Tag: measles seasons

When is Measles Season?

For a while, especially once we eliminated the endemic spread of measles, we weren’t thinking about measles seasons anymore.

In addition to the recent rise in measles cases, this slide shows the patterns of measles seasons in different parts of the world.
In addition to the recent rise in measles cases, this slide shows the patterns of measles seasons in different parts of the world.

Unfortunately, with ongoing outbreaks and rising cases, many people are asking again – just when is measles season?

When is Measles Season?

Traditionally, the time when measles case counts are the highest occurs:

  • during the late winter and early spring (temperate climates, like the United States)
  • after the rainy season (tropical climates)
  • when kids are in school

So just like flu season, it’s always measles season somewhere…

And in areas of the world where measles is still highly endemic, you can expect cycles of larger measles epidemics every 1 to 4 years.

Can you guess why?

“As higher uniform population immunity is achieved the scale of epidemics, both their duration and absolute number of cases, progressively decreases. Epidemic frequency simultaneously decreases with increasing time intervals between epidemics. Another uniform feature as elimination is approached is the loss of epidemic seasonality.”

Durrheim et al on Measles – The epidemiology of elimination

I’ll give you a hint – there is nothing different about the measles virus during those years.

Eventually though, as the number of people susceptible to measles builds up, there is the opportunity for bigger outbreaks. Of course, that doesn’t happen if most people are vaccinated and protected.

When is Measles Season in the United States?

What about in the United States in the post-vaccine era?

Visiting a place with a lot of measles, especially if you aren't vaccinated and protected, increases the risk that you will bring measles home with you and start an outbreak.
Visiting a place with a lot of measles, especially if you aren’t vaccinated and protected, increases the risk that you will bring measles home with you and start an outbreak.

We don’t really have a measles season, as all of our cases are now imported from other parts of the world.

  1. Where and when are folks traveling?
  2. Where is measles on the rise?

That’s when we will see more measles cases here.

“Source countries included Philippines (14 cases), Ukraine (8), Israel (5), Thailand (3), Vietnam (2), Germany (2), and one importation each from Algeria, France, India, Lithuania, Russia, and the United Kingdom.”

Increase in Measles Cases — United States, January 1–April 26, 2019

In the early part of 2019, we saw a lot of cases because unvaccinated travelers were returning from Philippines, Ukraine, and Israel, countries in peak measles season.

Are Europe's measles outbreaks slowing down yet?
Are Europe’s measles outbreaks slowing down yet?

As cases in those countries hopefully slow down over the summer, unfortunately, we might see a rise in other parts of the world.

Of course, there is an easy way to end our measles seasons once and for all.

Two doses of MMR is your best protection against measles.

Get vaccinated and protected, especially before traveling out of the country.

More on Measles Season?

Is January Usually a Big Measles Month?

This year is just getting started, but we already have reports of 86 92 94 measles cases in 7 states, and we haven’t even reached the end of January.

Is that a lot?

Well, let’s compare to previous years…

Is January Usually a Big Measles Month?

Classically, in the pre-vaccine era and in parts of the world that still have endemic measles, rates of this vaccine-preventable disease are highest:

  • during the late winter and early spring (temperate climates, like the United States)
  • after the rainy season (tropical climates)

In the post-vaccine era, measles season seemed to shift a little later, to the spring and early summer. In 1994, for example, when we had 963 cases of measles in the United States, 79% of those cases occurred between April and July.

January is not typically a big month for measles.
January is not typically a big month for measles.

Similarly, in 2011, we had only seen 15% of the year’s total measles cases by April 1. By August 1, that was up to about 70%.

We do see measles cases year round though, we just seem to see more of them in the spring and early summer months. Since most measles outbreaks in the United States are imported from other parts of the world, you might expect that we would see more cases when folks are traveling more and when there are big outbreaks in other parts of the world.

Unfortunately, measles is on the rise in many parts of the world right now.

And that is likely why we have already seen more cases this month than in the entire year of 2000 (86 cases), 2002 (44 cases), 2003 (55 cases), 2004 (37 cases), 2005 (66 cases), 2006 (66 cases), 2007 (55 cases), 2009 (71 cases), 2010 (61 cases), and 2016 (86 cases).

YearJanuary Measles CasesTotal Cases
19915969,643
1992492,200
199317312
19946963
199522309
19962508
20081140
20118220
20137187
201415667
2015108188
20188355
201994?

As you can see from the above table, January is not typically a big month for measles.

But what happened in 2015? There were a lot of measles cases in January, but we ended the year with only a moderate amount of cases.

That January spike was the California outbreak that had begun in December 2014. By February 2015, there were at least 125 cases, but fortunately no other large outbreaks the rest of the year.

Could that happen this year?

Could the ongoing outbreaks in New York and the Pacific Northwest stop and we then end up with only a moderate amount of cases?

Let’s hope so.

Let’s hope that having the second highest number of measles cases in January since 1991 ends up being the only record we set this year.

More on Measles Season