With all the news and chatter about coronavirus vaccine candidates these days, it might be somewhat surprising to learn that sales of established vaccines have been dropping lately.

Biopharma Dive reported that the world's top four vaccine makers -- pharmaceutical giants Pfizer (NYSE:PFE), Merck (NYSE:MRK), Sanofi (NASDAQ:SNY) and GlaxoSmithKline (NYSE:GSK) -- have all experienced notable volume declines in the category.

Sanofi's vaccine sales fell 7% on a year-over-year basis in its most recently reported quarter. Its European peer GlaxoSmithKline suffered sales drops in all components of its vaccines unit, with sales of one of its top products (Shingrix, aimed at preventing shingles) sliding by 16% -- its steepest decline ever.

A syringe being filled with a vaccine from a vial.

Image source: Getty Images.

The primary reason for this is, of course, the coronavirus pandemic. While the health crisis has heightened public awareness of the need for effective vaccines, the shelter-in-place measures it has engendered have kept many people out of doctors' offices. Additionally, many people might not consider getting vaccinated for those long-established illnesses as urgently necessary right now.

The immediate future doesn't look rosy for the vaccine segment, as local coronavirus outbreaks have intensified rapidly in a majority of U.S. states over the past two months, with the rates of daily new diagnoses reaching peaks many times higher than they were in April, when the country's early hot spots had their worst days. Even if renewed efforts to reduce transmission do bring those new case numbers back down before the end of this year, many people will likely continue to avoid social contact situations such as doctor visits when they can.

However, some of the affected companies sounded hopeful notes, and a few believe that a turnaround will come soon. "We expect to see vaccination rates recover in the second half of the year," said GlaxoSmithKline's CEO Emma Walmsley.

Meanwhile, Thomas Triomphe, Sanofi's head of vaccines, spoke of his company's "readiness for a record flu season," as it is seeing high preseason demand for this year's version of its influenza vaccine.