Michael Ryan a spokesman from the WHO said on the BBC that it would take
at least a year to develop a vaccine against COVID19 and that it was necessary,
before its release, that the vaccine be shown to be “absolutely
safe”. This statement should not go unchallenged.
In a general sense, nothing is ever absolutely safe. It is
not safe to cross the road, to ride your bicycle, to drive your car, even to
walk up and down stairs. Everything carries at least some degree of
risk.
Turning to medical matters, it is well known that no medicine is
entirely free of risk either. Anyone who has received a prescription
medicine in a package and read the document that comes with it will see listed
a whole series of risks of different frequencies which might – but do not –
discourage people from taking that medicine if it has been prescribed for
them. In all cases, what is required is a balance between what is to
be gained from taking the medicine and the possibility of a harmful side
effect. This is always a matter of judgement, usually by the
prescribing doctor, and the idea of absolute safety is a myth and
misconception.
When it comes to vaccination, there are similar problems. One
of the great triumphs of 20th-century medicine was the eradication of
smallpox. This was done by an extensive vaccination program which
was compulsory in many countries. In the UK compulsory vaccination was
abolished in1948 by which time smallpox in the UK was virtually eradicated. A
huge eradication programme was carried out under WHO auspices in the 1960s and
70s which eradicated smallpox worldwide. Smallpox vaccination was never
entirely harmless and there were deaths during the vaccination
campaign. Each was a tragedy but on balance, the number of
cases of smallpox and the number of deaths prevented was hugely larger and at
the time the world population at large was prepared to accept such an
eradication program.
In vaccination, therefore, one has to balance the potential gain against
the possible pain. When one is immunising healthy children against a
disease they are relatively unlikely to encounter, a very high level of safety
is required. However, when one is trying to deal with a rapidly
spreading worldwide pandemic, as in the case of COVID19, the situation is
different.
In the first instance, it is necessary to demonstrate that any vaccine
is effective in producing immunity and does not contribute to the infection
through antibody-mediated enhancement. This latter complication is
known to occur naturally in the case of Dengue where second infections can
produce the hugely more severe syndrome of Dengue Hemorrhagic
fever. A similar antibody-induced enhanced infection is known with
other coronaviruses ([i])
and this needs to be tested for before a potential vaccine for Covid19 can be
used. This can be done both in animals and in-vitro by testing the
antibodies it gives rise to on cell lines. If a vaccine candidate
can be demonstrated to be free of the risk of antibody-induced enhancement and
can be shown to give rise to antibodies that neutralize the virus in-vitro,
then the balance of risk and potential gain needs to be worked out largely by
the modellers of the infection. They need to estimate the number of “Quality
Adjusted Life Years” (QALYS) that would be saved by vaccination and the QALYS
that might be lost from vaccine side effects. QALYS are used rather than lives
lost to give increased weight to effects on the young rather than the old,
Both estimates will require some in-vivo human trials but these should
no longer or larger than is necessary to make these estimates. They are also
necessary to protect the public from “snake oil salesmen”. If the gain in QALYS
is estimated to be substantially larger than the QALYS lost then it would be
wrong to reject vaccination because there is no “absolute
safety”. It is the relative advantage that is important. This is the
utilitarian- rather than the libertarian - view which is accepted for all the
other restrictions imposed on us to control the pandemic.
One problem to public acceptance of this conclusion results from the
fact that if a child (or adult) is harmed by a vaccine, his/her picture and
story can be put on to TV news and into newspapers whereas those who are
protected from developing a lethal or highly unpleasant disease are statistics
who cannot be individually identified and do not have the same public appeal.
More numerate journalism could make a real difference.
Using these criteria it
should be possible to get a vaccine into widespread use in just a few months.
(Published as rapid response: BMJ 2020;368:m1071
[i] For example: Jaume
M, Yip MS, Cheung CY, et al. Anti-severe acute respiratory syndrome coronavirus
spike antibodies trigger infection of human immune cells via a pH- and cysteine
protease-independent FcγR pathway. J Virol.
2011;85(20):10582–10597. doi:10.1128/JVI.00671-11
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