The emergence of a new “pox” virus is causing some confusion about chickenpox, monkeypox and smallpox. These viruses share similar rash symptoms, but differ with respect to infectiousness and severity of illness. Although the names sound similar, monkeypox is much harder to catch than chickenpox, and only chickenpox is prevented with routine immunization during childhood.
Chickenpox vaccination is recommended for children before school entry but the vaccine for monkeypox has only been used for those at high risk of occupational exposure—healthcare workers and those working with orthopoxviruses in a laboratory. Smallpox was declared eradicated by the World Health Organization in 1980 following a global vaccination program using the world’s first vaccine developed by Edward Jenner in 1796. The early vaccines were very primitive compared to today’s injections and had serious side effects. This is why vaccination programs weigh the risks and benefits of vaccination compared to the likelihood of infection and the seriousness of disease.
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What is the difference between chickenpox and monkeypox?
Chickenpox (varicella-zoster) was a common disease of childhood before the introduction of vaccines in 1995. The disease is caused by a herpesvirus and acquired the name varicella because the rash looks like a milder version of smallpox (variola). Smallpox and monkeypox, although they both cause a rash, belong to a different family of viruses—the orthopoxviruses.
Time from exposure to symptoms
One to two days before the chickenpox rash starts, people may feel tired, feverish, have a reduced appetite and a headache. Those who have been vaccinated may have fewer symptoms. Monkeypox may start with similar symptoms of a viral illness, but the rash may develop before other systemic symptoms, or not at all.
Both chickenpox and monkeypox cause a rash illness. The chickenpox rash usually appears on the scalp, face or trunk first, then spreads to the arms and legs. People who have been vaccinated against chickenpox may have mild breakthrough illness with few lesions. Monkeypox lesions are often found on the genitals, face, the oral mucosa (mouth and throat), hands, and as painful lesions in the anus, but the rash can also appear elsewhere on the body. Approximately 60% of people have had fewer than 10 lesions.
Chickenpox is highly infectious—if one person in the household is infected, between 61-100% of those who are not already immune will also become infected. Monkeypox secondary attack rates may range from 3% to 10% but further study during the current outbreak is warranted to generate a better estimate. Monkeypox is not as well-adapted to spreading between people as chickenpox.
Mode of transmission
The reservoir for chickenpox is humans while the reservoir for monkeypox—animals. Chickenpox is transmitted via droplets and respiratory secretions as well as contact with lesions. Monkeypox appears to be primarily transmitted by close personal contact and exposure to the lesions.
There are vaccines available for both viruses, but only the chickenpox vaccine is routinely given to children in a two-dose series. Like all herpesviruses, varicella lays dormant after the initial infection and can reactivate later in life to cause a painful rash called shingles. A shingles booster is recommended for adults over 50 years of age. The booster is highly effective in preventing shingles (>90%) among healthy adults and 68-91% effective in those with an immunocompromising condition. The monkeypox vaccine is also a two-dose series but is being reserved for those at high risk of exposure and those who have already been exposed.
Immunity from previous illness
Having recovered from chickenpox does not provide protection against monkeypox because the viruses are distinct.
Since the introduction of vaccines, the age-adjusted mortality rate for chickenpox has dropped substantially to 0.03 per million population. The mortality rate for monkeypox has historically been 3-6% according to the World Health Organization. The current outbreak is caused by the less virulent west African strain of monkeypox and appears to have a much lower mortality rate.
Other vaccine-preventable rash illnesses
Although rash illnesses can be very concerning, vaccines can prevent the most serious diseases of childhood. Measles is another highly contagious illness which was common in childhood before mass vaccination campaigns nearly eradicated it. Symptoms typically start with a cough, high fever, red, watery eyes and runny nose followed by a rash. Children younger than 5 and adults older than 20 years are more likely to have complications requiring hospitalization, such as pneumonia. This is a virus that is considered serious and parents are encouraged to contact their pediatrician if measles is suspected.
Today the US continues to see measles cases, typically among unvaccinated children. As more refugees from distressed countries find a new home here in the US, it is important to maintain protection against diseases that are more common elsewhere to keep community immunity high and disease circulation low. If your child has not yet had the measles/mumps/rubella (MMR) vaccine or the chickenpox vaccine, check with your local health department or pediatrician about getting up to date on vaccination.
Both the MMR and chickenpox vaccines are live, attenuated vaccines meaning they are weakened versions of the live viruses. This type of vaccine is highly effective at producing long-lasting immunity. Today, the incidence of chickenpox and measles is dramatically reduced making it unlikely that children will develop natural immunity at a young age when the illness is less severe. Children who are missing both chickenpox and MMR can receive a combination vaccine (MMRV). Adults without immunity can also be vaccinated.
The pandemic caused disruptions in healthcare for many families, making it more likely that once-rare diseases will become more common again. The best defense for children against measles, chickenpox and polio is routine pediatric immunization. Pediatricians are experts in vaccination and welcome parent questions about how to protect children against serious illnesses.