Cannabis made vaccinia virus infections worse in mice by suppressing immune function

What the researchers found

Researchers found that a single dose of cannabis resin was equally effective as pure THC at increasing the severity and duration of vaccinia virus (smallpox vaccine virus) infection in mice.

In vitro, cannabis resin was more potent than THC alone at inhibiting immune cell proliferation, suggesting additional cannabis compounds beyond THC contributed to immunosuppression. Sub-fractions containing cannabidiol and cannabinol (also found in cigarette smoke) were also inhibitory.

The immunosuppressive effects were distinct from direct cell-killing (apoptotic) effects, as drug-treated immune cells retained their ability to produce cytokines when stimulated.

The authors noted a recent case of unusually severe cowpox infection in a young drug user, and concluded that cannabis could increase risk of acquiring poxvirus infections or experiencing worse vaccine side effects.

Why it matters

The finding that cannabis enhanced viral infection severity had implications for immunocompromised individuals and vaccination programs, suggesting cannabis users might face increased infection risks.

The numbers in context

Single dose of cannabis resin or THC enhanced vaccinia symptoms. Cannabis resin was superior to THC alone at inhibiting immune cell proliferation in vitro. CBD and CBN fractions also showed inhibitory effects.

How the study worked

Animal study and in vitro experiments. Mice infected with vaccinia virus after cannabis resin or THC administration. In vitro immune cell proliferation assays with human and mouse spleen cells and PBMCs. Sub-fractionation of cannabis resin to identify active components.

What this study cannot tell us

Mouse model with vaccinia virus, which has limited relevance to most modern infections. Single-dose exposure protocol. In vitro immune effects may not fully translate to in vivo immune function.

How to read the evidence

Animal and in vitro study with mechanistic component identification but limited clinical relevance of the vaccinia model.

When this study was published

Published in 2011. Cannabis immunology research has continued with more clinically relevant infection models.

The bigger picture

This study added to evidence that cannabis has meaningful immunosuppressive effects that could have real clinical consequences, particularly for susceptibility to viral infections.

Questions still open

• Do cannabis users have increased susceptibility to common viral infections? Should vaccination protocols consider cannabis use status?

Common questions

Read the original research

Cannabinoids lead to enhanced virulence of the smallpox vaccine (vaccinia) virus.

Immunobiology, 216(6), 670-7

Citation

Huemer, Hartwig P; Lassnig, Caroline; Bernhard, David; Sturm, Sonja; Nowotny, Norbert; Kitchen, Maria; Pavlic, Marion. (2011). Cannabinoids lead to enhanced virulence of the smallpox vaccine (vaccinia) virus.. Immunobiology, 216(6), 670-7. https://doi.org/10.1016/j.imbio.2010.11.001

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