Is it safe to get flu and COVID-19 vaccines at the same time?

• It is safe to have an influenza vaccine at the same time as a second dose of a COVID-19 vaccine, according to a study.
• The coadministration of the two vaccines did not affect the immune response.
• Only a few people reported mild side effects, such as fatigue or soreness at the injection site.
• The United Kingdom’s National Health System (NHS) says that the results show that people have nothing to worry about if both appointments fall on the same day.
• Having appointments for both vaccines at the same time could also lessen the administrative burden on the healthcare system.

The U.K., like many countries around the world, saw an almost nonexistent flu season last year, largely owing to lockdowns, physical distancing, and mask wearing.

However, this year, several reports suggest that we may see a rise in respiratory tract infections compared with 2020.

Some experts have also expressed fears about a “twindemic” of flu and COVID-19, which has strengthened calls for vaccination against both.

Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.

From September, the U.K. said it would offer more than 35 million people free influenza vaccines in what politicians are calling the most comprehensive flu program in the country’s history.

This year, the rollout also coincides with more people getting second doses or boosters of the COVID-19 vaccine.

This timing means that many people may have overlapping appointments for both vaccines. Some people may be worried about having them on the same day, but are such concerns valid?

The Combining Influenza and COVID-19 Vaccination (ComFluCOV) study in the U.K. investigated the coadministration of these vaccines to check whether it was safe. The Lancet has published the findings as a preprint.

Administering different flu and COVID-19 vaccines

Dr. Rajeka Lazarus, a consultant in microbiology and infectious diseases at University Hospitals Bristol and Weston NHS Foundation Trust and chief investigator for the ComFluCOV study, told Medical News Today that the team conducted the trials “to support the potential need to administer COVID-19 boosters alongside seasonal influenza vaccines”.

Researchers at the University of Bristol led the study, which involved 679 volunteers across 12 NHS sites in England and Wales. The volunteers were all over the age of 18 years and had received at least one dose of the Pfizer-BioNTech or Oxford-AstraZeneca COVID-19 vaccine.

The researchers examined six combinations involving the two COVID-19 vaccines and three flu vaccines: Flucelvax QIV, Flublok Quadrivalent (QIVr), and Fluad. A different cohort of participants tested each combination.

The researchers randomly allocated half of each cohort to received the flu vaccine or a placebo saline injection on the same day as the second dose of the COVID-19 vaccine. They administered the vaccines in opposite arms so that they could tell which injection was responsible for any local reactions.

After 3 weeks, the participants in the placebo groups received the flu vaccine.

The researchers then set up a follow-up study to discuss any side effects. They also collected blood samples from the participants.

What were the results?

The most common side effects that the participants reported were pain around the injection site and fatigue. Only one person experienced a rare reaction and was admitted to the hospital with a migraine.

Two vaccine combinations led to a slight increase in the number of people who reported at least one side effect when they received both of the vaccines together, but the reactions were mostly mild or moderate.

The researchers found no significant difference in four out of the six group combinations.

The study also found that the immune responses to both the influenza and COVID-19 vaccine were preserved with coadministration.

Moreover, 98.7% of the volunteers said that they would be willing to have two vaccines at the same time in the future.

Where the study may fall short

The study included people who were pregnant, immunocompromised, or aged 65 or over and those who had severe uncontrolled medical problems. Therefore, the participants were a good representation of the general population, as well as being the people that doctors would be most likely to recommend getting both vaccines.

However, most of the participants (more than 92%) were white, which could make the results less applicable to places such as the U.S. where the racial demographics are different, pointed out Dr. Donald Alcendor, associate professor of microbiology and immunology at the HBCU Meharry Medical College.

The small number of volunteers for the many combinations of the vaccines is also a limitation, he added, as is the assessment of only local and unsolicited systemic reactions and humoral responses.

“This is a well-designed study to assess both adverse effects and humoral responses to the flu and COVID-19 vaccines when administered separately and at the same time, as it would be beneficial in the upcoming flu season to administer both simultaneously,” said Dr. Monica Gandhi, professor of medicine and the associate chief of the Division of HIV, Infectious Diseases, and Global Medicine at the University of California, San Francisco.

However, she said that it was important to determine whether simultaneous administration decreases the immune response to either vaccine, given the importance of full protection from both infections.

In the study, the immune response to the second COVID-19 dose appeared slightly lower following the simultaneous administration of the quadrivalent influenza vaccines, but the difference is so slight that it is unlikely to be clinically relevant.

Dr. Gandhi told MNT that the biggest limitation of the study was that the team studied only humoral responses — SARS-CoV-2 IgG and hemagglutinin antibody inhibition — to assess immune responses.

She underscored that there are other immune responses that are likely more important to measure protection, including neutralizing antibody titers and T-cell immune response.

The researchers of the study collected neutralizing antibody titers from the volunteers but have not yet reported on the results. Dr. Lazarus told MNT that the current report details antibody binding and that the team will publish antibody function in a future report.

“I think we have become newly aware during the COVID-19 pandemic of the importance of cellular immunity and immune memory to assess responses to vaccinations and that antibodies are merely one aspect of the immune response. Relying on antibody titers alone does not give a full picture of the immune response,” Dr. Gandhi continued.

Dr. Alcendor said that another limitation is the short period of observation, noting that the study also gives no indication of long-term follow-up to determine the rate of antibody waning over time.

“I think it is important to look at T-cell responses in this type of study, but you would need to look at these responses over a longer duration than this study allows. Neutralizing antibody titers are essential to determine the efficacy of the coadministration of these vaccine combinations. The level of neutralizing antibodies over time will be highly significant in this study. Mucosal protection against influenza by measuring IgA is also important,” he added.

Dr. Gandhi highlighted an area of research that needs further investigation:

“Although coadministering vaccines is usually safe, we do not have a lot of data on whether simultaneous administration diminishes the immune response. One study found lower antibodies to pneumococcal antigen when the pneumococcus vaccine was simultaneously administered with the flu vaccine, but [it] also didn’t measure immune memory. So, this study adding on cellular memory assays will be helpful.”

Multiple vaccinations at once

Healthcare professionals often carry out routine vaccinations together, but few, if any, interactions are reported.

In the U.K., for example, a 2-month-old baby will receive the 6-in-1, pneumococcal (PCV), and rotavirus vaccines at the same time.

Similarly, a 2013 study found that administering the 4CMenB vaccine alongside routine vaccines increased the risk of fever and local tenderness at the injection sites but had no negative effect on the immune response.

Dr. Alcendor said that people often get combinatorial vaccinations, such as measles-mumps-rubella (MMR) and tetanus, diphtheria, and pertussis (Tdap).

“We already have instances where we get multiple vaccines on the same visit for childhood scheduled vaccinations, for military personnel, and when traveling abroad. Therefore, we have prior experience with multiple vaccines administered on the same day that provide broad protection against more than one disease or in the form of multiple vaccinations and combinatorial vaccines.”

– Dr. Donald Alcendor

The Centers for Disease Control and Prevention (CDC) say that it is fine to give the flu and COVID-19 vaccines at the same time, too. The organization points out that the reactions are similar with separate administration and coadministration.

The CDC also recommends that everyone aged 6 months or older get a flu shot.

Apart from getting two vaccines on the same day, there is also talk of combining both in one jab. Moderna recently announced that it is working on an all-in-one COVID-19 vaccine booster and flu shot.

Dr. Alcendor believes that the convenience of such a solution could convince more individuals who are accepting of both vaccines to get them.

However, he also warns that if people are opposed to one of the vaccines, they will certainly opt out of a combinatorial jab.

“Many [may] think that getting both vaccines may increase their chances of having more severe side effects. [But] the vaccine that Moderna is working on has the advantage of being mRNA vaccines for both flu and COVID-19 in the same formulation that are given together in the same shot. That advantage could encourage people to get vaccinated,” he explained.

So, should I worry if they are on the same day?

In short, no.

The study found no significant differences between receiving the jabs on the same day and getting them 3–4 weeks apart.

The timing of the jabs also had no major effect on antibody response to either vaccine.

The team presented the results of the study to the U.K. Joint Committee on Vaccination and Immunisation, ultimately shaping the country’s fall and winter plan.

The committee later issued advice saying that the coadministration of the flu vaccine with a booster or second dose of a COVID-19 vaccine is fine.

And although health bodies will not recommend that everyone should get both vaccines on the same day, both the CDC and NHS say that this approach is safe and convenient.

“It is best to get vaccinated for both of these serious respiratory infections this year than not get vaccinated at all, so go ahead and get them at the same time. You are unlikely to have worse adverse effects and should have a good reaction to both.”

– Dr. Monica Gandhi

Getting both vaccines on the same day could also have a practical benefit for healthcare administrators.

“People certainly shouldn’t worry if their appointments end up on the same day. Coadministration may be more convenient — only one trip to the GP surgery, clinic, or pharmacy as opposed to two. But apart from the convenience, and the cost to the NHS/providers, there is no medical or immunological reason to go out of your way to get the vaccines at the same time,” states the immediate past chair of the British Medical Association’s Public Health Medicine Committee, Dr. Peter English.

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