As we sweat through the last days of winter, it’s a chance to consider how warming trends impact our health in California. The whiplash of federal vaccine policy swings continues—thanks to state foresight, we’re fortunate to see this from a safer, science-based distance. RSV is an outlier in lingering late this season. And I share another adventure in preventive care. Let’s jump in.
Under the weather after the shingles vaccine, and fine with it
Yesterday I got my shingles vaccine. I’m clearly catching up on some deferred maintenance after my colonoscopy two weeks ago. I hope my examples can encourage you to tend to any preventive care you’ve put off.
The vaccine has left me feeling achy, tired, and a little feverish. That’s normal— it’s a sign my body is mounting a healthy immune response. I’ll be better tomorrow. Here’s why it’s worth it.
What is shingles? Shingles is caused by varicella-zoster virus—the same virus that gave a lot of us chickenpox as kids. After that childhood infection, the virus retreats into nerve tissue and waits, sometimes for decades. In about one in three adults, it revives again, causing a painful, blistering rash later in life called shingles. In some cases nerve pain can persist for months after the rash goes away. All highly worth avoiding.
The vaccine works. In adults aged 50–69, the shingles vaccine is about 97% effective at preventing shingles. It’s 91% effective in adults 70 and older. And protection lasts—newer research shows about 80% efficacy up to 11 years after vaccination.
The benefits may extend to brain health. A 2024 study of more than 200,000 older Americans found that people who received the current shingles vaccine had 17% more “dementia-free days” compared to those who hadn’t. It’s not clear why—it’s possible the virus triggers neuroinflammation, accelerating dementia. Vaccination could reduce that insult to the brain.
Who should get the vaccine? The recommendations are simple and clear: two doses of shingles vaccine (Shingrix) for all adults 50 and older, two to six months apart. This vaccine is well studied and recommended without much controversy (even in these turbulent times) by every major medical organization. If you’re 50 or older and haven’t gotten it, this is your nudge. You can find vaccines in California at MyTurn.ca.gov.
Winter heat wave
It’s still winter, but most of us are getting a preview of summer. We’re sweating through one of the most intense early-season heat waves ever, with San Francisco, Los Angeles, and Sacramento breaking March temperature records. Friday, March 20 is forecast to be the hottest day during this event in many areas.
A “heat dome”—a pocket of high pressure parked over most of California—is trapping hot air near the surface, where we live and breathe.
Off-season heat waves can be more risky because we’re not acclimated yet, and people may not take the precautions that come more naturally in summer. Here’s a reminder of the measures to take.
What you can do now:
Stay hydrated and drink water regularly, even if you’re not thirsty.
Limit outdoor activity during the hottest afternoon hours.
Seek air-conditioned spaces if your home becomes too warm.
Never leave children or pets in cars.
A hat can provide simple but effective shade.
Check on older neighbors or relatives, especially those without air conditioning.
I want to highlight this last one. Studies show that social isolation is a key risk factor for bad outcomes in heat waves. Many of the over 700 people who died in the 1995 Chicago heat wave were older adults living alone, without someone to recognize the danger or check in. A simple check-in from a neighbor or loved one can make the difference.
The bigger picture. It’s hard to say any one heat event is due to climate change—but it’s a mistake to ignore the trends. It’s plain hotter now than it was a few decades ago. In fact, if you were born in the 1980s, it’s roughly 2°F warmer on average than when you were a kid. This chart shows the patterns over the past 150 years, with the sharpest annual rise in the past 40 years.
Global average annual temperature, relative to early 1900s
Heat waves happen with more frequency and intensity as average temperatures rise, but there are other health risks related to warming trends in California. Each of these deserves its own spotlight—I’ll cover them in deeper dives in the months ahead.
Wildfires and wildfire smoke: Hot, dry conditions—and a poor Sierra snowpack this year—leave forests more fire-prone. Smoke worsens asthma and heart disease and drives emergency visits.
Water quality: Warmer temperatures promote harmful algal blooms and strain drinking-water systems during drought.
Mosquito-borne disease: Heat expands the range and season of mosquitoes carrying viruses like dengue and West Nile.
Air quality: Smog forms more quickly in hot weather, irritating lungs and worsening respiratory disease.
Longer allergy seasons: Warmer temperatures are linked to longer, more intense pollen seasons.
Looking ahead. It’s easy to feel helpless in the face of warming trends. I find it helpful to think along short and long term paths: 1) focus on measures to stay safe during todays’s climate-related events, like this heat wave, and 2) work to reduce the greenhouse gas emissions that are driving these changes long term. There’s a lot we can do on both fronts.
Most medical and public health organizations see climate change as a core health issue, supporting policies that reduce emissions while improving health. For anyone interested in learning more or joining this effort, the Medical Society Consortium on Climate and Health and University of California San Francisco Center for Climate, Health and Equity are good options.
There’s also an increase in refreshingly bipartisan efforts to tackle climate change. I like RepublicEn, which is led by Bob Inglis, a former Republican congressman from South Carolina.
A note on climate coverage: In our recent survey we learned many of you would like more coverage of environmental health issues, including climate threats. It’s been an area of focus over my public health career, and I hear you loud and clear.
Climate change is too big to tackle in one piece. So I won’t. Instead, I’ll keep connecting the dots between the health issues we’re facing in California, as they arise, and the climate trends driving them. We’ll take each heat wave, each fire, each shift in disease patterns as both a signal and a chance to take action.
California’s early move on vaccines is paying off
This week a federal judge put a freeze on the changes RFK Jr. has made to federal vaccine recommendations, stating that advisory committee (ACIP) team members weren’t appointed legally, and that they failed to follow scientific standards in decision-making.
The ruling is good news for the nation, and a win for science—but doesn’t change a lot for us in practical terms in California.
When California saw the direction federal vaccine policy was heading last year, our leaders created a new law, Assembly Bill 144, which de-coupled state vaccine recommendations and access from CDC guidance. The goal was to protect science- based policies, and shield us from federal faltering. That move showed a lot of foresight.
And California isn’t alone. Now, 30 states—across both Democratic and Republican leadership—are declining to follow at least some elements of recent ACIP guidance, in favor of evidence-based practice.
What this means for us (not much):
Vaccine recommendations in California have not changed (aside from the extension though April for infant RSV mentioned below.)
School immunization requirements are the same.
Insurance coverage for vaccines remains protected.
Clinicians are still following evidence-based schedules.
The bigger picture. We’re entering an era where vaccine standards are increasingly state-driven, rather than a single national approach. We’re fortunate to be protected in California. Still, the back-and-forth changes to federal guidance can be confusing for families, clinicians, and schools, even when access is protected. For a deeper dive into the ruling and what it means nationally, read Katelyn’s YLE National piece from Tuesday.
Seasonal virus “weather report”
Flu activity continues to decrease across California. Flu A is dropping rapidly, while Flu B levels remain at a plateau.
Covid-19 levels remain low.
After a late start to the season, RSV levels are still elevated. As a result, the recommended window to immunize babies has been extended through April in California.
Bottom line
That’s it for this week. Stay cool out there, and check in on anyone who might need it. As always, we love your feedback about what you’d like to hear more about.
Love,
Matt
Dr. Matt Willis is the author of Your Local Epidemiologist in California. A California native, he’s served as a primary care physician, CDC epidemiologist, and public health officer for Marin County, where he guided the pandemic response. He lives in Marin with his family and their dogs Teddy and Ramona.
I hope your vaccine side effects are brief, as they usually are. I read every YLE post; in one, Katelyn suggested avoiding science or data in debate. I understand using a concern-based approach for vaccines, but I’m at a loss when it comes to climate change. Most of my family are deniers, yet they frequently talk about extreme weather—it amazes me that some can deny the very issue they discuss.
Thanks Matt. I hope everyone 50+ gets the shingles vax. I got the single shot vax and then a couple of years later did get shingles but had only four spots. It was a miserable experience for a month. I kept thinking about how the vaccine probably kept the rash away. When the two-shot version came out, I got that. Months later I had a second case of shingles but with just two spots and not much misery. Both times I did not realize it was shingles due to lack of a big rash but my doc knew. I think my experiences illustrate how vaccines may not totally prevent a virus from affecting us but they do reduce severity a lot. So glad I chose to spend my fairly limited retirement funds on those shots.