So, Christmas, it seems, will not be cancelled after all. The government has decided instead to tackle fears of a January spike in cases with tougher messaging, telling people that just because they will have the legal right to mix for five days next week doesn’t necessarily mean they ought to avail themselves of that freedom. In other words, we’re not changing the rules, but we’d really rather you didn’t take advantage of them.
But could the vaccinations which have already been performed save us from a post-Christmas spike? The Pfizer vaccine – the only one being given to the general public so far – is designed to be given in two doses, 21 days apart. The first people to be given the vaccine had their first jab last Tuesday, 8 December. Therefore, they won’t be receiving their second jab until 29 December, too late for Christmas.
Nevertheless, does the first jab on its own confer any immunity from Covid-19? Data from the US Food and Drug Administration (FDA) suggests yes – although not until about 14 days after the first jab. The FDA has plotted infections among participants in the phase 3 trial of the Pfizer vaccine and found that until about 14 days after the first jab, infections among the group given the vaccine followed the same path as those given the placebo. At that point, the two curves began to diverge sharply, with few infections among the control group after that stage.
That implies that the first people to take part in the community roll-out of the Pfizer vaccine in Britain ought to be pretty well protected from around 22 December – just in time for the five-day Christmas window. However, relatively few people will have received their first dose of the vaccine on the first or second days. The government announced this morning that 137,000 people have received their first dose in the first seven days, but only those who received it on Friday 11th or beforehand can, to judge by the FDA data, expect to have any kind of immunity on Christmas Day. Even then, we don’t know how many of those people will remain infectious – even if they themselves have immunity from serious illness.
Admirably, the government has opted to leave the matter of Christmas to our own judgment, rather than try to manage the situation with yet more rules and punishments. But in informing people of the risks, it would do well to remind those who have already received their first vaccine dose – and who may have some degree of immunity as a result – that they will remain as vulnerable to the disease as everyone else up until about 14 days after the jab.
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