New cholera vaccine is effective among people with HIV

A new, orally administered cholera vaccine has been shown to be effective against clinically significant cholera in an urban sub-Saharan population with a high prevalence of HIV infection.

The results offer one of the best possibilities for improved control of cholera, even among HIV infected people, who may not respond well to other cholera vaccines.

The results come from an evaluation in Beira, Mozambique—a city where the seroprevalence of HIV is 20% to 30%—of a mass immunisation programme with an oral cholera vaccine consisting of recombinant cholera toxin B subunit and killed whole cells (the rBS-WC vaccine) (New England Journal of Medicine 2005;352:757-67). The World Health Organization recently recommended that this and other new generation cholera vaccines be considered in certain areas. However, it said that demonstration projects were needed to provide information about the costs, feasibility, and effectiveness of the vaccines.

The rBS-WC vaccine and its predecessor, the BS-WC vaccine, which contained chemically extracted rather than recombinant cholera toxin B subunit, have already been shown in studies to be safe and protective. Previous trials were conducted in settings where cholera is endemic but without a high prevalence of HIV infection (Lancet 1990;335:270-3).

In the new evaluation, conducted from December 2003 to January 2004, investigators led by Marcelino E S Lucas from the Mozambique Ministry of Health undertook mass immunisation of adults (excluding pregnant women) and children who were at least 2 years old, in Beira's Esturro district (population 21 818). They used a two dose regimen of rBS-WC vaccine.

The researchers then assessed vaccine protection in a case control study during an outbreak of El Tor Ogawa strain of cholera in Beira between January and May 2004. To estimate the level of protection conferred by the vaccine the researchers compared the rates of previous vaccination in people with cholera confirmed by culture with control patients from the district without diarrhoea, matched by age and sex. They evaluated the effectiveness of the vaccine in 43 people with cholera and 172 controls. They found that, in people who received one or more doses of rBS-WC, the vaccine resulted in 78% protection against cholera infection (95% confidence interval 39% to 92%; P=0.004). The degree of protection in people aged over 15 (an age group in which rates of HIV coinfection may be as high as that among pregnant women in Beira) was similar to that in children aged younger than five years.

A concurrent case-control study, conducted to detect bias, compared people with treated, non-choleraic diarrhoea and controls without diarrhoea in the same population. It found that the rBS-WC vaccine offered no protection against non-choleraic diarrhoea.

In an accompany editorial Dr Jeffrey Drazen, editor of the New England Journal of Medicine, and Dr Mark Klempner write that the vaccine could help save lives in parts of Asia affected by the Boxing day tsunami. “Should health officials determine that pre-emptive vaccination is indicated, the gift of the vaccine to the tsunami survivors could help prevent an outbreak of cholera and cholera-related deaths,” they write. “If this approach is needed, we hope that the World Health Organization will be able to mobilise the resources needed to distribute the vaccine in areas where it will do the most good.”