Over the last few months, many countries around the world have introduced vaccine passports and/or vaccine mandates. While some of these schemes are more accurately described as ‘immunity passports’ – since they recognise natural immunity from previous infection – many of them of do not.
In the U.S., there are already examples of healthcare workers with natural immunity being fired for refusing to comply with vaccine mandates. And this is despite the fact that natural immunity provides better immunity against infection than the vaccines.
Similarly, the UK’s vaccine mandate for care home workers does not include an exemption for those with natural immunity. Indeed, bioethicists at the University of Oxford have argued that it should include an exemption, on the grounds that natural immunity is at least as good as what the vaccines provide.
One potential counter-argument is that even natural immunity wanes, so those who’ve already been infected still stand to benefit from vaccination. However, this ignores the risks side of the equation. And while such risks might be low on average, they appear to be greater for young people – who face almost no risk from Covid to begin with.
What kind of risks are we talking about? First, there’s the ‘tail risk’ that the vaccines have serious long-term effects, which haven’t shown up in the data yet. Although this seems unlikely, it shouldn’t be dismissed entirely. Second, there are the rare but quantifiable side effects that we do know about.
The need to take account of both benefits and risks for those who’ve already been infected was summed up well by the vaccine scientist Christine Benn. (I found this quote in a BMJ article by Jennifer Block, which is definitely worth a read.)
If natural immunity is strongly protective, as the evidence to date suggests it is, then vaccinating people who have had covid-19 would seem to offer nothing or very little to benefit, logically leaving only harms—both the harms we already know about as well as those still unknown.
Of particular importance is the fact that ‘adverse events’ (i.e., side effects) appear to be more common in those who’ve already been infected. This has been found in at least half a dozen studies, based on data from several different countries. See here, here, here, here, here, here, here, here and here.
(I also found two studies reporting that adverse events were not more common in those who’ve already been infected. However, one of these studies had only two people with prior infection in the sample, so it doesn’t really tell us anything.)
Several of the studies that did report a difference simply compared the frequency of adverse events between those with and without prior infection. This leaves open the possibility that any difference is due to those with prior infection being younger.
However, some studies actually controlled for age and sex, and still found elevated rates of adverse events among those with prior infection.
Now, the vast majority of adverse events reported in these studies were mild or moderate – things like fatigue and flu-like illness. Yet one study found that severe side effects were more common among those with prior infection. Of course, this is just one study, so it shouldn’t be given too much credence.
A higher risk of fatigue or flu-like illness might not actually change the cost-benefit calculus for someone with prior infection who’s deciding whether to get vaccinated.
However, the evidence suggests that those who’ve already been infected not only face lower benefits from vaccination; they also face higher – or at least slightly higher – costs. (The cost-benefit ratio may be particularly unfavourable for young people who’ve already been infected.)
Vaccine passports and vaccine mandates are objectionable for a whole number of reasons. And when it comes to those who’ve already been infected – which will soon be most of us – there’s no case for them at all.
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