The U.S. measles vaccine program has reduced cases from more than 700,000 a year in the 1950s to a low of 37 in 2004. This week, U.S. measles cases have climbed to their highest level in 25 years.

The California Department of Public Health issued a health advisory on April 25 urging Californians traveling internationally to be fully vaccinated against measles. In 2019, there have been 38 cases of measles in California. This is an increase of 15 cases from last week, and compares with 11 cases at this time in 2018. Of the 2019 cases, 14 cases were in international travelers, 22 cases were due to spread from travelers to persons in California, and 2 cases are of unknown source.

Do you need another measles vaccine? Consult with your doctor. There is a chance that some people vaccinated with the first vaccine in 1963 could need another shot with the later-developed live vaccine in use from 1968 to today, according to the Centers for Disease Control and Prevention.

The CDC issued the following caution: If you received a measles vaccine in the 1960s, you may not need to be revaccinated. People who have documentation of receiving LIVE measles vaccine in the 1960s do not need to be revaccinated. People who were vaccinated prior to 1968 with either an inactivated (killed) measles vaccine or a measles vaccine of unknown type should be revaccinated with at least one dose of live attenuated measles vaccine. This recommendation is intended to protect those who may have received killed measles vaccine, which was available in 1963-1967 and was not effective.

Children are very vulnerable and need 2 doses of vaccine.

The CDC recommends that children get one dose at each of the following ages:

12 through 15 months

4 through 6 years

You don’t need the new vaccine if: You’ve had measles, you were born before 1957 or you’ve had a lab test that shows you’re immune to measles. If you don’t know your status, ask your doctor about the shot anyway unless you are pregnant or have a weakened immune system.

The CDC has a full measles, mumps, and rubella vaccination breakdown.

On April 24, 2019, Health and Human Services Secretary Alex Azar said, “Measles is not a harmless childhood illness, but a highly contagious, potentially life-threatening disease. We have the ability to safely protect our children and our communities. Vaccines are a safe, highly effective public health solution that can prevent this disease. The measles vaccines are among the most extensively studied medical products we have, and their safety has been firmly established over many years in some of the largest vaccine studies ever undertaken.”

Traces of measles can be found in the air or on surfaces as long as two hours after an infected person has coughed.

How contagious?

In epidemiology, the basic reproduction number, R0 (pronounced “R naught,”) is a mathematical term that indicates how contagious an infectious disease is. Here’s how measles compares in maximum R0 values to other infectious diseases.

According to the World Health Organization, reported cases of measles increased by more than 30% from 2016 to 2017. The reported worldwide total in 2017 was 173,330.

Top 5 countries in 2018:

India 38,505

Ukraine 23,070

Philippines 7,894

Nigeria 5,451

Serbia 4,954

Sources: Centers for Disease Control and Prevention, The Washington Post, NPR, The Washington Post, Health and Human Services

Additional reporting by Charles Apple