How long do viruses live?
“Forever,” says Dr. Catherine Troisi, a UTHealth epidemiologist who specializes in infectious diseases. Dr. Troisi points to influenza, which has been around for centuries, to demonstrate viral longevity, and highlights smallpox as the only virus that has been completely eradicated. We're close with measles and are working on polio, but they're still with us. Viruses have a very long shelf life.
Most viruses come from animals, as is suspected of the novel coronavirus that causes Covid 19, and those viruses can spread to humans, sometimes easily from person to person. It is in those early stages of high transmissibility that the virus can be most deadly. They'll change over time, she says, sometimes over decades, and become less deadly as humans develop antibodies and adapt genetically, becoming less vulnerable to infection. Dr. Troisi says the Covid 19 virus won’t go away any time soon, and could become endemic, meaning always present but less potent. Think of the common cold.
Medical science has been planning for a pandemic for a good while, however the expectation was that when it emerged the contagion would be caused by one of the four strains of influenza virus. Instead, we got a novel coronavirus. Coronaviruses have been around for a very long time, Dr. Troisi says.There are four kinds of coronavirus that can cause the common cold, as well as other viruses thrown in for good measure, and although a really bad cold may cause you to feel like you’re dying, the illness tends to not be fatal. The common cold demonstrates, she explains, how viruses weaken over time with broad exposure but don’t ever disappear entirely. It just keeps coming back each year with the autumn winds. Scientists have been working since the 1950’s to develop a cold vaccine, but because it isn’t caused by a single, isolated virus, but rather rhinoviruses and another 200 types, the goal remains elusive. Unlike the lumbering cold, the four common strains of influenza virus can suddenly change, requiring updates to annual flu shots, but the flu endures as the cold does. The singularity of the SARS CoV 2 virus renders it susceptible to vaccine development, until by mutation it's not, but it won't go away. That requires a different game plan. .
It is reasonable to think we'll be getting Covid 19 annual booster vaccines in the future to adapt to mutations. It is believed now, she says, that natural antibodies to the SARS Co V 2 virus last about eight months, though that’s a preliminary assumption that we will only know with time, and the current strain could be utterly disrupted by variations. The number of variants is determined by the amount of human population that becomes infected. Each time a virus copies itself there is a possibility of mutation occurring in the replication process, some mutations proving more deadly to the virus and some more deadly to the infected human. It is the very high rate of global infections today that is driving the number of variations, those from the UK, South Africa and Brazil getting the most attention now. Though there has been a lot of talk about the high contagion level and possible higher morbidity being demonstrated by the B-1.351 variant, first identified in South Africa, Dr. Troisi says it is that Brazil variant that is keeping her up at night. In the city of Manau in Brazil, in April of last year an estimated three out of four residents were infected with the first wave of Covid 19, and those individuals were thought to be immune, yet the Brazilian P-1 variant sweeping through in October appears to have caused even higher levels of illness among those who had already been infected. The UK variant seems to be more contagious though no more deadly than early waves; if it spreads to more people it will cause more people to die. The B-117 UK variant is projected to be the dominant strain in the US by next month, but we are hampered in this country by limited genetic sequencing of the viruses in circulation, and don't know what the Brazil variant will do, or if there will be others more deadly in our future.
Where do we go from here? Dr. Troisi says we need better surveillance in areas where humans are clearing forest and encroaching into the wilderness where animals, especially bats but others as well, dwell. Bats, for some reason, carry coronaviruses but don't get sick and die from them. The next mass contagion could break out on any continent, and could strike at any time. If we are to catch the next pandemic before it takes off, Dr. Troisi says, there is nothing to be gained from putting our collective head in the sand and thinking it won’t all happen again. Odds are – it will, while Covid 19 is still lingering.
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