Published Date: 2003-01-03 23:50:00
Subject: PRO> Smallpox vaccination strategies
Archive Number: 20030103.0018
SMALLPOX VACCINATION STRATEGIES
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: 2 Jan 2003
From: ProMED-mail <firstname.lastname@example.org>
Source: Eurosurveillance Weekly Volume 7 / Issue 1 2 Jan 2003 [edited]
>...the public may not yet know enough about smallpox to be able to make an
Further information in support of a selective smallpox vaccination policy
A number of countries are beginning to implement plans to offer smallpox
vaccination to sub-groups of healthcare workers in advance of a deliberate
release (1, 2). At the same time there have been calls for mass vaccination
of the public, or vaccination of the public on a voluntary basis. In the
United States (US), while concentrating on selective vaccination, the
government has decided to make the vaccine 'available to all' from 2004 (3).
The European Commission Taskforce on Bioterrorism (BICHAT) has commented
that a number of complex issues and present uncertainties would make a
one-to-one translation of the US plan to the European situation an
unjustified oversimplification (4).
A series of articles was published electronically ahead of print publication
in the New England Journal of Medicine on 19 Dec 2002 and aims to provide
informed guidance on the current public health question 'whom should we be
vaccinating?' By highlighting the adverse consequences of a mass vaccination
policy, the articles support current plans for selective smallpox
vaccination, and provide physicians with information to help them educate
their patients when the inevitable requests for vaccination are received.
Mack counsels against widespread pre-emptive vaccination, either of
healthcare workers or the public, because historical records indicate that a
smallpox outbreak could be successfully and rapidly controlled (5). The
disease is likely to be easily distinguishable, the virus is not highly
contagious, and the interval between successive cases (about 14 days) makes
transmission of infection open to intervention.
A new mathematical model from Bozzette et al. favours prior vaccination of
healthcare workers (6). The balance in favour of vaccination is biased
towards the likelihood of an attack, which is difficult to assess. Their
results show that pre-emptive vaccination of 10 million healthcare workers
produces net benefits in terms of lives saved when the probability of a
'large' attack (350 initial cases of smallpox) exceeds 0.22. Pre-emptive
mass vaccination of the general public saves lives on a net basis only when
a 'massive' attack (5000 people initially infected) is expected (probability
greater than 0.22).
Sepkowitz considers adverse effects due to secondary spread of vaccinia, a
factor that has not yet been taken into account in mathematical models (7).
Complications from transmission of vaccinia have been described in 112 cases
in the twentieth century, including 12 deaths. Most of these occurred in
hospitals. If healthcare workers are to be vaccinated, it is essential that
adequate precautions be taken to prevent spread of vaccinia to patients,
especially now that many of them are immunosuppressed due to illness or
Voluntary vaccination of the public has its advocates both among health
professionals and in the media. However, a paper from Blendon et al. shows
that the public may not yet know enough about smallpox to be able to make an
informed decision (8). In a questionnaire survey of 1006 US adults with a
response rate of 65 percent, most people had misconceptions about the
disease. Despite 25 percent saying it was likely they would die from the
vaccine (6 percent thought this was very likely), over 60 percent said they
would choose to receive vaccination as a precaution against a terrorist
An issue that is not mentioned in these articles is the opportunity cost of
smallpox vaccination. It may cause harm not only directly, but through the
potentially very large resources consumed that might be better used to
prevent or treat other diseases, and also by having a negative effect on
public attitudes to other components of national immunisation programmes. It
is essential to ensure that current smallpox vaccination policies are
developed and implemented in the context of overall public health priorities
and strategies, and that they are underpinned by sound science and risk
1. Harling R. Interim guidelines for smallpox response and management
published in the United Kingdom.
Eurosurveillance Weekly 2002; 6: 021205
2. CDC. Protecting Americans: Smallpox Vaccination Program.
3. Bush orders military smallpox shots. NY Times, 13 Dec 2002, cited in
ProMED-mail 13 Dec 2002
4. Hendriks J, Tegnell A, Bossi P, Baka A, Van Loock F, Wallyn S et al.
United States smallpox response plans: a commentary from the Bioterrorism
Taskforce (BICHAT) perspective. Eurosurveillance Weekly 2002; 6: 021024
5. Mack. A Different View of Smallpox and Vaccination. N Engl J Med 2003:
348; 5: MACK 1-4. [Electronic publication ahead of print].
6. Bozette SA, Boer R, Bhatnagar V, Brower JL, Keeler EB, Morton SC et al.
A Model for a Smallpox-Vaccination Policy. N Engl J Med 2003: 348; 5:
BOZETTE 1-10. [Electronic publication ahead of print].
7. Sepkowitz. How Contagious Is Vaccinia? N Engl J Med 2003: 348; 5:
SEPKOWITZ 1-8. [Electronic publication ahead of print].
8. Blendon RJ, DesRoches CM, Benson JM, Herrmann MJ, Taylor-Clark K, Weldon
The Public and the Smallpox Threat. N Engl J Med 2003: 348; 5: BLENDON 1-7.
[Electronic publication ahead of print].
Public Health Laboratory Service
Communicable Disease Surveillance Centre
[This is an excellent summary of the recent articles in the New England
Journal of Medicine addressing the smallpox vaccination issues. Interested
subscribers are strongly urged to read the articles for themselves as well
as the Eurosurveillance Weekly article of 24 Oct 2002 discussing the US
It does appear that there are more questions than answers, along with
different answers to the same questions as to what the most appropriate
international strategy should be for smallpox vaccination. One continues to
hope that the decisions that are made are based on utilization of good "data
for decision-making". This moderator stands by her comment on 25 Dec 2002
(Smallpox vaccination strategy - Israel (04) 20021225.6123 ): "In the
absence of known circulation of the smallpox virus (variola virus), efforts
to reduce adverse events associated with the currently available smallpox
vaccines (vaccinia virus) seem prudent, while efforts focused on research
and development of a newer and safer vaccine should maintain a high
priority." - Mod.MPP]