Low CD4 cell count associated with poor response to swine flu vaccine for those with HIV

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Many HIV-positive patients do not develop protective antibody levels after receiving the standard dose of the swine flu vaccine, a study published in the September 10th edition of AIDS shows. A low current CD4 cell count was the only factor associated with a poor response to the vaccine.

“The implications of this research are immediate for next year’s influenza vaccination campaign”, comment the investigators. “Our results suggest that if that vaccine is used at the currently recommended dose, a significant proportion of individuals will remain vulnerable to influenza”.

It is recommended that all HIV-positive patients should receive the seasonal flu vaccine. In 2009 the H1N1 (swine flu) virus was identified and the World Health Organization declared a global flu pandemic. A vaccine against the virus was developed and people with underlying health conditions – including HIV - were recommended to receive this.



Lowest of a series of measurements. For example, an individual’s CD4 nadir is their lowest ever measured CD4 count.


A laboratory measurement of the amount, or concentration, of a given component in solution.


response rate

The proportion of people asked to complete a survey who do so; or the proportion of people whose health improves following treatment.


Injected into a muscle.

immune system

The body's mechanisms for fighting infections and eradicating dysfunctional cells.

The vaccine is provided via a single intramuscular injection, the standard dose being 15 µg. The production of an antibody titre of at least 1: 40 on the hemagglutination-inhibition (HAI) assay is considered protective against the virus.

Investigators from the University of Pennsylvania wished to see if the vaccine produced protective antibody levels in HIV-positive patients. The safety of the vaccine was also monitored.

Their study sample included 120 patients who received the vaccine in November and December 2009. Most (71%) were men, 68% were African American, and their median age was 46.

All but one of the patients was taking antiretroviral therapy, and the current median CD4 cell count was 502 cells/mm3. The median nadir CD4 cell count was 132 cells/mm3. The majority (92%) had a viral load below 400 copies/ml.

Monitoring at the time of vaccination showed that a quarter of patients had already been exposed to swine flu and had protective antibodies against the infection.

However, of the 90 patients without pre-exposure to the virus, only 61% had protective levels of antibodies three weeks after receipt of the vaccination.

Non-responders had low current (394 vs 497 cells/mm3) and nadir (112 vs 153 cells/mm3) CD4 cell counts and had had an undetectable viral load for a shorter period of time (19 vs. 28 months) than responders.

Statistical analysis showed that the only factor significantly associated with a poor response to the vaccine was a lower current CD4 cell count (p = 0.019).

The vaccine was safe, the most common side-effect being a localised, injection site reaction. This developed in 18% of patients.

“Up to 40% of HIV-positive individuals are not seroprotected after vaccination”, write the investigators.

“The presence of other underlying chronic diseases, medication use, poor nutrition, irreversible damage to the immune system and immunosenescence [decline of the immune system due to ageing], likely all play a role in decreased vaccine responsiveness in spite of successful treatment of the HIV infection”, they add.

A number of strategies are suggested by the researchers to enhance the response rate to the vaccination. These include the use of alternative vaccines; increasing the dose; the use of adjuvants; and the use of live vaccines.

The authors of an accompanying editorial note the findings of the study, emphasising “suboptimal vaccine efficacy in HIV-infected persons represents a clinically important matter. Current evidence evaluating influenza vaccination efficacy in the HIV population remains insufficient”.


Tebas P et al. Poor immunogenicity of the H1N1 209 vaccine in well controlled HIV-infected individuals. AIDS 24: 2187-92, 2010.

Reyes-Teran et al. Preventing influenza coinfection among HIV-infected persons: a complex picture coming into focus. AIDS 24: 2283-85, 2010.