Whatever one thinks about the ‘95% effective’ claims even the most enthusiastic commentators have acknowledged that measuring vaccine efficacy two months after dosing says little about just how long vaccine-induced immunity will last. The concern, of course, was decreased efficacy over time. ‘Waning immunity’ is a known problem for influenza vaccines, with some studies showing near zero effectiveness after just three months, meaning a vaccine taken early may ultimately provide no protection by the time ‘flu season’ arrives some months later.
If vaccine efficacy wanes over time, the crucial question becomes what level of effectiveness will the vaccine provide when a person is actually exposed to the virus? Unlike Covid vaccines, influenza vaccine performance has always been judged over a full season, not a couple months.
And so the recent reports from Israel’s ministry of health caught my eye. In early July, they reported that efficacy against infection and…