In the US, several contacts of the recent human H5N1 case in Missouri that was discovered through routine hospital influenza surveillance reportedly developed symptoms of respiratory infections around the same time. A household contact developed similar symptoms on the same day as the hospitalized patient and has since recovered. In addition, two healthcare workers developed symptoms. One developed mild symptoms and tested negative for flu, and the other developed mild respiratory symptoms but was not tested. Further tests will look for antibodies to H5N1 in these patients; blood for such serology tests have been collected from the hospitalized patient and the household contact, and serology testing has been offered to the healthcare worker who was not tested for flu.
Also, the virus isolated from the hospitalized patient was found to have several mutations, one of which would likely drastically reduce the efficacy of an H5N1 vaccine that would be made using the current candidate vaccine strain.
This potential cluster of human H5N1 cases is concerning. It is likely - but not certain - that the hospitalized patient and the household contact were both infected with H5N1 by another, unknown person, because they developed symptoms on the same day. If this did occur, then it raises several questions. How many other people did that unknown person infect? More generally, how big is the human-to-human transmission cluster that has been discovered here? Is any human-to-human transmission chain in this cluster ongoing? It will also be good to know whether it was likely that the hospitalized patient transmitted H5N1 to either healthcare worker who was sick.
It is not likely that H5N1 influenza is spreading widely in humans at this time, because we would see that in wastewater data and, more importantly, in routine influenza testing. What has likely been detected here is almost certainly a small, self-limited cluster of human-to-human transmission. However, it is also possible that there is still an ongoing human-to-human chain of transmission that is affecting a very small number of people and remains undetected. And the longer that chain of transmission is, the higher the probability that the virus will adapt successfully to humans.
For H5N1, one forecaster elaborates:
In the US, several contacts of the recent human H5N1 case in Missouri that was discovered through routine hospital influenza surveillance reportedly developed symptoms of respiratory infections around the same time. A household contact developed similar symptoms on the same day as the hospitalized patient and has since recovered. In addition, two healthcare workers developed symptoms. One developed mild symptoms and tested negative for flu, and the other developed mild respiratory symptoms but was not tested. Further tests will look for antibodies to H5N1 in these patients; blood for such serology tests have been collected from the hospitalized patient and the household contact, and serology testing has been offered to the healthcare worker who was not tested for flu.
Also, the virus isolated from the hospitalized patient was found to have several mutations, one of which would likely drastically reduce the efficacy of an H5N1 vaccine that would be made using the current candidate vaccine strain.
This potential cluster of human H5N1 cases is concerning. It is likely - but not certain - that the hospitalized patient and the household contact were both infected with H5N1 by another, unknown person, because they developed symptoms on the same day. If this did occur, then it raises several questions. How many other people did that unknown person infect? More generally, how big is the human-to-human transmission cluster that has been discovered here? Is any human-to-human transmission chain in this cluster ongoing? It will also be good to know whether it was likely that the hospitalized patient transmitted H5N1 to either healthcare worker who was sick.
It is not likely that H5N1 influenza is spreading widely in humans at this time, because we would see that in wastewater data and, more importantly, in routine influenza testing. What has likely been detected here is almost certainly a small, self-limited cluster of human-to-human transmission. However, it is also possible that there is still an ongoing human-to-human chain of transmission that is affecting a very small number of people and remains undetected. And the longer that chain of transmission is, the higher the probability that the virus will adapt successfully to humans.