As summer winds down, several diseases are winding up, like Covid-19 infections and rare mosquito-borne illnesses. Unfortunately, we can expect the same for vaccine-preventable diseases, according to new CDC data.

We also have some good news: the approval of a new mRNA flu vaccine. If you’re deciding whether to get it, there is some important nuance for you to consider.

Here’s your disease “weather report” and what it may mean for you and your family.

Disease weather report

Covid-19 wave is still small, but growing

Covid-19 levels (e.g., emergency department visits, wastewater transmission), remain low nationally but continue to rise in every state. The South and the West are the leaders, which is typical this time of year.

By the end of this wave, we can expect 10-15% of people to get infected. Thankfully, the number of hospitalizations isn’t nearly as high with population immunity, but Covid-19 remains serious for older adults, infants, and people who are immunocompromised.

Are Covid-19 metrics still useful for tracking waves? Yes, when used together.

It’s true that fewer people and places are testing, but the positivity rate reflects the share of tests, which helps show the direction of trends. For wastewater, the number of sites has dipped slightly (from ~1,500 to 1,300), and funding is hanging on by a thread, but our systems still cover ~144 million people.

Dengue cases creeping northward

It’s peak mosquito season. So rare mosquito-borne diseases like dengue (also known as “break-bone fever” due to severe joint pain) are popping up in the news, particularly in the Southern and Western U.S.

Last week, the first-ever non-travel-related  Dengue case was reported in Virginia. A local mosquito bit a returning traveler with dengue, then bit another person nearby, and they got sick. This isn’t going to turn into an outbreak, because these mosquitoes only feed every few days, stay within a few hundred yards of where they hatched, and live just 2-4 weeks.

A few decades ago, epidemiologists would have been surprised to find locally acquired dengue in the U.S., as it was typically confined to the equator.

Mosquitoes in the U.S. have long been capable of carrying the disease (so infected mosquitoes aren’t marching northward from the equator), but the environment in the U.S. didn’t have conditions for the disease to thrive. Now, infected travelers combined with longer, warmer seasons create the perfect conditions for transmission. Scientists expect it to become increasingly common.

Vaccination rates continue to move backward

We can expect measles, whooping cough, and other vaccine-preventable diseases to continue to creep back up, according to CDC data released yesterday.

Some takeaways:

1. Americans continue to vaccinate at high rates. The national MMR rate is 92.4%. (When was the last time that 92% of Americans agreed on something?) But all vaccines are decreasing by a tiny percent, and, in raw numbers, this means ~280,000 kindergarteners are unprotected.
2. Exemption rates are climbing fast, though how fast varies widely by state. 
3. In Idaho, for instance, one in six kindergarteners is exempt from vaccines for religious or philosophical reasons. This is compared to near-zero rates in the five states, including California and West Virginia, that don’t allow such exemptions at all.

Spotlight on the new mRNA flu vaccine: The good, the not-so-great, and open questions

By now, you’ve probably seen the headlines: FDA approved the first mRNA flu shot (called mFlusiva) for older adults. Many people are excited about it. (It is great news!) Here is the nuance to help you make an evidence-based decision this fall.

The good: We needed better flu vaccines

In a large clinical trial, the mRNA flu vaccine was more effective than a standard vaccine at preventing symptoms in adults aged 50 and older: 2% of people who got mFlusiva developed flu, compared to 2.8% who got the standard shot. This equates to a 27% more effective vaccine.

This is good news because our standard flu vaccines aren’t that great at preventing infection. The flu virus mutates quickly, so flu vaccines can range from 15% to 60% effective each year, depending on how much the virus has changed over the 6 months it takes to make the vaccine and get it into arms. Any improvement is great. In addition, mRNA vaccine formulas can be updated in weeks, which would be enormous if we can adapt the annual policy pipeline to match that speed (or in case we get a flu pandemic).

The not-so-great: More side effects

If you’re like me and the mRNA Covid-19 vaccine knocked you out for a day or two, I have some unfortunate news: this one will probably do the same. That’s because, for some people, the immune system reacts to how mRNA vaccines are delivered into your cells (via lipid nanoparticles), leading to more inflammation.

Compared with a standard flu shot, the mRNA flu vaccine causes more injection-site pain (66% vs. 30%), fatigue (45% vs. 20%), and headaches (38% vs. 18%). Most of these side effects were mild and gone within a day or two, and no serious safety issues arose.

The open questions

1. How well does it work for seniors? It’s unclear.

For adults aged 50-64, the vaccine was fully approved because the clinical trial was straightforward: fewer people got sick.

For adults 65 and older, it’s messier.

This group usually gets a high-dose flu shot, since their immune systems respond less strongly to a standard dose. But mFlusiva was never tested head-to-head against that high-dose shot in a clinical trial. Instead, it was approved for this age group based on high antibody levels tested in petri dishes. The mRNA flu vaccine has been shown to generate broader antibody responses than current vaccines, suggesting it could be more effective over time. The T cell response also seemed better. This will likely mean they are better, but we don’t have enough data yet to confirm this or answer “how much better?” FDA is requiring Moderna to run that head-to-head trial, but results won’t be in for a year or two. In the meantime, they authorized its use for people ages 65 and older through an accelerated approval.

2. Will people be able to get it this fall? Yes, maybe, I think?

For those aged 50-64, it’s unclear whether this will be widely available. Traditionally, ACIP has to recommend a new vaccine for insurance to cover it and for physicians to order it. But ACIP isn’t functioning because of a legal dispute between AAP and RFK Jr. It’s unclear what happens in fall.

For those 65 and older, there is a loophole: flu vaccine coverage under Medicare Part B is written directly into the law. It doesn’t depend on ACIP. That means people 65+ on Medicare should be able to get it this fall at no cost.

3. Will people actually get vaccinated?

This is the elephant in the room: flu vaccination rates are decreasing across the country at staggering rates. Shiny new biotechnology is cool, but not if people don’t use it.

Poll

Bottom line

Covid-19 is resurging, rare mosquito-borne diseases are gaining ground, and illnesses from the 19th century are making an unwelcome return. The tools to stop them exist (and new ones are coming), but the question is whether we’ll use them.

Love, YLE

Your Local Epidemiologist (YLE) comprises a team of experts, ranging from physicians to immunologists to epidemiologists to nutritionists, working together with one goal: to “translate” ever-evolving public health science so that people are well-equipped to make evidence-based decisions. The YLE suite of newsletters reaches over 475,000 people across more than 132 countries. This newsletter is free to everyone, thanks to the generous support of fellow YLE community members. To support the effort, subscribe or upgrade below: