In April the WHO warned that measles cases had increased by 79% in the first two months of 2022. The countries with the highest reported number of cases were in Africa and East Mediterranean. As the year has progressed cases have continued to increase as a consequence of delayed vaccination campaigns due to the COVID-19 pandemic and vaccine hesitancy and resistance in some communities. Optimizing measles vaccine coverage is a key priority in reducing the disease burden from this vaccine preventable diseases.
Measles is an ancient infectious disease thought to have appeared in humans in the 6th century BCE. It likely emerged from a cattle disease ( the ancestral relative of rinderpest virus) and crossed into humans as humans domesticated livestock and populations coalesced around cities with increasing trade and travel. Humans are the only natural hosts though monkeys can get infected. Measles is a highly contagious respiratory virus, with a high transmission rate; an infected individual can result in as many as 12-18 secondary infections.
Measles is an RNA virus and a member of the paramyxovirus family. Other members of this virus family include the mumps virus, parainfluenza virus and RSV. The measles virus has six structural proteins, among them is an attachment and a fusion protein. The virus enters the host in stealth mode, quietly binding to receptors on epithelial cells and spreading from the respiratory tract through to the body’s lymphatic system. In the lymphatic system it binds to receptors on immune cells weakening them and leading to the immunosuppressive effects of the virus. The virus amplifies and reaches peak virus load prior to the onset of symptoms. Symptoms typically occur 10-14 days after infection. The virus replicates in various tissues such as in the mouth, the throat, and the skin. The infection has a prolonged period of contagiousness, and the virus can be detected for several months after the rash has gone.
The classic symptoms of measles are cough, coryza, conjunctivitis. White spots on a reddened base can be seen in the mouth and often occur a couple of days before the rash. Early symptoms are similar to those of other viral illnesses until the oral lesions and rash develop. Measles hepatitis can also occurs. The virus targets immune cells, affecting their function and leading to several complications including pneumonia, and other secondary bacterial or viral infections. An infection of the heart known as myocarditis can also occur. The virus can also cause three different rare, but severe types of central nervous system disorders known as encephalitis. One type of measles associated encephalitis can occur years after the initial infection especially in children infected with measles very early in life. Vaccination is effective at preventing this complication. Malnutrition and in particular vitamin A deficiency is associated with more severe outcomes. Complications such as encephalitis are more common in children with vitamin A deficiency.
Vaccines against measles are attenuated whole virus vaccines. Prior to the availability of vaccines, epidemics would occur every 2-5 years with over 2 million deaths each year. During a measles outbreak in 1954, John Enders and his team isolated a measles strain that they weakened through serial passaging making this strain the basis of a measles vaccine. Enders was a pioneering Harvard virologist whose work contributed to vaccine development for measles, polio and mumps. The first measles vaccines were licensed in 1963.
Today the WHO recommends two doses of measles vaccines. In most countries the first dose can be given between 9-12 months, and the second dose between 15-18 months. In countries with low levels of transmission and high first dose coverage, such as the United States the first dose is usually administered at 12 months and the second dose can be delayed till school entry (ages 4-6 years). But, every opportunity should be taken to vaccinate against measles for anyone who has missed a measles dose. A supplementary measles dose can be given to infants from 6-months of age in the setting of a measles outbreak, and to infants who are refugees, living in conflict zones or those that are HIV infected or HIV exposed. Children who receive this supplementary dose should also receive the recommended two doses at the prescribed ages based on the country’s vaccination schedule. The vaccines are highly effective and convey immunity to 97% of those that receive two doses.
In 2018 they were 350,000 measles cases globally and 142,000 deaths. Reductions in Global vaccination rates have played an important role in increasing global cases and deaths from measles. Vaccination coverage needs to be as high as 93-95% in order to achieve herd immunity, but global vaccination coverage rates remain low. At the end of 2021 global first dose coverage rates were 81%, while second dose coverage rates are 71%. In Africa those numbers are 68% and 41% for first and second dose coverage.
Low rates of vaccination coverage have led to several outbreaks. The United States declared itself free from measles in 2000 with sporadic cases typically in unvaccinated individuals and sometimes linked to an imported case. In 2019 the United States experienced the largest outbreak since 1992, with over 1200 cases. The vast majority occurred in unvaccinated individuals often in close knit under vaccinated communities. Further spread can be effectively curbed by having high rates of population immunity and implementation of supplementary vaccination campaigns. Several countries including Nigeria, India, Liberia, Pakistan, Ethiopia, Afghanistan, DRC, Cameroon have reported measles outbreaks in 2022. Zimbabwe is currently experiencing an outbreak with almost 7000 reported cases and 700 deaths. Most of these are in areas with low levels of vaccination, among close knit communities, often following mass gatherings that also contribute to dispersal of cases across the country.
Measles is not only a public health crisis, but like so may infectious diseases can affect the lives and livelihoods of infected and affected individuals. Measles cases can have a significant economic burden on individual households impacting household financial security due to financing of healthcare costs or lost caregiver income. The poor are disproportionately affected. The resurgence of vaccine preventable infections such as measles in some of the poorest countries and communities exacerbates health inequality.
The current rise in vaccine preventable diseases further highlights the need to tackle the 3Cs of vaccine hesitancy - confidence, convenience, and complacency. Building trust in communities is essential. Providing health information and addressing people’s concerns about safety and effectiveness through non-judgmental engagement should be a key component of any public health vaccination strategy. Making vaccination convenient, affordable, and accessible should be a priority. As we all become increasingly removed from the personal experience with the complications associated with diseases such as measles or polio it is important to tackle complacency through accurate health information that counteracts pervasive vaccine misinformation. Measles vaccines save lives. As we all try to return to post-pandemic normalcy (although the pandemic is not over) let us all work together in all of our communities to curb the rise in cases of vaccine preventable infections such as measles.