The World Health Organization (WHO) today announced the flu vaccine strain recommendations from its advisory group for the Northern Hemisphere 2024-25 flu season, which are the same as the group recommended for the Southern Hemisphere's 2024 season.

As for its recommendation for the Southern Hemisphere seasonal flu vaccines in September, the WHO experts recommends that companies switch back to trivalent (three-strain) vaccines and leave out the influenza B Yamagata lineage component.

Yamagata B lineage not detected since 2020

In accompanying background information, the WHO said no naturally occurring influenza B Yamagata lineage viruses have been confirmed since March 2020 and that the vaccine strain isn't needed anymore.

The recommendations for egg-based and cell-based vaccine strains vary, and the latest picks for both versions of the Northern Hemisphere vaccines are the same those recommended for the Southern Hemisphere.

For countries that still use quadrivalent (four-strain) versions of the vaccine containing a second B strain, the WHO recommends a strain similar to the Yamagata Phuket/3073/2013 lineage virus, the same as other recent picks.

Advisers pick 2 new pandemic preparedness vaccine viruses

During their twice-a-year meetings to recommend strains to include in seasonal flu vaccines, the WHO's advisory group also examines the latest developments with zoonotic flu strains to see if any new viruses are different enough from earlier strains to warrant new candidate vaccine strains for pandemic preparedness.

At its meeting, the group proposed two new candidate strains, both targeting recent variant H1N1 viruses. One is antigenically similar to A/Catalonia/NSAV198289092/2023, and the other is similar to A/England/234600203/2023.

Data across nine pre-COVID flu seasons in Ontario reveal that flu vaccine effectiveness (VE) wanes 9% every 28 days beginning 41 days post-vaccination in adults but not in children, according to a study yesterday in Eurosurveillance.

The researchers, a group called the Canadian Immunization Research Network (CIRN) Provincial Collaborative Network (PCN) Investigators, analyzed data from lab and health administration databases in the province from the 2010-11 through the 2018-19 flu seasons. Participants were Ontarians 6 months and older living in the community who received a flu vaccine before being tested for influenza using polymerase chain reaction tests.

Of 53,065 people who were vaccinated before testing, 10,264 (19%) tested positive for flu.

The investigators determined that the odds of contracting influenza increased from 1.05 (95% confidence interval [CI], 0.91 to 1.22) at 42 to 69 days after vaccination, and peaked at 1.27 (95% CI, 1.04 to 1.55) at 126 to 153 days compared with the reference interval, which was 14 to 41 days after vaccination. This corresponds to a 5% to 27% drop in VE compared with shortly after vaccination.

No waning protection found in kids

The researchers also determined that VE dropped 9% every 28 days—or a 1.09-times increased risk of influenza every 28 days (adjusted odds ratio [aOR], 1.09; 95% CI, 1.04 to 1.15). They did not, however, observe any VE waning in children.

Adults 18 to 64 years showed the greatest decline in protection against the H1N1 strain (aOR per 28 days, 1.26; 95% CI, 0.97 to 1.64). For people 65 years and older, it was against the H3N2 strain (aOR per 28 days, 1.20; 95% CI, 1.08 to 1.33).

Annual influenza vaccination programmes need to strike the balance between vaccinating the population too early versus too late.

The authors conclude, "Annual influenza vaccination programmes need to strike the balance between vaccinating the population too early versus too late, while taking into account system vaccination capacity and year-to-year variability of influenza season timing." They add, "Certain age groups may experience more pronounced waning of the protection against specific influenza types/subtypes."

The Arkansas Game and Fish Commission (AGFC) yesterday confirmed that a hunter-harvested white-tailed deer in Craighead County tested positive for chronic wasting disease (CWD), an always-fatal prion disease.

The 2-year-old doe was harvested near Jonesboro during the Arkansas firearm season late last year. A sample from the doe tested positive for CWD, and the finding was confirmed by the Wisconsin Veterinary Diagnostic Laboratory in Madison.

Craighead County is in northeastern Arkansas, abutting Missouri and not far from the Tennessee border.

Expanded CWD management zone

The AGFC noted that, in addition to Craighead County, three new counties—Sharp, Cleburne, and Mississippi—have been added to the CWD management zone owing to their proximity to other newly identified CWD positive cases. "This proactive measure of including counties based on risk values is outlined in the state's CWD Management and Response Plan," the AGFC said.

Cory Gray, chief of the AGFC's Research Division, said, "Protecting the health of Arkansas's deer herd is our top priority. We are being very proactive in all of our CWD management areas."

Protecting the health of Arkansas's deer herd is our top priority.

CWD is a neurologic disease that leads to animals' deteriorating physical condition, including wasting, in deer, elk, caribou and moose. Officials first detected it in Arkansas in February 2016. Since then, the AGFC has tested more than 40,670 deer and elk for CWD, and 1,260 deer and 38 elk—or about 3% of all animals tested—have tested positive for the disease.

Children born in October and vaccinated against influenza in that month are both more likely to be vaccinated against flu and less likely to be diagnosed as having influenza than children born in other months, according to a new study The BMJ.

The observational study is based on insurance records of 800,000 US children ages 2 to 5 years old who received flu vaccines from 2011 to 2018. Researchers analyzed rates of diagnosed influenza among children by birth month, and found that those with October birthdays had the lowest rates.

US children typically visit pediatricians around their birthday each year for well-check visits and routine vaccinations, and children who visit in October were likely offered the seasonal flu shot as it was available. The seasonal shot would not likely be ready for children with spring and summer birthdays, the authors said.

October flu vaccinations were greater in children with October births compared with other birth months, with 48.9% of children born in October were vaccinated in October, compared with 34.0% of children born in August, 40.2% of those born in September, 27.3% of those born in November, and 33.7% of those born in December.

October may be best month to get flu shot

The authors found that 2.7% of children born and vaccinated in October were diagnosed as having flu that season. The percentage rose to 3.0% of those born and vaccinated in August or January, 2.9% of those born and vaccinated in September or December, and 2.8% of those born and vaccinated in November.

This suggests October maybe the optimal time to be vaccinated against the flu.

"Under the assumption that children born in October are otherwise similar to children born in other months, our findings suggest that the specific timing of influenza vaccination among children born in October may lead to lower rates of influenza infection," the authors concluded.

In a Harvard Medical School press release on the findings, senior study author Anupam Jena, MD, PhD, said, "There are a lot of variables when it comes to the timing and severity of flu season or a person’s risk of getting sick, and many of those are out of our control. One thing we have some control over is the timing of the shot, and it looks like October is indeed the best month for kids to get vaccinated against the flu."