At the most basic level, this pandemic has always been about a battle between hordes of mutating viruses and billions of human hosts, with no clear victor or end as yet in sight.

This fight is similar to other battles, such as those between mutating cancer cells and oncological tools such chemotherapy and novel immunotherapies or in the case of bacterial infections, between the bacteria and antibiotics.

In each example, whether viruses, cancer cells or bacteria, left alone to multiply, continuing mutations may stumble on solutions to therapies or the host’s defences. They all illustrate the power of evolution on the fast track in which emerging, random mutations coupled with natural selection, compete against defences to dictate the outcome.

Until a few months ago, it looked as if we were winning, what with the widespread availability of effective vaccines and vaccination programs, especially in the western world.

As of July 31 in Ontario, 70.2 per cent of adults were fully vaccinated and 81.3 per cent had received one shot. Those are impressive numbers and quite an achievement – well ahead of current numbers in the United States, mostly because vaccine reluctance or refusal poses less of a challenge in Ontario and the province hasn’t fully opened up the way many U.S. states have.

However, this is no time for a victory lap in Ontario or anywhere else. Look at the rush these days to open up international travel, sporting events, restaurants and other highly social activities in the United States, U.K. and Europe and the disconnect between those pressures and what’s happening in Japan, Australia, almost all of Africa, the chaos in the “red” states and beyond, south of the border and the recent severe outbreak in China sparked by a single flight from Russia, which led to lockdowns in several major Chinese cities – all apparently related to the Delta variant.

The Delta variant is a hint of possible variants to come. This variant is much easier to catch and pass on compared to the Alpha variant, which was itself much more transmissible compared to the original virus.

The fact that even fleeting contacts are sufficient to pass on this variant is consistent with the observation that the viral load carried by asymptomatic unvaccinated people and even some fully vaccinated cases with the Delta variant, is often much higher compared to cases carrying the Alpha variant.

Of course, no vaccine is perfect. Breakthrough infections were always a possibility in fully vaccinated cases long before the Delta variant emerged. But in a recent study of the largest health care facility in Israel, breakthrough infections were observed in a small group of fully vaccinated health care workers.

Fortunately, most of those who tested positive were asymptomatic. However, in a small number of cases, infection was associated with cold-like symptoms and in some instances, the development of long COVID symptoms. That’s worrisome and perhaps why Israel intends to offer a third shot to those 60 years of age and over as a caution. That’s a wise decision and will likely lead to extending the booster to younger Israelis.

We also know that some of the major vaccine manufacturers such as Pfizer BioNTech and Moderna have taken steps to update their vaccines to include protection against the Alpha, Delta and other known variants, as possible booster shots should they be required.

That’s the kind of forward thinking we need because, as with known variants, new ones may spring up without much notice and as was the case for the Alpha and Delta variants, each of which became the dominant variant within a few weeks, especially when countries open up their borders. The recent outbreak in China is a lesson to be heeded.

If anyone needs reminding, surely the surging numbers of cases in so many countries around the world makes the point. This is a worldwide problem and cannot be solved without looking after our brothers and sisters everywhere, not just protecting those within our borders.

Sharing vaccines with hot spots elsewhere in the world helps us as well as them corral what has become a highly transmissible virus, rivaling chickenpox which for those of us who remember, was very easy to pass on.

Our concern should be variants we don’t yet know about. Remember, evolution is opportunistic and in the case of SARS-CoV-2, quick to exploit weaknesses in public health measures, including our behaviour, vaccines and our immune systems.

Most worrisome of all would be breakthrough infections that go beyond common cold symptoms to involve the lower respiratory tract and beyond. That would be a nightmare revisited in long-term care facilities and beyond.

The evidence is worrisome and as we’ve learned in this pandemic, evidence counts.

Dr. William Brown is a professor of neurology at McMaster University and co-founder of the Infohealth series at the Niagara-on-the-Lake Public Library.