Since the outbreak of coronavirus at the end of 2019, a total of 40.3 million people became infected, 27.6 million have recovered and 1.12 million have unfortunately died due to complications. This year scientists have been working around the clock in order to find a cure and put an end to all the suffering. However, exactly when and how the coronavirus will end depends on many complicated factors such as vaccines, herd immunity and human behaviours.Currently, many countries are ending lockdowns and opening borders in an effort to return to some kind of normality, whereas others such as the UK, USA and France are needing to take on harsher restrictions to control the spread of the harmful disease. Yonatan Grad, an epidemiologist at the Harvard T. H. Chan School of Public Health in Boston, Massachusetts believes that we may actually be in it for the ‘long haul’.VaccinesAs of right now, there are 26 coronavirus vaccines in various stages of testing including 12 in stage two and six in stage three. However, the effectiveness of a vaccine in curing SARS-CoV-2 depends on how long the vaccine lasts. Harvard epidemiologist Marc Lipsitch and colleagues wrote in a paper published in May:The total incidence of SARS-CoV-2 through 2025 will depend crucially on this duration of immunity. Many vaccines such as those for polio, measles and mumps last upwards of ten years. However, vaccines for the flu only last for a small amount of time in the grand scheme of things and need to be re-taken every year. If the coronavirus vaccine ends up only lasting six months at a time (like the flu vaccine) then there is most likely to be spikes of COVI-19 up until at least 2025. The speed of production and distribution of a vaccine are also drivers in the stopping of coronavirus as well as any late discovered efficacy or safety issues. The affordability of the vaccines must also be taken into consideration as many developed countries may be able to afford the vaccines over developing countries.Getty ImagesHerd ImmunityThe WHO states that herd immunity to COVID-19 can occur when the vast majority of the population is vaccinated against the virus and as a result, the rate of transmission is slowed down a significant amount. This means that not every person needs to be vaccinated in order to be protected. The percentage of the population that needs to be immunised against a virus in order to achieve herd immunity varies. For example, for measles, roughly 95% of the population to be vaccinated. For coronavirus Tom Britton, a mathematician at Stockholm University has calculated that herd immunity can be achieved if just 43% of people are vaccinated. However, estimation from other scientists concludes that this number may even go as high as 70%. A study executed by Dr Gabriela Gomes from the University of Strathclyde in Britain also took into account variations between societies and found that Belgium, England, Portugal and Spain all the capacity to reach herd immunity at just 10-20%. Dr Gomes stated that the pandemic may last just a few more months:At least in countries we applied it to, we could never get any signal that herd immunity thresholds are higher. I think it’s good to have this horizon that it may be just a few more months of the pandemic.Gome’s predictions have been criticised by other scientists stating that until there are vaccines in place any guesses in thresholds for herd immunity are just that, guesses.Getty ImagesHuman behaviourRosalind Eggo, an infectious-disease modeller at the London School of Hygiene and Tropical Medicine (LSHTM) claims that the spreading of COVID-19 also very much depends on the lockdown decisions made by governments as well as COVID-19 protection measures carried out by citizens such as hand sanitisation and wearing masks. Eggo stated:A lot of places are unlocking, and a lot of places aren’t. We don’t really yet know what’s going to happen. Joseph Wu, a disease modeller from the University of Hong Kong also claims that ‘the future will very much depend on how much social mixing resumes, and what kind of prevention we do.’Dr Samir Bhatt, an infectious disease epidemiologist at Imperial College London also co-authored a study that observed that in 53 countries that are beginning to open up, there hasn’t been as surge as large as what was predicted in earlier data. Bhatt said:It’s undervalued how much people’s behaviour has changed in terms of masks, hand washing and social distancing. It’s nothing like it used to be.Looking at countries that are successfully squashing the virus such as China, New Zealand and Rwanda, it is clear that behavioural changes and early lockdowns can help slow transmission but only is everyone is on board. This evidence is compared with countries such as Brazil and the USA who opened their borders prematurely or never imposed them on a nationwide level and are now experiencing huge surges in infections.Researchers in virus hotspots have also been studying just how helpful personal coronavirus restriction measures. The study was conducted by researchers at the Anhembi Morumbi University in São Paulo, Brazil and consisted of over 250,000 mathematical models. The models observed social distancing measures in three levels described as constant, intermittent or ‘stepping-down’ with restrictions being reduced in stages with the addition of hand hygiene and mask-wearing. The study concluded that if 50-65% of people exercised caution in public then social distancing measures could be reduced every 80 days in order to prevent infection spikes over the space of just two years. However, this could be achieved even sooner once a safe vaccine is introduced.Getty ImagesWhat happens next?Seasons will also play a role in rates of infection over the course of the virus. It is clear that summer slowed the spread of the virus slightly but the effects weren’t consistent all over the world. However, with colder temperatures coming into play, rates of infection are already on the rise. Evidence suggests that the cold, dry air provides the ideal environment for the virus to spread. The cold weather will also drive people indoors where they are at an even bigger risk of infection through droplets. Richard Neher, a computational biologist at the University of Basel in Switzerland claims that that factors such as these will make the coronavirus harder to contain, especially in the northern hemisphere.However whether the virus will end in 2022, 2025 or even never will depend entirely on the introduction (and success) of a vaccine as well as human behaviour. So, make sure you maintain social distancing measures, wear your mask and wash your hands because your actions may have more impact than you think.