The outbreak of Type A of the H1N1 virus has killed 46 people in less than two months in Brazil. That is 10 times the figure for all of 2015, the Health Ministry said.
In Rio de Janeiro, which will host the Games from August 5-21, a first fatality was reported yesterday by health care authorities.
Through March 19, 305 cases were reported throughout the country, compared to 141 in all of 2015.
People have been waiting in line for more than three hours outside some hospitals to get vaccinated.
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In Brazil the H1N1 virus has normally appeared in recent years between May and July when temperatures are cooler.
But this year it has caught health authorities by surprise as it began in February.
It is not clear why, but many doctors say it stems from Brazilians who traveled to the northern hemisphere in the first months of the year.
The epidemic killed around 18,500 people in 214 countries. The alert was lifted in August 2010.
Since late 2015 Brazil has been at the epicenter of the Zika virus crisis. The virus has been blamed for birth defects in babies born of women infected with the virus, which is carried by mosquitos.