Is measles making a comeback?

Infectious Diseases

Measles outbreaks happen every year but are becoming more common as vaccination rates decline.

There have been several US measles outbreaks so far this year, including multiple in Florida, California and Washington state. Many began with an international traveler returning home, which is typical for measles outbreaks.

Because measles is so contagious, vaccination rates need to be very high (~95%) to maintain herd immunity. When local communities dip below this threshold, they are vulnerable to outbreaks.

As an example, Washington state was hit hard during a 2019 multi-state measles outbreak, the largest nationally in the last 20 years. At the time, statewide vaccination coverage with at least one 1 MMR (measles, mumps, and rubella) dose by preschool was only 75%, meaning measles could spread very easily. Since that time, some counties have improved coverage to 85%, but many others hover around 50%, sometimes lower. Washington is just one of 35 states with vaccination rates for 2 MMRs by kindergarten less than 95%, which leaves an environment ripe for outbreaks to occur.

Measles is a respiratory virus that spreads through droplets or the air when someone who has measles coughs, sneezes, or talks. Measles is *very* contagious-about 90% of unvaccinated people who have close contact with an infected person will get measles. The measles virus can stay in the air for up to 2 hours after an infected person has left the room.

Measles can be very serious. About 20% of unvaccinated people who contract measles will end up in the hospital, and many will get sick or die from secondary infections. In unvaccinated people the disease depletes B and T cells, essentially removing the parts of the immune system that “remember” how to fight off a prior disease. For this reason, unvaccinated people recovering from measles are more likely to get pneumonia, brain infections, and even common colds and viruses, an effect that can last 2-3 years.

Although it is possible for a vaccinated person to get measles, it is very rare. If a vaccinated person does get sick, the disease tends to be more mild.

We might be seeing more measles outbreaks because overall vaccination rates decreased during the COVID-19 pandemic. Small decreases in vaccination coverage mean big increases in measles cases, where one sick person can infect ~18 other people. (In contrast, one person with COVID-19 is thought to infect about 1 to 3 people).

All states but one require 2 doses of MMR by kindergarten, but 17 states allow philosophical exemptions, meaning parents can decline without medical documentation or strongly held religious beliefs (Washington state dropped its philosophical exemption for MMR after the 2019 outbreak). Even if your state requires this vaccine, childcare and school-level exemptions may drop vaccination coverage for measles far below 95%.

How can I protect myself and my family with the recent outbreaks?

➡️  Vaccinate your child with MMR at age 1 and 4. MMR provides 93% protection from measles with one dose and 97% protection with two doses. Higher levels of community vaccination protect those who cannot receive MMR, like babies less than 6 months of age.

➡️ A high-quality respirator (e.g. KF94 mask) might be helpful during an outbreak or as an added precaution during travel. This is especially important for pregnant and immunocompromised people, since they are ineligible for the MMR vaccine.

➡️ If you are traveling anywhere outside of the U.S. (even Canada!) with an infant 6-11 months of age, check with your pediatrician about getting an extra MMR before travel. These infants will still need their scheduled dose at 12 months.

Measles has never completely gone away. Although it does not typically circulate continuously in the US, a 30-fold increase of cases in Europe makes it even more likely that there will be more outbreaks stateside. If vaccination rates continue to drop, measles could return as a part of daily life, which is NOT GOOD! If you’ve got friends or family with young kids, talk to them about the importance and safety of the MMR vaccine.

Stay safe. Stay well.

Those Nerdy Girls

Further reading

Measles and Immune Amnesia

Measles FAQ from the CDC

Link to Original Substack Post