Though federal health officials are moving ahead with a plan to produce 4.8 million doses of H5N1 avian influenza vaccine that targets the clade (strain) circulating globally and infecting US dairy herds and some farm workers, older H5N1 vaccines in the Strategic National Stockpile (SNS) might be useful in a pinch.
A team led by researchers from the US Food and Drug Administration looked at the ability of three H5N1 vaccines targeting three earlier H5N1 clades from Indonesia and Vietnam that circulated in the early 2000s to neutralize antibodies against the current 2.3.4.4b clade. All three are already licensed and are in the SNS. Two are adjuvanted, meaning they contain an immune-boosting substance.
The group published its unedited findings yesterday in Nature Communications to provide early access to the new information.
Newer vaccine still has some hoops to jump
At a media briefing this week, federal health officials said H5N1 vaccination isn't yet recommended for farm workers exposed to animals that carry the virus, but discussions remain ongoing. Their rationale is that infections are mild, and they have seen no changes to suggest the virus is more transmissible or is poised to cause more severe disease.
An official from the Department of Health and Human Services' Administration for Strategic Preparedness and Response said the fill-and-finish of a vaccine specific to the current clade from bulk candidate vaccine is still on track, with the first doses to be delivered in July. However, once produced, the vaccine would still need to go through regulatory approval before doses are used in people.
Earlier adjuvanted vaccines showed cross neutralization
In conducting the study, the team used blood samples from 68 adults who had participated in earlier H5N1 vaccine trials. The hemagglutinin (HA) sequence of the 2.3.4.4b H5N1 clade has several mutations compared to the HA of the three H5N1 viruses targeted by the earlier vaccines.
The researchers found that the two adjuvanted licensed H5N1 vaccines generated cross-reactive binding antibodies and cross-neutralization titers against the 2.3.4.4b clade.
"These findings suggest that the stockpiled U.S. licensed adjuvanted H5N1 vaccines generate cross-neutralizing antibodies against circulating HPAI H5N1 clade 2.3.4.4b in humans and may be useful as bridging vaccines until updated H5N1 vaccines become available," they wrote.
More H5N1 in cows, birds, small mammals
In other H5N1 developments, the US Department of Agriculture Animal and Plant Health Inspection Service (APHIS) added three more confirmations, all from Colorado, to its list of H5N1 outbreaks in dairy farms. The nation's total is now 161 outbreaks across 13 states.
APHIS also reported one more H5N1 detection in poultry, which involves a backyard flock of 30 birds in Idaho's Twin Falls County. It also reported 21 more detections in wild birds, several of which were agency-harvested birds in Sioux County, Iowa, where the virus has been detected in dairy herds. Other detections involved waterfowl and raptors found dead in other states, including California, Florida, and New York.
Meanwhile, APHIS reported H5N1 in samples from 11 more mammals, mostly house mice in New Mexico's Roosevelt County. They also included a red fox in New York's Tomkins County and a raccoon in Iowa's Sioux County.
