На самом деле, так пишут не везде. Вот, например, с сайта Минздрава США (про сезонный грипп, но это не суть)http://www.cdc.gov/flu/about/qa/misconceptions.htmMisconceptions about the timing of seasonal influenza vaccinationIs it too early to get a flu vaccine in September?No. CDC recommends that providers begin to offer flu vaccine as soon as it becomes available in the fall. Immunity from vaccination will last throughout the year.Is it too late to get vaccinated after Thanksgiving (or the end of November)?No. Vaccination can still be beneficial as long as influenza viruses are circulating. CDC recommends that providers begin to offer influenza vaccination as soon as vaccine becomes available in the fall, but if you have not been vaccinated by Thanksgiving (or the end of November), it can still be protective to get vaccinated in December or later. Influenza is unpredictable and seasons can vary. Seasonal influenza disease usually peaks in January or February most years, but disease can occur as late as May.