The impact of vaccine mandates is modest, but potentially crucial

IN THE 24 hours after France announced that it would require proof of vaccination or a negative covid-19 test to enter many public spaces, 1m people signed up for jabs. Other countries are following suit: Italy imposed a vaccine-or-test policy last week.

How effective will such rules be? The response in France was robust, but many of those people might have sought jabs anyway. In American polls, most unvaccinated people say they do not intend to get shots.

Because jabs for covid-19 are new, the impact of mandating them will probably differ from that of requiring children to get well-established vaccines. However, history still offers relevant data on hardline refuseniks’ susceptibility to legal fiat.

The link between mandates and uptake of standard vaccines in childhood is murky. Much of Europe enjoys broad coverage without mandates, whereas poor countries’ edicts are often honoured in the breach. Even among countries with similar GDP per person, those with mandates do not vaccinate more—perhaps because only places with low uptake resort to coercion.

Another way to assess impact is studying changes over time when new mandates come in. Uganda’s long-run upward trend in jab rates actually flattened out after the country imposed a mandate. However, it only began requiring vaccines once 80% of children were already getting them.

In rich countries mandates have helped a bit. In 2016 Australia ended an exemption for conscientious objectors. Its jab rate for polio rose by three percentage points. After imposing new mandates in 2017-18 following outbreaks of vaccine-preventable diseases, Italy saw gains in measles shots, and France in meningitis-C jabs. In six countries that have stiffened rules since 2000, the average gain was 2.2 percentage points.

The best evidence that mandates matter comes from America. Some states offer carve-outs from mandates only for medical reasons; others also recognise religious or philosophical ones. After adjusting for demographic and political characteristics that also affect jab rates, uptake in states with the fewest exceptions is 1.1 percentage points higher than in those with the most.

These effects sound small. But since jab rates cannot exceed 100%, mandates can only do so much if uptake is already high. Moreover, for diseases like measles, 95% of people need protection to reach herd immunity. A few percentage points can determine if outbreaks take off or fizzle out.■

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