The immune system protects us from viruses and bacteria. People without a properly working immune system are more likely to die of both. Some people are born with defective immune systems (Severe Combined Immunodeficiency) while others acquire a malfunctioning immune system as a result of viral infection (HIV/AIDs).
A recent report in Clinical Infectious Diseases by Gordon et al., suggests that pandemic H1N1 is associated with deficiency of one part of our immune response, immunoglobulin G2 (IgG2):
Patients with severe H1N1 infection were signiﬁcantly more likely to be deﬁcient in IgG2 than were patients with moderate H1N1 infection (P = .001 ); IgG2 deﬁciency was not necessarily noticeable if only total IgG levels were assessed. Furthermore, our ﬁndings suggest that, for the majority of such patients (11 of 15 patients; 73%), IgG2 deﬁciency persists after recovery from H1N1 infection, regardless of whether the illness was associated with possible risk factors, such as pregnancy. Low IgG2 levels are therefore less likely to be simply related to a severe inﬂammatory response, as is sometimes noted for acute-phase reactants, such as albumin, creatine kinase, and lactate dehydrogenase [8, 11].
These findings raise an important question – did patients with severe H1N1 symptoms have a preexisting deficiency in their immune system or did H1N1 itself cause the deficiency?
At this point, there is insufficient evidence to say. From the paper:
…it is uncertain whether we have simply identiﬁed a cohort of patients with H1N1 infection with underlying unrecognized IgG2 deﬁciency, or whether there is an interaction between the H1N1 virus and the host that leads to such deﬁciency.
Apparently healthy individuals can have low levels of IgG (2-20%). However, if this is the group of people who experience more severe symptoms with the new H1N1, then it may be worth identifying this subgroup and making sure that they and their physicians are warned about their elevated risk for severe symptoms with the new H1N1 virus.
If the H1N1 virus is causing IgG2 deficiency, this is not a temporary effect. From the paper:
… the fact that the IgG2 deﬁciency that we identiﬁed appears to persist in most cases long after disease resolution … suggests the possibility of potential long-term implications for these patients and that follow-up of moderate and severe cases of H1N1 infection may be warranted.
The possibility of another virus (other than HIV) that causes permanent damage to the immune system is disturbing. If this is the case, there will be deaths due to pandemic H1N1 long after the pandemic is declared over.
Gordon et al. (2010) Association between Severe Pandemic 2009 Inﬂuenza A (H1N1) Virus Infection and Immunoglobulin G2 Subclass Deﬁciency. Clinical Infectious Diseases.