In light of the current measles outbreak in the United States, we asked Dr. Christopher Sanford, author of Staying Healthy Abroad, to break down the statistics on measles nationally and globally for travelers across the country. He also answers some commonly asked questions about immunity and vaccinations.
The purpose of this article is educational. For medical advice for any health condition, please consult your physician.
Over 700 people in 22 US states have been infected with measles this year—the biggest measles outbreak in the US since 1994. Sixty-six of these people have required hospitalization. Most of those with measles had not been vaccinated for measles.
Per the WHO (World Health Organization), global measles deaths have decreased significantly in recent years, from 550,000 deaths in 2000 to 90,000 deaths in 2016 (an 84% reduction), but measles remains common in many low-income nations, particularly in Africa and Asia. An estimated 7 million people were infected with measles in 2016.
People immunized before 1989 may have only received one dose of measles vaccine. This provides partial protection, but better protection is provided by receiving a booster dose, that is, two doses of MMR (measles-mumps-rubella) total.
International travelers should receive a total of two doses of MMR vaccine. If travelers are uncertain as to their vaccine status, they may request serology (a blood test) from their medical provider to look for immunity. Those born before 1957 in the US are assumed to be immune to measles, mumps, and rubella from prior natural infection; vaccination with MMR is not advised.
Almost all US and Canadian universities and colleges began to require evidence of two prior doses of MMR vaccine (or proof of immunity) in about 1994.
Measles is a serious viral infection that is transmitted by coughing and sneezing. The virus can live for up to two hours in an airspace or on a surface. Usual symptoms are fever, cough, rash, runny nose, and conjunctivitis (pinkeye). Although most people fully recover, complications include encephalitis—swelling of the brain which can result in permanent brain damage or death—and pneumonia.
The usual case-fatality rate in measles is 1-2/1,000 (0.1-0.2%). However, in malnourished populations, the case-fatality rate can approach one in ten.
In order to prevent sustained transmission of measles, 95% of the population needs to be immune, either from vaccination or natural infection (“herd immunity”).
In the US, in the decade 1912-1922, measles caused an average of 6,000 deaths per year. Prior to 1963, when measles vaccination became available, measles caused 4,800 hospitalizations, 1,000 cases of encephalitis, and 400-500 deaths each year in the US.
In the current measles outbreak in Washington State, there have been 71 cases in Clark County (in southwest Washington, adjacent to Portland, OR) and one case in King County. The majority of these cases were in unimmunized people.
There are currently measles outbreaks in 22 US states.
There were 372 cases of measles in the US in 2018. Between January 1 and April 26 of this year, 704 cases have occurred.
Most US cases are in children. Per a April 9 article in the Wall Street Journal:
New York City officials declared a public-health emergency as authorities elsewhere in the state announced new measures to halt the spread of measles, stepping up their responses after a recent surge in cases. The city on Tuesday ordered mandatory measles-mumps-rubella vaccination and fines for noncompliance in certain ZIP Codes in Brooklyn.
The current US vaccine schedule for measles: two doses; first at 12-15 months, second at 4-6 years. Boosters after initial series of two are not advised.
The dramatic decline in global measles is primarily due to increased vaccine coverage in low-income nations. However, should vaccine efforts wane, measles cases and deaths would inevitably markedly increase.
Many countries in Europe have seen a large uptick in measles cases in recent years. There are currently outbreaks in Germany, Ireland, Italy, France, and other European countries. Countries outside of Europe with current outbreaks include Israel, Ukraine, and Australia.
What’s the difference between elimination and eradication?
Eradication is the complete and permanent worldwide reduction to zero new cases of a disease through deliberate efforts. Smallpox has been eradicated from the planet. Elimination is the reduction to zero, or a very low defined target rate, new cases of a disease in a specified geographical areas. Measles was declared to be eliminated from the US in 2000.
How effective is measles vaccine?
Very. The two-dose series provides 97% protection.
What is herd immunity?
If a certain threshold level of a community is immune to a disease, either through infection or immunization, that infection cannot be propagated within that community. The threshold for different infections varies. For example, the level of resistance for polio in a community necessary to prevent an epidemic is 80%. Measles is more infectious; about 95% of a community needs to be resistant to measles to prevent epidemics.
What is the current measles vaccine rate in the US?
Fairly high. Currently, per the CDC, 94.3% of kindergartners were current for measles vaccine in the 2017-18 school year. However, this rate is markedly lower in some communities, e.g., the Orthodox Jewish community in Brooklyn, NY, and Clark County, WA, in which measles epidemics are currently occurring.
How can I tell if I’m immune to measles?
If you’ve received the two-dose series of MMR (measles, mumps, rubella) vaccine, it is reasonable to assume that you’re immune. If your vaccine history is uncertain, options include a blood test to check immunity, or receiving the two-dose series.
Christopher Sanford, MD, MPH is associate professor in the Departments of Family Medicine and Global Health at the University of Washington, and a family medicine physician who specializes in tropical medicine and travelers’ health. His research interests include medical education in low-resource settings and health risks of urban centers in low-income nations.