Will we have a 4th wave of COVID? The waves are caused by relaxing our guard when things look good, combined with not acting quickly enough when cases start ticking up again. The waves have been spaced about 4-5 months apart, so I’d expect the next one around the end of March (about 5 weeks from now).
The next wave will be smaller, because by then about a third of the population will be vaccinated. Maybe that, combined with the number who have already recovered, will be enough to reach herd immunity.
Some people have mistakenly supposed that the current drop-off in cases is due to vaccination. That’s not a sufficient explanation, because we don’t have enough people vaccinated yet, and the vaccines have been restricted to the elderly and health workers, not the people who do most of the spreading. The real explanation, in my humble but educated opinion, is the same thing that ended the first and second waves, simply an increase in preventative behaviors like masking, social distancing and lockdowns.
Right now we’re engaging in the exact same behaviors that created the second and third waves, so a 4th wave is inevitable unless we’ve truly reached herd immunity. If a 4th wave does not develop by the end of April, that would be the time to celebrate the end of COVID.