These days, if you walk past a pharmacy, you'll see banners for flu vaccines. However, this year, there's an additional question: "There's an mRNA flu vaccine out now; is it safe to get?"

The mRNA technology we heard about during COVID has now arrived for the flu. The name is Emflusiva, and it's a vaccine that Moderna has been clinically testing under the development name mRNA-1010 for a long time.

The FDA approved this vaccine for adults aged 50 and older in August of this year. It's the first mRNA-based flu vaccine approved in the United States. Considering that most existing flu vaccines are made by growing the virus in eggs or cells, this is quite a significant change.

However, if you look closely at the approval details, the specifics vary by age group. This is a key point that can be easily missed if you only read the news headlines.

For those aged 50 to 64, it has full approval. This is based on efficacy data showing how well it actually prevents the flu, making it the most solid evidence level.

For those aged 65 and older, it has accelerated approval. This means the approval was granted based on observing immune responses, specifically how many antibodies are produced.

Therefore, Moderna plans to conduct post-marketing studies to confirm the actual effectiveness in those aged 65 and older. Depending on the results, the approval for this age group may change.

Let's look at some numbers. The key Phase 3 clinical trial involved 40,805 adults aged 50 and older across 11 countries.

The comparison was not against a placebo but against the existing standard-dose flu vaccine. The study was designed to ask, "Is it better than the existing vaccine?" so it was essentially a head-to-head comparison.

The results showed that the incidence rate of flu-like illness confirmed by testing was 2.0% for Emflusiva and 2.8% for the standard-dose vaccine. When converted to relative efficacy, this is 26.6%.

There's a point here that can be easily misunderstood. The 26.6% does not mean "it prevents the flu by 26.6%"; rather, it indicates the additional reduction in incidence compared to the group that received the existing vaccine.

Honestly, I was quite surprised by this number. It's not common to see such a difference when directly comparing existing products in the flu vaccine field.

There is separate evidence for those aged 65 and older. This is based on a clinical trial comparing high-dose flu vaccines and immune responses involving 2,992 participants in the U.S. However, this data does not count actual flu cases.

So, for those aged 65 and older, there is already an option for a high-dose vaccine, and Emflusiva is still in the process of accumulating efficacy data.

We should also address side effects. Common ones include pain at the injection site, fatigue, headache, muscle pain, joint pain, chills, and swelling in the armpit on the injected side.

In the clinical trials, most reactions were mild to moderate, with a median duration of about 2 days. However, adverse reactions, including grade 3 reactions, were reported more frequently than with the comparison vaccine.

If you had a day of feeling unwell after getting the COVID vaccine, it's realistic to expect a similar experience. It's best to avoid important meetings or long drives the next day.

The approval process was not smooth either. The FDA initially rejected the review but changed its stance about a week later.

After that, in June, the FDA advisory committee (VRBPAC) unanimously supported this vaccine. The uncertainty of the regulatory environment was a bigger variable than the data itself.

The real issue is insurance. Currently, there is no recommendation from the CDC Advisory Committee on Immunization Practices (ACIP) for this vaccine.

This is because the legal disputes surrounding the ACIP vote have not been resolved. Without a recommendation, private insurers are not obligated to cover it for free.

Medicare Part B covers flu vaccines by law. However, those with private insurance or Medicaid may be charged separately for this product. This means that while existing flu vaccines are free, this one could potentially incur a cost.

In early September, Washington State recommended flu vaccines for everyone aged 6 months and older through the West Coast Health Alliance (WCHA). The message emphasizes the importance of "getting vaccinated" rather than the type of vaccine.

Supply is still limited. Not all vaccination sites have Emflusiva available, so it's a good idea to check stock by calling ahead or using a pharmacy app. Moderna also believes that this season's revenue contribution will not be significant.

In summary, for those aged 50 to 64, the efficacy data is the strongest, so if insurance issues are resolved, it's definitely worth considering.

For those aged 65 and older, there is still insufficient comparative data to determine whether the high-dose vaccine or Emflusiva is better. There's no rush.

In either case, individual underlying conditions and past vaccine reactions vary from person to person, so be sure to consult with a doctor or pharmacist. It's also wise to check with your insurance company about coverage before getting vaccinated.

Personally, I find it unfortunate that this new technology is caught in a political struggle, leaving it in an insurance gap. If good data emerges, the public system should quickly follow suit.

If I were to advise the elderly around me, I would suggest they get the vaccine that is currently available right away. The worst choice would be to hesitate and miss out on this season altogether.