This is the question that many are asking, but unfortunately, there is no easy answer.
First of all, we have to take a look at why the cold and flu viruses seem to dissipate in the summer months. There are four possible reasons why respiratory viruses are more common in the winter and tend to become less of a problem in the summer.
1. Less Humidity – In the winter the air is colder and drier. This has been proven to favor the viability of the flu virus. However, this may not be a characteristic of the SARS-CoV-2 virus. It has been pointed out that Singapore had larger numbers of infected people, even though it is very close to the equator and more humid than in the North. The droplets from a sneeze or cough do not stay suspended in humid air as long as with dry air, and the warmer temperatures lead to increased virus degradation.
2. More Indoor Activity – In the colder months, people tend to remain indoors, where they are more likely to pass on viral disease. People are more confined and children are together in classrooms during this time. Young people are often asymptomatic carriers of Covid-19. This being the case, it could be that school closures will be of some assistance in controlling the spread of the virus this summer.
3. Weaker Immunity – Vitamin D is involved in many immune functions of the body. During the winter in the Northern Hemisphere, the sun is not high enough in the sky and shining long enough to provide adequate UV-B rays for vitamin D production in the skin, which is usually covered up anyway due to colder temperatures. There is evidence that higher levels of vitamin D help to reduce the incidence of respiratory infection. Whether the novel coronavirus will be inhibited by higher vitamin D levels in the blood remains to be seen.
4. Less Herd Immunity – When a new stain of virus emerges in the winter, the population in general has less immunity at the beginning of the season. As the season progresses, more people develop immunity, which helps to lower the rate at which infections are passed on to others.When the current flu virus is related to previous strains, the season of infection tends to be shorter due to this herd immunity. However, when a novel virus, different from previous ones, appears, the season is prolonged until more people are exposed and become immune.
Unfortunately, seasonality does not appear to constrain novel viruses in the same way that it does for the older more familiar viruses. Past coronavirus outbreaks, SARS and MERS, haven’t exhibited clear evidence of being seasonal. Contrast that with the H1N1 Swine Flu of 2008, which did adopt a seasonal pattern.
A study published in mid-March by researchers from Spain and Finland, found that 95% of infections globally have so far occurred at temperatures between about 28° and 50° F, and in dry climates. This may sound promising, but Malaysia and Singapore were hit hard by the virus and their average temperature is 80° F year round. Clearly, more research and experience with this novel virus is needed.
Marc Lipsitch, PhD, an epidemiologist at Harvard University, summed it up in this statement, “Based on the analogy of pandemic flu, we expect that SARS-CoV-2, as a virus new to humans, will face less immunity and thus transmit more readily even outside of the winter season. Changing seasons and school vacation may help, but are unlikely to stop transmission.”