A study appeared in the Lancet this week confirming that vaccine effectiveness against infection is fading fast.
The study involved 3,436,957 people over the age of 12 who are members of the healthcare organisation Kaiser Permanente Southern California. It sought to assess the effectiveness of the Pfizer vaccine against SARS-CoV-2 infections and COVID-19-related hospital admissions for up to six months, with a study period covering December 14th, 2020, to August 8th, 2021.
Comparing fully vaccinated to unvaccinated, and controlling for confounders such as prior infection, the researchers found that effectiveness against infection plummeted from 88% (95% confidence interval 86-89%) during the first month after double-vaccination to 47% (43-51%) after five months. The variation by age (depicted above) was largely within the margins of error.
Among sequenced infections, the researchers found vaccine effectiveness against Delta infection was 93% (85-97%) during the first month after double-vaccination but dropped to 53% (39-65%) after four months. Effectiveness against infection from other variants the first month after double-vaccination was 97% (95-99%), but declined to 67% (45-80%) at 4-5 months.
Vaccine effectiveness against hospital admissions for Delta infection held up at around 93% (84-96%) for the six months across all ages.
However, the researchers note that the latest data from Israel “suggests that some reduction in effectiveness against hospital admissions has been observed among older people (65 years and over) roughly six months after receiving the second dose of [Pfizer]”.
One question that’s arisen recently is to what extent vaccine effectiveness estimates are affected by whether more people who have been previously infected decide not to be vaccinated. According to this study the answer is: not very much at all. Among the unvaccinated, 2.3% had one or more previous positive PCR tests, only slightly more than the 2% of the double-vaccinated who did.
It’s also worth noting that although this study adjusts its raw estimates for no fewer than 22 potential confounding variables, the adjusted figures differ very little from the unadjusted figures in almost all cases. This suggests that unadjusted estimates from large population samples are often a fair approximation in the absence of sophisticated statistical analysis.
Given that the adjusted figures were little different to the unadjusted figures, however, it’s not immediately clear why the vaccine effectiveness estimates in this study, while low and declining, are so much higher than the latest unadjusted estimates derived from Public Health England data (namely, negative vaccine effectiveness in the over-40s, including minus-66% in those in their 40s). It doesn’t appear to be merely a matter of additional time elapsing, as most people in the U.K. weren’t double vaccinated until April, May or June, meaning only four or five months have elapsed until September, the same time period as in the study.
Could it be because the study period ended on August 8th, when the Delta surge in California was just getting going (see below)?
In the U.K. the vaccine effectiveness didn’t plunge until the second half of the Delta surge, the first part being dominated by infections in the unvaccinated (for reasons still not entirely clear). Did the new study finish too early to see the dramatic effect we’ve seen in England?
The authors say their study indicates that the decline in vaccine effectiveness is primarily a function of time rather than variant-related. However, the evidence from England would suggest otherwise, as in the same period of time, but later in the Delta surge, the decline has been far greater.
The decline in vaccine effectiveness in England was confirmed last week in a new Government-funded study (not yet peer-reviewed), which found that the reduction in transmission “declined over time since second vaccination, for Delta reaching similar levels to unvaccinated individuals by 12 weeks for [the AstraZeneca vaccine] and attenuating substantially for [Pfizer]”. In other words, within just three months AstraZeneca did nothing to prevent transmission, and Pfizer was scarcely better.
One of the main recommendations of the authors of both studies in light of their findings is for regular booster jabs – in the case of the first, where many of the authors are employees of and investors in Pfizer, this may be deemed hardly surprising. However, if effectiveness against serious disease is holding up, why give people boosters just to stop them getting and spreading what is effectively a cold, and which bestows more robust immunity as it goes? Furthermore, if the effectiveness declines after as little as three months, is it even possible to deliver enough boosters to have any impact on infection and transmission? Would it not be much better to say that the vaccines, by offering personal protection from serious disease to those who want it, have done their job? Better to move on and abandon any ideas of vaccine passports and mandates and boosters, and in general the now almost wholly pointless obsession with Covid vaccines.
