As Shakespeare’s Richard III has it: ‘Now is the winter of our discontent, Made glorious summer…’ But is the summer experience of COVID-19 in the hard-hit northern hemisphere looking any less inglorious than the preceding, grim days of late winter and autumn? We’re used to the idea that colds and flu are more of a problem in winter, and many would like to believe that should also true for SARS-CoV-2 infection. But COVID-19 is a new disease and we’ve only lived with it for a very short time. While New York City and London were hard hit in the colder months, hot places like India, Texas, Florida and Indonesia are currently experiencing a surge in cases. Is there really a summer lull?
Why is the summer versus winter equation for COVID-19 hard to sort out? The besetting problem is what all research scientists understand, confounding variables. Though disease prevalence and mortality rates have fallen in the ‘Big Apple’, how much of that is due to social distancing? Is the incidence of severe disease and death decreasing because treatments are improving? The antiviral drug, Remdesivir, which does seem to have some inhibitory effect on SARS-CoV-2 replication, is progressively more available in the US. Has the realisation that COVID-19 is as much a vascular as a respiratory disease led to the broader use of anticoagulant therapy (medicines that help prevent blood clots) and improved outcomes for those who are severely ill? As time goes by, of course, we will learn the answer to those questions, but it is still early days.
While our thinking is conditioned by what normally happens with influenza, one of the many features that makes COVID-19 different from the flu is the degree of involvement of children. Influenza can be lethal for the very young, and it’s well established from excellent studies done in both Hong Kong and England, that kids are a major ‘introducer’ of flu viruses into households. With the 2009 H1N1 influenza pandemic in Britain, for example, there was a dramatic drop in incidence that coincided pretty much with the long, summer school vacation. For COVID-19, on the other hand, we see little evidence that children are particularly involved, either from the aspect of spread or when it comes to the need for hospitalisation. Some children have died but, fortunately, there are few such cases.
Why should SARS-CoV-2, or any respiratory virus, cause more infections in winter? When we set aside issues that relate to human behaviour, like social distancing and hand washing, the first line of defence against the many different viruses that cause colds and flu is the 7.0 mm (7,000 nanometre) thick layer of slimy to sticky mucus (see Slime, rhyme, snot) that bathes the surface epithelium of the upper airways. All these tiny viruses, which range in size from 30-250 nanometres, are inert particles that have no mechanism for moving themselves about. Some, though, have a protein on their surface that…