A surprising drop in the number of coronavirus infections in a number of countries around the world has puzzled health experts, leading some to conclude that some populations may be starting to achieve herd immunity.
Indicators for the pandemic have been on the decline for the past six weeks around the world, despite fears that the winter resurgence – dubbed the ‘second wave’ in many countries – would continue on until mid-spring.
In Canada, for instance, the number of newly diagnosed cases of COVID plummeted from more than 57,000 per week in the beginning of January to roughly 20,000 per week by the end of the month.
The infection rate has also fallen dramatically in the US during the same period, falling from about 1.7 million new cases per week in the beginning of January to under 600,000 per week in mid-February.
The number of coronavirus-related deaths in the US has also started to decline, falling roughly 21% from early to mid-February, The Atlantic reported. Hospitalizations during the same period are down nearly 18%.
The declines come despite projections by the Centers for Disease Control which anticipated that the number of new cases would not only not decline yet, but would likely continue to grow through the end of the month.
Health experts have found no clear reason for the sudden declines, though some say it suggests at least some populations are starting to achieve herd immunity – whereby a large enough portion of a given population has immunity either from natural infection or vaccination to prevent mass outbreaks of the virus.
“It could be that there is already some degree of herd immunity that has been developed,” said Prof. Eran Segal of the Weizmann Institute of Science, according to a report by Channel 12 Sunday. “But there is no clear answer.”
“Many countries are now under lockdown or are ending their lockdowns, so that their influence is notable. Following an increase in infections, there has been a change in behavior, now that the public understands the consequences that can come from becoming infected.”
“There could also be some seasonal effects on the virus’ spread,” Segal added.
“Another possible reason for the declines is that many places around the world which had very high infection rates may now have already developed partial herd immunity.”
In Israel, however, the recent decline in the pandemic is likely attributable primarily to the mass vaccination campaign, Segal said, noting that the declines began among the over-60 age cohort – which were the first to receive the vaccine.