If you are a child of the 1950s you probably have an appreciation for Doo-Wop singing, B&W TV shows, and likely as not – still carry neutralizing antibodies against the H2N2 flu - which disappeared from humans when it was supplanted by the Hong Kong (H3N2) Flu of 1968.
Add in 50 to 60 years of accrued flu exposures, and a regular regimen of yearly flu vaccines, and you may well also be carrying cross-neutralizing antibodies to a variety of other potential pandemic flu subtypes. Subtypes – unlike H2N2 – you’ve never actually been exposed to.
At least that’s the conclusion of a study by NIAID researchers, recently published in the Journal of Infectious diseases. This is a phenomenon we’ve looked at previously (see JCI: Preexisting Human Antibodies Neutralize H7N9 influenza strains), and while certainly favorable news, high serum neutralization titers aren’t necessarily predictive of full immunity.
However, a history of repeated influenza exposures, along with repeated seasonal flu vaccinations might just provide an `edge’ against novel flu infection that someone with a more immunologically naive system might not have.
This comes from a relatively small study conducted on a very specific cohort, but the results are pretty impressive. While the full study is behind a pay we have the following abstract, after which I’ll return with a bit more.
Wei Wang1, Esmeralda Alvarado-Facundo1, Qiong Chen1, Christine M. Anderson2, Dorothy Scott2, Russell Vassell1 and Carol D. Weiss1
We examined serum samples from adults ages 48–64 who received multiple seasonal influenza vaccines from 2004 to 2009 for cross-neutralizing antibodies to potential pandemic strains.
Using pseudoviruses bearing various hemagglutinins (HA-pseudoviruses), we found serum neutralization titers (≥160) in 100% against A/Japan/305/1957 (H2N2), 53% against A/Hong Kong/1073/99 (H9N2), 56% against the H3N2 variant A/Indiana/08/11 (H3N2v), 11% against A/Hong Kong/G9/97 (H9N2), and 36% A/chicken/Hong Kong/SF4/01 (H6N1).
None had titers >160 to A/Shanghai/2/13 (H7N9) or A/Netherlands/219/03 (H7N7).
Thirty-six percent to 0% had neutralization titers to various H5N1 strains. Titers to H9, H6, and H5 HA-pseudoviruses correlated with each other, but not with H3N2v, suggesting group-specific cross-neutralization.
While we watch all of these subtypes (and more) for possible pandemic development, the H2N2 virus has a history of producing a pandemic in recent years (1957), and variants of that subtype continue to circulate in avian hosts.
In 2013, in H2N2: What Went Around, Could Come Around Again, we looked at a study from St. Jude Children’s Hospital researchers who warned that this 1950s pandemic influenza virus remains a potential health threat, particularly to those under 50.
In 1977 with the return of H1N1 (aka `Russian flu’), and again in 2009 with the H1N1 pandemic flu, those born before 1957’s pandemic saw lower levels of infection, as they had been around when H1N1 was still circulating as a seasonal virus.
It is possible, based on these findings, that should H2N2 return as a pandemic virus in the next couple of decades, those born before 1968 could enjoy similar levels of immunity.
And, as happened in both 1977 and 2009, having a large segment of the population already with some degree of immunity could help lessen its overall impact.