Meta-analysis finds no protection drop-off with consecutive flu vaccination
A new meta-analysis of 42 flu studies found that vaccination over two consecutive seasons didn't reduce flu vaccine effectiveness (VE) compared with people vaccinated during the current season, but the researchers included the caveat that the overall quality of evidence was low, due to inconsistency and imprecision among the studies. A team based at McMaster University in Canada reported its findings yesterday in Vaccine.
Of the 42 studies that met the group's inclusion criteria, 5 were randomized controlled trials (RCTs) and 39 were observational studies. The studies covered 23 flu seasons, from 1983-84 to the middle of the 2016-17 season. In the 5 RCTs, which had 11,987 participants, VE for those vaccinated over two consecutive seasons was 71% (95% confidence interval [CI], 62% to 78%), compared with 58% in those vaccinated in the current season (95% CI, 48% to 66%). The team saw a similar pattern for the observational studies, which had 28,627 participants.
Subgroup analysis also supported the findings, but a dose-response analysis did show a reduced effectiveness in those who had three or more consecutive vaccinations.
Overall, the researchers said the findings were generally consistent with previously reported studies. In noting that the findings don't rule out the possibility of reduced effectiveness, the investigators said that reporting vaccine history using the exact number of doses and composition across multiple prior years in future observational studies could help tease out the biological mechanism behind the impact of two or more consecutive vaccinations.
"Furthermore, it is critical that assessment and reporting of antigenic drift and vaccine match be improved in future studies," they wrote.
May 1 Vaccine abstract
Countries report sporadic detections of H5N6, H5N8, H5N2 avian flu
Over the past week, four countries reported new highly pathogenic avian flu detections involving different strains, according to the latest notifications from the World Organization for Animal Health (OIE).
Outbreaks in Germany and Japan involved H5N6 in wild birds. In Germany, veterinary officials reported the virus in a white stork found dead on Apr 28 in Lower Saxony state in the country's northwest. The last German H5N6 outbreak occurred in the middle of March in backyard birds in Schleswig-Holstein state. In Japan, the virus was found in two large-billed crows found dead on Mar 18 and Mar 25 in the city of Itami in Hyogo prefecture. The virus was linked to crow deaths that occurred in early March in the same city.
Elsewhere, Saudi Arabia reported seven more H5N8 outbreaks in poultry that started from Feb 20 to Mar 30 at different farms in Riyadh province. The virus killed 11,336 of 3,022,731 susceptible birds among the seven outbreaks, and authorities culled the remaining poultry to control the spread of the virus. Saudi Arabia has reported a small but steady stream of H5N8 outbreaks since the end of 2017.
In Taiwan, the agriculture ministry reported two more H5N2 outbreaks on commercial poultry farms. One began at a duck farm in Pingtung County on Apr 17 and the other started at a goose farm in Yunlin County on Apr 20. Taken together, the virus killed 545 of 6,204 birds, and the remaining poultry were culled as part of the outbreak response.
Apr 30 OIE report on H5N6 in Germany
Apr 27 OIE report on H5N6 in Japan
May 1 OIE report on H5N8 in Saudi Arabia
May 1 OIE report on H5N2 in Taiwan