Sunday, April 11, 2021

Panic mongering

For today's exercise in looking behind the headlines, consider this vaccine story.


Headline of the linked article "Israeli data shows South African variant able to ‘break through’ Pfizer vaccine"

Subhead: "Strain is more effective than original COVID and the British variant at bypassing the shot, Israeli scientists find, in first-of-its-kind, real-world study"

Paragraph 3-4: "A team from Tel Aviv University and the Clalit healthcare organization sequenced the swabs of 150 Israelis who tested positive for COVID-19 despite having been vaccinated. ...the prevalence of the South African strain among vaccinated individuals who were infected despite their inoculation was eight times higher than its prevalence in the unvaccinated infected population."

Paragraph 5: "we would have expected just one case of the South African variant, but we saw eight". It does not say if they presented with symptoms before being tested--that matters.

Pfizer: "vaccine effectiveness was at least 97% in preventing symptomatic disease" based on Israeli data. "94% against asymptomatic SARS-CoV-2"

Note that the numbers involved in the new study are extremely small and statistical fluctuations can be significant. In addition, there's reporting bias (bad news is news). But just for laughs, take the numbers at face value. And lets assume that this was random testing, and not people presenting with symptoms.

For the original strain, the Pfizer is 94% effective at preventing infections. If you continue to get 8x as many cases with the new strain as you expect, that would mean the vaccine is about 52% effective (plus or minus a large number which we'll ignore for now).

The Johnson and Johnson vaccine is reported to be 66% effective at preventing infection (and "high efficacy at preventing hospitalization and death in people who did get sick". So the Pfizer is slightly worse with the new strain than the J+J is with the old strain. Maybe. If this group of 150 had symptoms the relevant Pfizer number is 97%, and its effectiveness against the new is 76%--better than the J+J.

So walk back up the headlines. The subhead is technically accurate, but doesn't give any idea of the scale ("more effective ... at bypassing shot"). The headline is misleading ("able to break through"). The clickbait headline ("can't stop ... strain") is a lie.

1 comment:

Assistant Village Idiot said...

And your symptoms will be much less even if you get the variant form, which is also not mentioned. So the vaccines might need an upgrade, but it's not an emergency. That's fine.