The measles virus is making a resurgence in the United States despite the long-standing availability of a vaccine that provides nearly lifelong immunity. In recent weeks, hundreds of people were exposed a child with the virus at a Northern California health care facility; Our state is one of 17 jurisdictions with reported measles cases in 2024higher than that observed in recent years.
Measles is an extremely transmissible pathogen: on average, an infected person infects 12 to 18 unvaccinated people. The airborne virus can linger in floating aerosols long after someone has left a room, and common symptoms, including a rash, high fever, watery eyes, cough and runny nose, typically take a week or two to appear. .
Infections can also cause immune amnesia, in which your immune system gets better at fighting measles and worse at fighting other infections that it was previously protected against. In rare cases also leads to deathmore often in children than adults, from respiratory or neurological complications, including a type of brain inflammation in young children that can appear years after the initial measles infection.
Before the measles vaccine was introduced and licensed in 1963, the The Centers for Disease Control and Prevention cites an annual average of 549,000 cases (and probably millions more go unreported), 48,000 hospitalizations, almost 500 deaths and 1,000 people with chronic disabilities. In 2000, thanks to vaccination, measles was declared eliminated in the United States. But due to cases of people arriving here from other countries, combined with pockets of low vaccination, we are seeing outbreaks among unvaccinated people.
Politics can make the problem worse. Last month in Florida, following an outbreak at an elementary school, the state's surgeon general left the decision to the parents whether to send their children to school, citing high levels of community immunity as the reason for not following the usual protocols. That arrogant response risked a much worse outbreak. A more standard response would have required unvaccinated students and staff to be vaccinated and quarantined for 21 days (the period of time in which the disease could develop).
It might be tempting for Californians to dismiss this as a Florida problem. But our state has a time bomb against measles. Ideally, communities should reach at least 95% vaccination to achieve herd immunity. But a recent national survey found that southeastern california In that country alone there are 350 schools that do not meet the desired vaccination threshold, meaning that a single case of measles in these schools could easily become an outbreak among the unvaccinated.
Misinformation about the measles vaccine has been a problem for years. TO discredited But an influential 1998 research paper published in the Lancet, a British medical journal, suggested a link between the vaccine, which babies can receive as young as 12 months old, and autism. The article was retracted in 2010 (and the authors were later reported to have committed fraud). But measles vaccine rates fell in England throughout the early 2000s.
In California, a 2014 Outbreak at Disneyland was connected to more than 140 cases in North America, with declining vaccination rates being a contributing factor. A recent systematic review of the reasons why parents refuse the measles vaccine for their children found fear of autism the most cited concern. Those who were hesitant more frequently cited the Internet and social media as sources of information about vaccines than those who were not hesitant.
In recent years, hesitancy has increased as misinformation about the COVID vaccine has caused some parents to doubt routine inoculations. Vaccination exemptions during the 2022-23 school year reached highest level ever reported in the US, increasing in 40 states and Washington, DC, and 10 states reaching exemption rates above 5%. According to the CDC, the 93.1% vaccination rate among eligible children puts about 250,000 kindergarten students at risk of contracting measles.
It is encouraging that we have seen in our own state that vaccine hesitancy can be reversed. Marin County had among the lowest Measles vaccination rates in the state in 2011 and now coverage. about 99% among children entering school. State contact tracing efforts that were strengthened during COVID-19, including California connected program, have been useful in tracing contacts of measles cases.
But, as recent scares remind us, we are not yet where we need to be with vaccination. Following the Disneyland outbreak, California passed a law in 2015 to eliminate the “personal beliefs” exemption from required childhood vaccines, meaning people must provide a medical reason to refuse it. The law expanded the criteria for medical exemptions, which increased the year after their approval. Although the state strengthened medical exemptions with a new law In 2019, when the pandemic disrupted routine vaccinations and increased homeschooling, the percentage of kindergarteners who were not up to date on vaccinations increased in 2021.
Vaccine Exemption Laws vary widely in the US.Some states only allow medical exemptions, some also allow religious exemptions, and others allow philosophical exemptions also. And outbreaks in one state can spread quickly across borders.
That means decisions by Florida's public health department and vaccine hesitancy anywhere can affect us all. California needs to close the gap for communities that are not well protected against measles.
Abraar Karan is a physician and infectious diseases researcher at Stanford University, where Julie Parsonnet is a professor of infectious diseases and of epidemiology and population health.
