Many yogis have extraordinary experiences in terms of generating physical and mental energy through meditation. These experiences could be on a broad spectrum, ranging at one end, from a few hours or a few days of being turbo charged with energy and on the other end, as mentioned in our scriptures, to incredible feats of energy performed by saints and enlightened beings. For instance, the Gospel of Thomas verse 106 refers to energy that can move a mountain. The moment of the Buddha's Enlightenment is said to have rocked the universe. At a time when the entire planet is being 'rocked' by a virus, with no vaccine in the foreseeable future, would it be worth our while to collectively shift our focus to build a degree of resistance to the virus through extended hours of meditation whilst in lockdown at home and also to encourage others to do so?
There needs to be a stricter formal policy against magical-thinking types of questions; they tend to get voted down into oblivion, on a know-one-when-I-see-one basis, but that doesn't really explain to people why their questions were banned.
All the health-wealth-sex-love-fame-and-success questions seem to be designed to attract only crank answers; and would have only crank answers, if they weren't promptly closed. Questions about where-can-I-find-a-truly-enlightened-guru-who-can-fix-everything seem to fall into the same category (and seem to attract unfortunate answers from messianic claimants) as well as the questions about how-can-I-physically-levitate-and-read-minds.
Questions of this sort (and the answers they receive) seem to harm the credibility of a site designed for serious academic study of historical Buddhist thought. And more significantly have the potential to mislead vulnerable people. People who are inclined to earnestly ask questions like that on a site like this are obviously vulnerable. Ideally there'd be a bot that would automatically reply to mystical truth-seekers that the Buddhist Sangha doesn't and didn't exist for these purposes, citing scriptural justification from authentic suttas.
While somebody might believe that meditation "should" prevent COVID-19 infection, might feel that one karmically "deserves" to be uninfected, and might attempt to construe certain suttas to support that view... it remains that there is not one known case of meditation preventing COVID-19 infection. It would be irresponsible in the extreme to suggest that meditation can prevent COVID-19 infection.
...to build a degree of resistance to the virus through extended hours of meditation whilst in lockdown at home and also to encourage others to do so?
Actually scientific research on meditation does prove that it reduces stress level and the Cortisol stress hormone, hence giving a boost to one's own immune system. But with that said, during lockdown, one shouldn't just solely do sitting meditation. Don't forget to do some real physical exercises also. That'd make a win-win combo. Stay safe everyone!
Metta meditation in times like this might help if I am to speculate, as it generates much positive karma. But there is not definitive that the positive collective karma generated might specifically help with Coronavirus situation as karmic consequences are only truly understood by a Buddha. Nevertheless, if many people can do Metta meditation there will be some positive outcome.
Thought meditation is definitely a worth and good use of one's time spent in lockdown possibly also having a positive impact it is also absolutely necessary to take all needed medical precautions and not doing so would seriously out weight the positive benefits reaped from meditation.
It's funny that everyone is so upset by this virus. Did you know that atmospheric pollution kills 9 millions people each year, and harms the quality of life or billions of beings? Yet nobody lifted a finger. Not to mention that our beautiful planet, and all its ressources, was going down the drain at fast pace.
So to come back to the question, i will give a very personnal opinion. I don't think meditation only can prevent a virus infection. However, from a very long and personnal interest in the relationship between health, mind, emotions, energy, i would say that paying close attention to maintaining a positive mindset, healthy habits, avoiding sources of stress and bad karmas as much as possible will be hugely beneficial toward health and virus resistance.