After a few weeks of nosediving, things are, unfortunately, stabilizing. Does it feel like this respiratory season is never-ending? That’s because this is the longest respiratory season since the beginning of the pandemic.

Here is your state of affairs.

Influenza-like illnesses: High and plateauing

The climate of respiratory health in the United States (coined “influenza-like illnesses” by CDC) remains above the epidemic threshold and has plateaued due to children returning to school after the holidays.

We are going into our 13th week of being above “epidemic” levels. Last year, our entire season was 11 weeks. (The year before was 7 weeks). It’s looking more and more like “pre-pandemic” times, where we had ~15-18 weeks of illness during the winter.

Outpatient Respiratory Illness Visits (Source: CDC; Annotated by YLE)

Covid-19 still takes the cake for respiratory deaths. By how much? We don’t know yet. The data below are from death certificates, which are pretty accurate for Covid and RSV but not for flu. CDC annually adjusts flu deaths post-hoc to account for underreporting. We must wait to see how those calculations play out.

Trends in Viral Respiratory Deaths in the United States (Source: CDC; Annotated by YLE)

Covid-19: High and… stabilizing? 

Nationally, Covid-19 in wastewater is still “high.” Unfortunately, levels have stabilized in all regions except the South, where exponential growth started again. This could be a “noise” signal due to unstable reporting or a “real” signal due to, perhaps, it getting colder later in the South.

Wastewater SARS-CoV-2 viral activity level on a national level (Source: CDC; Annotations by YLE)

Covid-19 hospitalizations are slowing down, too, after a few weeks of nosediving. Are Covid-19 hospitalizations higher than flu? Well… it depends on which CDC graph you look at, which is confusing. The top graph below shows Covid-19 hospitalizations winning while the bottom shows flu winning.

(Top) Covid-19 and Influenza Hospitalization Rates (Source: CDC) (Bottom) Weekly Rates of Respiratory Virus-Associated Hospitalizations by Season (Source: CDC); Annotated by YLE

Why the different data stories? The sources are different. The top graph is from all hospitals mandated to report due to the pandemic, and the bottom is a few hospitals representing only 10% of the population from mostly urban areas. This is probably causing two things to happen:

1. Vaccine effect. Urban places have more Covid-19 vaccinated than rural; thus Covid-19 hospitalizations are lower on the bottom graph than the top.
2. Case definition differences may be happening. The data in the top graph is reported by hospitals, which may differ from the bottom graph, reported by a review of lab records.

I trust the top graph more. Unfortunately, this data story will stop in April because the reporting mandate is ending. Hospitals hate reporting this metric, but if you ask me, I don’t care. We need this data.

Flu: High and stabilizing

Influenza is still surging. Emergency department visits for flu increased due to one particular group: 5-17 year olds.

Percent of Emergency Department Visits for Flu, by age. (Source CDC; Annotated by YLE)

RSV: Moderate but nosediving

RSV continues to go down and down. Good riddance.

(Source: CDC)

Other things I’m paying attention to:

• New CDC data show that the 2023 fall Covid-19 vaccines provide 54% increased protection against infection. In other words, fall Covid vaccines were a good call. A few more thoughts of mine are here.
• Norovirus (think throwing up and diarrhea) has been a rollercoaster, but is now increasing quickly. Historically, this is about the time that norovirus takes off. Wash those hands.

(Source: CDC)

Bottom line

We are still very much in the middle of the “feeling crappy” season. And, unfortunately, it’s already longer than last year’s. Hopefully we get a reprieve in the next month or two.

Love, YLE

“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, M.P.H. Ph.D.—an epidemiologist, wife. During the day, she is a senior scientific consultant to several organizations, including CDC. At night, she writes this newsletter. Her main goal is to “translate” the ever-evolving public health world so that people will be well-equipped to make evidence-based decisions. This newsletter is free, thanks to the generous support of fellow YLE community members. To support this effort, subscribe below:

Measles continues to pepper the news:

• A new outbreak in Georgia
• Report last week of a 45-fold rise in measles in Europe
• CDC released a national alert for physicians to keep an eye out for cases

I am getting a lot of questions! Here’s what you need to know if you’re fully vaccinated.

Can I get measles if I’m fully vaccinated?

The MMR vaccine works incredibly well—you’re 35 times less likely to get measles than someone with no immunity.

But nothing is perfect. A breakthrough case is rare but possible (3 out of 100 fully vaccinated people will get infected). The disease does tend to be milder.

We don’t know why there are breakthrough cases, but there are two possibilities:

1. Waning immunity (see more below); or
2. Vaccine didn’t work in the first place for whatever reason. 5% of people do not get protection after the first dose, but 95% of those will be fully protected after a second dose.

If I am exposed, can I transmit measles?

Transmission after vaccination, especially if you’re asymptomatic, is rare:

• We see this in the lab data. A small study found no viral shedding among asymptomatic or mildly ill patients. But this is a very old study, and we need to replicate findings with more sensitive lab equipment.
• We see this in the epidemiological data. While there are several studies showing spread among vaccinated people, especially after intense or prolonged exposure, the epidemiological implications don’t seem to be dramatic. In other words, cases don’t transmit enough to sustain outbreaks.

In 2011, there was a well-documented outbreak in New York. This was the first documented measles outbreak where the index case had two doses of MMR. Out of 88 close contacts, 4 got infected and had symptoms. Those who got infected had more than 200 contacts, and none got measles. (Note: We would expect ~90% to get infected if this population didn’t have immunity.)

Figure by YLE

Why does the measles vaccine work better than the Covid-19 vaccine? 

These are very different viruses:

1. Mutates differently. Measles is much more restricted in how it mutates compared to Covid-19. For example, new versions of measles don’t come out every few months to escape our immunity. The 1960 measles virus is largely the same today. (See this previous YLE post for more).
2. Infects differently. Measles is a lot slower at infection. It requires going deep into the body to start replicating. Because of this, the measles vaccine is much better at stopping transmission, as our body has much more time to control measles infection. This is different from Covid-19, which replicates on the surface of the nasal cavity very quickly. It’s hard for our cells to reach it in time to prevent replication.

If we are protected from measles for life, why are there booster rumors?

I think this happening for a few reasons:

1. MMR combines protection for three diseases into one shot: Measles, mumps, and rubella. Each of these wanes at different rates, which is confusing:
   1. Measles. Measles antibodies are incredibly durable (the most durable of the three) but wane over time. This isn’t too concerning because we have T cell protection, too. Studies that followed people for 17 years showed the vast majority (~91%) remained above the threshold needed for protection. What happens if they continue to wane? We are at the mercy of time, but currently, outbreaks continue to occur among unvaccinated people.
   2. Mumps antibodies are also durable but wane faster than measles. Approximately 25% lose protection within 8 years and 50% within 19 years of vaccination. This is why some consider a third dose of MMR before kids go to college.
   3. Rubella wanes, too, but you’re generally considered fully protected for life. Recent studies showed that the younger a person is, the quicker it wanes. This raises the question of whether women, especially those who get pregnant at an older age, need another booster.

2. Other countries are discussing the possibility of a measles booster, for example for health care workers in Korea. Studies show a booster provides benefits, but they are short-lived.
3. The guidance says if you were born before 1957, it is assumed you had measles and you’re fully protected. This group can probably skip getting MMR for measles protection unless other factors are at play (e.g., chemotherapy).

As vaccines have started eliminating diseases, people’s exposure to those diseases in the community has declined. This is good news, but it also means our immune systems have had less opportunity for boosting by asymptomatic infections (i.e., hybrid immunity). We don’t know the implications of this, but we are keeping a close eye on the data.

I hear measles infection-induced immunity is more durable than vaccine-induced immunity?  

This is true. Infection-induced antibodies wane less quickly among adults and fetuses compared to vaccine-induced immunity.

The problem is that an infection comes with many more risks than a vaccine. If I were to bet on it, I would rather have the odds on the right than left.

Are babies protected if their mom was fully vaccinated? 

Anyone trying to conceive should have MMR titers checked, and if levels are low, MMR should be administered 28 or more days before conception.

The vast majority of moms transfer antibodies of all three—measles, mumps, and rubella—to fetuses. Once born, antibodies wane really quickly and are almost all gone at 6-12 months of age.

So why do we wait until 12 months to get children vaccinated? 

We try to get to the sweet spot by balancing a few factors: maternal antibodies waning, maturity of the immune system, and the most common age of infection. For example, maternal antibodies can greatly reduce the infants response to the MMR vaccine. So we want to be sure these wane before getting a child vaccinated.

That said, if there is a measles outbreak, protection is needed ASAP for young children. Early vaccination is one provisional measure we can take.

Bottom line

If you’re fully vaccinated, you can be confident in your protection. We continue to follow the data, but failure to vaccinate still plays the biggest role in measles in the United States compared to vaccine failures.

Love, YLE