There is nothing wrong with standing on one’s own behind the row for a reason, such as finding that the row is complete, as the obligatory parts of the prayer – in general – are waived when there is a valid excuse. If someone is afraid of catching some sickness or becoming infected with covid-19, so he prays on his own standing behind the row, his prayer is valid, because even though he omitted something obligatory, he omitted it for a valid reason.

If the worshippers are spaced out in the row because of precautionary measures required due to the pandemic, then there is no longer any reason to prevent praying between the pillars, and it is not disliked (makruh) to stand in a row between them in this case.

There is nothing wrong with having a test or swab for Covid-19 during the day in Ramadan, whether the swab is taken from the mouth or the nose, because insertion of the instrument into the throat or nose does not break the fast.

There is nothing wrong with receiving the Covid-19 vaccine during the day in Ramadan, because it comes under the heading of injections for medical purposes, which do not break the fast, because they are not food or drink, and do not come under the same heading as food and drink.

If cells taken from aborted foetuses are used in the vaccine, and we are unaware of the nature of these foetuses and whether they were miscarried naturally or aborted deliberately, for an Islamically legitimate reason or otherwise, then what appears to be the case is that it is permissible to receive this vaccine, because we are not certain as to whether its source is haraam, and the basic principle is that things are permissible. For more information, please see the long answer.