Long Covid Is Even Less Common Than Previously Thought

In a post on long Covid back in July, I said that “estimates of the chance of reporting symptoms after 12 weeks range from less than 1% to almost 12%”. That 12% figure came from the ONS, who found that individuals who tested positive were 12 percentage points more likely than controls to report at least one symptom 12 weeks after infection.

In my post, I argued that 12% is probably an overestimate on the grounds that some people who tested positive might have been inclined to exaggerated their symptoms – to report things they normally wouldn’t have done (thanks to all the media attention on long Covid).

And I noted that a study published in Nature Medicine had observed a much smaller percentage of people still reporting symptoms 12 weeks after infection, namely 2.3%.

A new analysis by the ONS has obtained a figure almost identical to that observed in the Nature Medicine study, namely 2.5% (the difference between the blue and green lines in the chart below). This is clearly much lower than its previous estimate.

Interestingly, the reason for the discrepancy with the earlier figure isn’t the one I suggested (i.e., that some people who tested positive were inclined to exaggerate their symptoms). Rather, it’s a statistical issue.

In both their original and updated analyses, the ONS defined symptom discontinuation as two consecutive visits without reporting any symptoms. (Participants in the ONS’s survey were visited at regular intervals for the purpose of data collection.)

This means that someone would be classified as ‘having symptoms’ if they’d gone one, but not two, visits without reporting any symptoms. However, in their original analysis, participants were only followed for a median of 80 days (less than 11 weeks).

As a result, some participants who would have been classified as ‘not having symptoms’ if they’d been followed a little bit longer were still classified as ‘having symptoms’ at the end of their observation period. (In the jargon, their follow-up time was ‘right-censored’.) This is shown in the diagram below, taken from the ONS:

In the ONS’s updated analysis, which followed participants for a median of 204 days, individuals in the situation of Participant D above were correctly classified as ‘not having symptoms’ before the end of their observation period.

Using this revised method, the ONS found that less than 1% of children aged 2-11 continue to report symptoms 12 weeks after infection, with the figure rising to just 1.2% for those aged 12-16. Hence long Covid is particularly rare in children, further undermining the case for vaccinating that age-group.

While the ONS deserves credit for being completely transparent about the limitations of their original analysis, their updated analysis is still open to the criticism I mentioned above. This means that 2.5% should probably be considered an upper bound on the chances of getting long Covid, the true figure being somewhat lower.

ZOE Data Shows Vaccines Cut Hospitalisation Risk by 64% once Infected, but Data on Frail Elderly is Less Positive

Professor Tim Spector, who leads the ZOE Covid Symptom Study, has done a new video update on vaccines, which is worth a watch. The team has also published a new study (not yet peer-reviewed) about the vaccines and their effect on symptomatic Covid.

The data is broadly encouraging in terms of efficacy. (They don’t address safety, though a previous study did. They also exclude the period immediately after each vaccine dose, so the study tells us nothing about any post-jab spike in infections, which is disappointing.)

One interesting finding is that sneezing becomes more common as a symptom of Covid infection after vaccination than beforehand, which the authors suggest could be a result of our immune system reaction changing. They note this could make the disease more infectious owing to the additional aerosols produced.

A concerning finding was that the elderly (over-60s) were up to three (2.78) times more likely to be infected after being vaccinated (with one dose of any vaccine) if they were frail than if they weren’t. This is unsurprising perhaps, but still indicative of considerably lower protection for those already at higher risk from the disease. Furthermore, a quarter of the vaccinated frail elderly in the study who contracted the virus ended up in hospital, which is not a small proportion (though no figure was given for the hospitalisation rate of unvaccinated frail elderly people against which to compare it).

Vaccine efficacy was also reduced in the obese, another high risk group, and those with an unhealthy diet – see charts below. The baselines are people who are also vaccinated and otherwise similar, but without the particular characteristic mentioned, e.g. the point in the top right shows the additional risk of infection that the vaccinated frail elderly have versus the vaccinated non-frail elderly.

Why Are People Unwell with Symptomatic COVID-19 Being Vaccinated?

Yesterday I wrote about the latest study from Public Health England that claims to show the vaccines are up to 90% effective in preventing symptomatic Covid infection in the over-65s, highlighting some shortcomings.

There was one aspect of the data that I didn’t comment on that is worth flagging up. The authors presented graphs showing how many people were being tested and testing positive according to how many days before or after their jab their symptoms began (all the tests in this study were on people with symptoms, the symptoms likely having prompted them to get a Covid test).

There are a few notable points about these graphs. The steep drop-off in tests ahead of the jab may be due to people deferring their vaccination when they get symptoms (Government guidance is that you should not have the jab if you are unwell), or it may be people with symptoms not getting tested because they don’t want to have to cancel their jab.

The big spike in tests in the day or two after the AstraZeneca jab (ChAdOx1-S) is probably people being tested after getting Covid-like side-effects from the vaccination.

Note the high positivity rate (yellow bars) in the days after each jab. This confirms the post-vaccination infection spike (though some of it may be Covid caught prior to the injection that subsequently becomes symptomatic).

However, the main point I want to draw attention to here is how many people with symptomatic Covid are getting vaccinated. The bars in the seven days prior to vaccination represent thousands of people with Covid-like symptoms who go on to get vaccinated, many while still symptomatic. The orange bars represent hundreds of people with PCR-confirmed symptomatic COVID-19, many of them with symptoms beginning in the two days immediately prior to the jab, who go on to get vaccinated anyway. This is despite Government guidance that people who are unwell, particularly with COVID-19, should be deferring their vaccinations. In addition to this, some of those thousands of people whose Covid symptoms begin on the day of the jab or in the days immediately following might have been pre-symptomatically infectious.

It has been suggested that the post-vaccination infection spike may be driven by the vaccination programmes spreading the virus. (Another plausible mechanism is that the vaccines cause temporary immune suppression; these mechanisms are not mutually exclusive and both could be operating.)

Here, then, we have direct evidence that hundreds of people with symptomatic, test-positive Covid (plus potentially thousands in the infectious pre-symptomatic phase) were turning up and being vaccinated anyway. This reinforces the idea that the vaccination programmes could be spreading the virus.

It also prompts the question: why were vaccinators not following Government guidance and refusing to vaccinate those who are unwell, particularly those with symptomatic COVID-19? Could they not foresee that that would spread the virus to those being vaccinated and those doing the vaccinating?