Measles Outbreaks Could Occur in These States

In recent years, a growing vaccine hesitancy movement has contributed to decreasing measles vaccination rates in Europe and the USA. 

Even if a US state has an average vaccination rate approaching herd-immunity, about 95 percent, measles outbreaks can still occur if there exist localized communities with a high proportion of unvaccinated individuals, and, if the community is highly connected by travel to international regions experiencing large outbreaks, reported a study published in The Lancet on July 30, 2020.

In response to these persistent risk factors, these researchers expanded upon previous work to identify the set of US counties at the highest risk of measles outbreaks.

Multiple regions in California, Florida, New York, Washington, and Texas are identified as being of the highest risk of measles outbreaks, which is concordant with the 2019 outbreaks.

The risk to each county was computed with a multiplicative function of four factors: incidence rate of measles at travel origin, international air travel volume from each such origin to a US destination county, measles, mumps, and rubella (MMR) vaccination rates in the county, and county population.

Results from the model are illustrated in the figure in Appendix 1, which shows the percentage of the population unvaccinated for measles in each US county, the location and relative size of the reported measles outbreaks in 2019, the location of the 20 most visited airports in the USA, and the 30 counties at highest risk of measles outbreaks.

Of the 20 highest ranked counties, together they reported over 700 of the 1,276 confirmed cases in the USA. The model indicates the cities of Los Angeles (CA), Seattle (WA), Honolulu (HI), Miami (FL), and Santa Ana (CA) to be the 5 counties at highest risk.

As an example, the Los Angeles County Department of Public Health confirmed a measles outbreak among 5 persons on February 5, 2020. This measles outbreak began when a measles infectious international visitor was visiting the greater Los Angeles area.

Furthermore, the Philippines, Samoa, Ukraine, New Zealand, and Israel are the countries of highest risk for measles importation to the USA. 

The 4 air travel routes posing the highest risk of measles importation ended in Los Angeles and originated in the Philippines, Samoa, New Zealand, and Ukraine. 

The top 100 US counties and travel routes are listed in Appendix 2.

Measles is considered among the most contagious viruses in the world. About 90 percent of people who have never been immunized against measles become ill 7-21 days after exposure. 

Infected people can infect those around them before they have symptoms and know they are infected, says the U.S. CDC.

The CDC stresses MMR vaccinations prior to international travel.

Unfortunately, a Massachusetts General Hospital study published on December 9, 2019, found a large number of children traveling abroad are not protected from the measles virus. This study was published in JAMA Pediatrics and reported about 44 percent of MMR vaccination–eligible infants were not protected.

Besides the measles vaccines, the CDC encourages travelers to speak with a healthcare provider regarding other travel vaccines options.

Vax-Before-Travel publishes research-based international travel vaccination news.