated by the current vaccines and even if not perfect, that would remain a substantial victory for public health,” Hirschwerk said.

Many of the vaccine developers are already working on booster shots that specifically target emerging variants.

The ease with which the shots can be modified is one of the key benefits of the new technologies used in the COVID-19 vaccines.

Modifying vaccines is much harder with the traditional technologies used.

“It’s very hard to react and make changes to variations. We struggle with it every year with flu,” Tan said.

What about preventing transmission?

According to Tan, scientists evaluate a vaccine’s ability to prevent transmission by looking at the amount of virus in people who’ve been vaccinated.

“The general feeling with flu vaccine is that it does prevent transmission,” Tan said.

That said, even though it’s thought the flu shot can significantly reduce disease transmission, vaccinated people can still contact influenza and spread it to others.

There’s limited data looking at the new coronavirus vaccines’ ability to reduce transmission of COVID-19. One small study from AstraZeneca suggests it may cut the spread by up to 67 percent.

When looking at these vaccines’ ability to curb disease transmission, it’s important to understand that the flu and new coronavirus have different attack rates, Tan says.

COVID-19 has very high attack rates. There are a lot of people who are susceptible because there’s little natural immunity in the population. Also, there’s no widespread vaccination against COVID-19, and there are no antivirals.

With flu, we can reduce transmission with vaccination because there’s a lot of pre-existing immunity in the population. We also have effective influenza antivirals that can lessen the severity of illness, Tan says.

“A lot of people have been exposed to actual flu in the past or have been multiply vaccinated, and every time we vaccinate, we boost [immunity],” he said.

The attack rate of flu compared to COVID-19 is much lower. “The bar is very different,” Tan said..

Could the COVID-19 vaccines change how we vaccinate for the flu?

Tan thinks the vaccination advancements we’ve made during the pandemic will be used to create new vaccines against many other conditions.

The technology could help make existing vaccines, like the flu shot, even better.

“I’m really optimistic that we’re going to see some genuine improvements in flu vaccine as a result of our COVID-19 technology,” Tan said.

The bottom line 

Though the coronavirus vaccines and flu shots use distinctly different technologies against two unique viruses, they still, on a basic level, have the same job of teaching our immune system how to recognize and attack a virus. Both sets of shots trigger side effects that include fatigue, chills, and in some cases, a low grade fever. The COVID-19 shots appear to be even more effective at preventing severe disease, along with hospitalization and death. Health experts suspect the vaccine technologies developed during the pandemic will be used to improve existing vaccines such as the flu shot.