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Measles outbreak in Samoa: potential effects of immune amnesia on the impact of COVID-19

Measles outbreak in Samoa: potential effects of immune amnesia on the impact of COVID-19

Measles—one of the world’s most contagious diseases—induces immune amnesia, an anomaly of the immune system that results in increased susceptibility to infections by other pathogens. Not surprisingly, there are concerns globally about populations that have recently experienced measles outbreaks. These populations could be at elevated risk of developing more severe COVID-19 illness, resulting in increased mortality.    The emergence of the current COVID-19 pandemic in the first months of 2020 occurred closely after a global resurgence of measles. According to the World Health Organization (WHO), by November 2019, measles case numbers had tripled compared with the same period in the previous year. Measles spreads easily when an infected person coughs or sneezes and, before a vaccine became widely available in the 1960s, it caused millions of deaths worldwide annually. It is estimated that between the years 2000-2018, vaccination against measles alone saved around 23 million lives. However, measles outbreaks occurred in the past few years in all regions of the world and in many countries—from the Democratic Republic of Congo (DRC), to Samoa and Ukraine. These outbreaks, along with inadequate immunization rates, threaten to derail the crucial gains obtained in the two past decades. Measles virus, courtesy of the Centers for Disease Control and Prevention Last year, in Samoa—a small island country in the central South Pacific Ocean—an unprecedented measles outbreak overwhelmed the nation’s health infrastructure, with hospitals at about 300% past capacity. Before the outbreak began, vaccination rates—already lower than the approximately 95 percent required for herd immunity—had plunged to 31%. The first case of measles was confirmed in September 2019 and, on November 15, the government declared a state of emergency. Up to 3% of the population became infected, and 87 people died, mostly very young. The state of emergency was lifted in December 2019. However, measles may have long-term consequences. Even after recovery, immune amnesia can persist for over 2 years. Results from a study published a few days ago indicate that, in Samoa, immune amnesia may result in more severe cases of COVID-19. To model the morbidity and mortality impact of a potential COVID-19 epidemic in the country, researchers used data from the WHO situation reports of the measles epidemic in Samoa, and assumed that immune amnesia would be present in children infected from November 2019 onward for at least 12 months and up to 36 months.   They found that immune amnesia could increase the total number of COVID-19 cases by 8% and deaths by more than 2%. The highest rate of death would be in people older than 60 years, but a smaller peak in death could occur in younger people, with more than 15% of total deaths in the...

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