Preventing Measles: Effectiveness of Immunization at 9 Months of Age

Measles, a highly contagious and potentially deadly disease, is preventable through vaccination. The MMR (Measles, Mumps, and Rubella) vaccine is a crucial tool in the fight against measles, with immunization at 9 months of age a key milestone in a child's vaccination schedule. While the two-shot series offers an impressive 97% effectiveness rate, concerns arise regarding the prevention of measles in an unvaccinated population. This article will delve into the effectiveness of the MMR vaccine, the success of measles elimination in the U.S., and the importance of vaccination in preventing the spread of the disease.

Effectiveness of the MMR Vaccine

The MMR vaccination is typically administered in two doses: the first at 12 months of age and the second at 4 years of age. The initial dose is 93% effective against measles, but the second dose significantly increases the efficacy to 97%. These statistics highlight the critical role of the two-dose series in providing robust protection against this highly infectious disease.

Understanding Prevention Percentages

The effectiveness rate of 97% refers to the percentage of measles cases that are prevented through vaccination. It is important to note that this does not translate directly to the number of deaths or cases of measles. For instance, while the vaccine can effectively prevent the vast majority of cases, it does not guarantee the complete eradication of the disease. In some cases, despite vaccination, an individual may still be infected. Hence, the prevention percentage is based on the protection offered rather than an absolute guarantee of non-infection.

The Role of Unvaccinated Populations

In an unvaccinated population, the scenario is markedly different. Measles will spread rapidly, much like a wildfire. This scenario is based on historical data and theoretical models, as intentionally foregoing vaccination for research purposes is unethical and illegal. As such, discussions around the prevention rate often come with caveats.

Measles Elimination in the U.S.

The United States has made significant strides in the fight against measles. For many years, there were virtually no cases of the disease, thanks to widespread vaccination. However, the resurgence of anti-vaxxer propaganda has led to a rise in cases. Despite continued importations of the virus, the number of measles cases in the U.S. has significantly dropped. For instance, during the period of 2001 to 2008, there was a median of 56 cases reported annually. In 2011, the first 19 weeks saw a spike of 118 cases, the highest in nearly two decades. Prominent among these cases were 105 individuals who were unvaccinated, highlighting the critical role of vaccination in preventing disease spread.

Imported Cases and Delayed Vaccination

The majority of the 2011 cases were associated with importations. Of the 118 cases, 46 were importations from other countries, including 34 U.S. residents who had traveled abroad and 12 foreign visitors. Among these importations, 40 were from the World Health Organization's (WHO) European and South-East Asia regions. In that same period, 47 patients required hospitalization, and nine had pneumonia, underscoring the severe health implications of measles.

The Importance of Vaccination

One of the most striking findings is that babies are less likely to get measles if the people around them are vaccinated. Herd immunity plays a crucial role in preventing the spread of the disease. Even a small number of unvaccinated individuals can act as a breeding ground for the virus, leading to outbreaks. Vaccination is not only about protecting the individual but also about protecting communities, especially those who cannot be vaccinated due to age or health conditions.

Conclusion

The MMR vaccine's effectiveness of 97% in preventing measles cases is a testament to the power of immunization. However, the prevention of measles in an unvaccinated population is a different matter. Measles will undoubtedly spread quickly in such a setting, as seen in the U.S. over the past decade. The importance of vaccination cannot be overstated, as it not only protects individuals but also helps maintain herd immunity and prevent the resurgence of this debilitating and sometimes deadly disease.

References:

Endemic or sustained measles transmission has not occurred in the United States since the late 1990s despite continued importations. During 2001--2008, a median of 56 range: 37--140 measles cases were reported to CDC annually. During the first 19 weeks of 2011, 118 cases of measles were reported, the highest number reported for this period since 1996.